fix: implement ApSO

Signed-off-by: Dr. Carsten Leue <carsten.leue@de.ibm.com>

.github/workflows/build.yml

@@ -42,6 +42,7 @@ jobs:
           go test -v -race -coverprofile=coverage.txt -covermode=atomic ./...
       
       - name: Upload coverage to Coveralls
+        continue-on-error: true
         uses: coverallsapp/github-action@v2
         with:
           github-token: ${{ secrets.GITHUB_TOKEN }}
@@ -81,6 +82,7 @@ jobs:
           go test -v -race -coverprofile=coverage.txt -covermode=atomic ./...
       
       - name: Upload coverage to Coveralls
+        continue-on-error: true
         uses: coverallsapp/github-action@v2
         with:
           github-token: ${{ secrets.GITHUB_TOKEN }}
@@ -106,6 +108,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Coveralls Finished
+        continue-on-error: true
         uses: coverallsapp/github-action@v2
         with:
           github-token: ${{ secrets.GITHUB_TOKEN }}

v2/assert/from_test.go

@@ -29,7 +29,7 @@ func TestFromReaderIOResult(t *testing.T) {
 		ri := func(ctx context.Context) func() result.Result[Reader] {
 			return func() result.Result[Reader] {
 				// Return a Reader that always passes
-				return result.Of[Reader](func(t *testing.T) bool {
+				return result.Of(func(t *testing.T) bool {
 					return true
 				})
 			}
@@ -46,7 +46,7 @@ func TestFromReaderIOResult(t *testing.T) {
 		// Create a ReaderIOResult that returns a successful Equal assertion
 		ri := func(ctx context.Context) func() result.Result[Reader] {
 			return func() result.Result[Reader] {
-				return result.Of[Reader](Equal(42)(42))
+				return result.Of(Equal(42)(42))
 			}
 		}
 
@@ -80,7 +80,7 @@ func TestFromReaderIOResult(t *testing.T) {
 		// Create a ReaderIOResult that returns a failing assertion
 		ri := func(ctx context.Context) func() result.Result[Reader] {
 			return func() result.Result[Reader] {
-				return result.Of[Reader](Equal(42)(43))
+				return result.Of(Equal(42)(43))
 			}
 		}
 
@@ -100,7 +100,7 @@ func TestFromReaderIOResult(t *testing.T) {
 				contextUsed = true
 			}
 			return func() result.Result[Reader] {
-				return result.Of[Reader](func(t *testing.T) bool {
+				return result.Of(func(t *testing.T) bool {
 					return true
 				})
 			}
@@ -118,7 +118,7 @@ func TestFromReaderIOResult(t *testing.T) {
 		// Create a ReaderIOResult that returns NoError assertion
 		ri := func(ctx context.Context) func() result.Result[Reader] {
 			return func() result.Result[Reader] {
-				return result.Of[Reader](NoError(nil))
+				return result.Of(NoError(nil))
 			}
 		}
 
@@ -139,7 +139,7 @@ func TestFromReaderIOResult(t *testing.T) {
 					ArrayLength[int](3)(arr),
 					ArrayContains(2)(arr),
 				})
-				return result.Of[Reader](assertions)
+				return result.Of(assertions)
 			}
 		}
 
@@ -297,7 +297,7 @@ func TestFromReaderIO(t *testing.T) {
 		// Create a ReaderIO with Result assertions
 		ri := func(ctx context.Context) func() Reader {
 			return func() Reader {
-				successResult := result.Of[int](42)
+				successResult := result.Of(42)
 				return Success(successResult)
 			}
 		}
@@ -338,7 +338,7 @@ func TestFromReaderIOResultIntegration(t *testing.T) {
 				}
 
 				// Return a successful assertion
-				return result.Of[Reader](Equal("test")("test"))
+				return result.Of(Equal("test")("test"))
 			}
 		}
 

v2/cli/apply.go

@@ -21,7 +21,6 @@ import (
 	"log"
 	"os"
 	"path/filepath"
-	"time"
 
 	C "github.com/urfave/cli/v3"
 )
@@ -388,8 +387,8 @@ func generateApplyHelpers(filename string, count int) error {
 
 	// some header
 	fmt.Fprintln(f, "// Code generated by go generate; DO NOT EDIT.")
-	fmt.Fprintln(f, "// This file was generated by robots at")
-	fmt.Fprintf(f, "// %s\n\n", time.Now())
+	fmt.Fprintln(f, "// This file was generated by robots.")
+	fmt.Fprintln(f)
 
 	fmt.Fprintf(f, "package %s\n\n", pkg)
 

v2/cli/bind.go

@@ -21,7 +21,6 @@ import (
 	"log"
 	"os"
 	"path/filepath"
-	"time"
 
 	C "github.com/urfave/cli/v3"
 )
@@ -266,8 +265,8 @@ func generateBindHelpers(filename string, count int) error {
 
 	// some header
 	fmt.Fprintln(f, "// Code generated by go generate; DO NOT EDIT.")
-	fmt.Fprintln(f, "// This file was generated by robots at")
-	fmt.Fprintf(f, "// %s\n\n", time.Now())
+	fmt.Fprintln(f, "// This file was generated by robots.")
+	fmt.Fprintln(f)
 
 	fmt.Fprintf(f, "package %s\n", pkg)
 

v2/cli/di.go

@@ -21,7 +21,6 @@ import (
 	"log"
 	"os"
 	"path/filepath"
-	"time"
 
 	C "github.com/urfave/cli/v3"
 )
@@ -189,8 +188,8 @@ func generateDIHelpers(filename string, count int) error {
 
 	// some header
 	fmt.Fprintln(f, "// Code generated by go generate; DO NOT EDIT.")
-	fmt.Fprintln(f, "// This file was generated by robots at")
-	fmt.Fprintf(f, "// %s\n\n", time.Now())
+	fmt.Fprintln(f, "// This file was generated by robots.")
+	fmt.Fprintln(f)
 
 	fmt.Fprintf(f, "package %s\n\n", pkg)
 

v2/cli/either.go

@@ -21,7 +21,6 @@ import (
 	"log"
 	"os"
 	"path/filepath"
-	"time"
 
 	C "github.com/urfave/cli/v3"
 )
@@ -148,8 +147,8 @@ func generateEitherHelpers(filename string, count int) error {
 
 	// some header
 	fmt.Fprintln(f, "// Code generated by go generate; DO NOT EDIT.")
-	fmt.Fprintln(f, "// This file was generated by robots at")
-	fmt.Fprintf(f, "// %s\n\n", time.Now())
+	fmt.Fprintln(f, "// This file was generated by robots.")
+	fmt.Fprintln(f)
 
 	fmt.Fprintf(f, "package %s\n\n", pkg)
 

v2/cli/header.go

@@ -18,7 +18,6 @@ package cli
 import (
 	"fmt"
 	"os"
-	"time"
 )
 
 func writePackage(f *os.File, pkg string) {
@@ -26,6 +25,6 @@ func writePackage(f *os.File, pkg string) {
 	fmt.Fprintf(f, "package %s\n\n", pkg)
 	// some header
 	fmt.Fprintln(f, "// Code generated by go generate; DO NOT EDIT.")
-	fmt.Fprintln(f, "// This file was generated by robots at")
-	fmt.Fprintf(f, "// %s\n\n", time.Now())
+	fmt.Fprintln(f, "// This file was generated by robots.")
+	fmt.Fprintln(f)
 }

v2/cli/identity.go

@@ -21,7 +21,6 @@ import (
 	"log"
 	"os"
 	"path/filepath"
-	"time"
 
 	C "github.com/urfave/cli/v3"
 )
@@ -62,8 +61,8 @@ func generateIdentityHelpers(filename string, count int) error {
 
 	// some header
 	fmt.Fprintln(f, "// Code generated by go generate; DO NOT EDIT.")
-	fmt.Fprintln(f, "// This file was generated by robots at")
-	fmt.Fprintf(f, "// %s\n\n", time.Now())
+	fmt.Fprintln(f, "// This file was generated by robots.")
+	fmt.Fprintln(f)
 
 	fmt.Fprintf(f, "package %s\n\n", pkg)
 

v2/cli/io.go

@@ -21,7 +21,6 @@ import (
 	"log"
 	"os"
 	"path/filepath"
-	"time"
 
 	A "github.com/IBM/fp-go/v2/array"
 	C "github.com/urfave/cli/v3"
@@ -71,8 +70,8 @@ func generateIOHelpers(filename string, count int) error {
 
 	// some header
 	fmt.Fprintln(f, "// Code generated by go generate; DO NOT EDIT.")
-	fmt.Fprintln(f, "// This file was generated by robots at")
-	fmt.Fprintf(f, "// %s\n\n", time.Now())
+	fmt.Fprintln(f, "// This file was generated by robots.")
+	fmt.Fprintln(f)
 
 	fmt.Fprintf(f, "package %s\n\n", pkg)
 

v2/cli/ioeither.go

@@ -21,7 +21,6 @@ import (
 	"log"
 	"os"
 	"path/filepath"
-	"time"
 
 	A "github.com/IBM/fp-go/v2/array"
 	C "github.com/urfave/cli/v3"
@@ -219,8 +218,8 @@ func generateIOEitherHelpers(filename string, count int) error {
 
 	// some header
 	fmt.Fprintln(f, "// Code generated by go generate; DO NOT EDIT.")
-	fmt.Fprintln(f, "// This file was generated by robots at")
-	fmt.Fprintf(f, "// %s\n\n", time.Now())
+	fmt.Fprintln(f, "// This file was generated by robots.")
+	fmt.Fprintln(f)
 
 	fmt.Fprintf(f, "package %s\n\n", pkg)
 
@@ -234,8 +233,7 @@ import (
 
 	// some header
 	fmt.Fprintln(fg, "// Code generated by go generate; DO NOT EDIT.")
-	fmt.Fprintln(fg, "// This file was generated by robots at")
-	fmt.Fprintf(fg, "// %s\n", time.Now())
+	fmt.Fprintln(fg, "// This file was generated by robots.")
 
 	fmt.Fprintf(fg, "package generic\n\n")
 

v2/cli/iooption.go

@@ -21,7 +21,6 @@ import (
 	"log"
 	"os"
 	"path/filepath"
-	"time"
 
 	A "github.com/IBM/fp-go/v2/array"
 	C "github.com/urfave/cli/v3"
@@ -76,8 +75,8 @@ func generateIOOptionHelpers(filename string, count int) error {
 
 	// some header
 	fmt.Fprintln(f, "// Code generated by go generate; DO NOT EDIT.")
-	fmt.Fprintln(f, "// This file was generated by robots at")
-	fmt.Fprintf(f, "// %s\n\n", time.Now())
+	fmt.Fprintln(f, "// This file was generated by robots.")
+	fmt.Fprintln(f)
 
 	fmt.Fprintf(f, "package %s\n\n", pkg)
 

v2/cli/option.go

@@ -21,7 +21,6 @@ import (
 	"log"
 	"os"
 	"path/filepath"
-	"time"
 
 	C "github.com/urfave/cli/v3"
 )
@@ -148,8 +147,8 @@ func generateOptionHelpers(filename string, count int) error {
 
 	// some header
 	fmt.Fprintln(f, "// Code generated by go generate; DO NOT EDIT.")
-	fmt.Fprintln(f, "// This file was generated by robots at")
-	fmt.Fprintf(f, "// %s\n\n", time.Now())
+	fmt.Fprintln(f, "// This file was generated by robots.")
+	fmt.Fprintln(f)
 
 	fmt.Fprintf(f, "package %s\n\n", pkg)
 

v2/cli/pipe.go

@@ -21,7 +21,6 @@ import (
 	"log"
 	"os"
 	"path/filepath"
-	"time"
 
 	C "github.com/urfave/cli/v3"
 )
@@ -378,8 +377,8 @@ func generatePipeHelpers(filename string, count int) error {
 
 	// some header
 	fmt.Fprintln(f, "// Code generated by go generate; DO NOT EDIT.")
-	fmt.Fprintln(f, "// This file was generated by robots at")
-	fmt.Fprintf(f, "// %s\n\n", time.Now())
+	fmt.Fprintln(f, "// This file was generated by robots.")
+	fmt.Fprintln(f)
 
 	fmt.Fprintf(f, "package %s\n", pkg)
 

v2/cli/reader.go

@@ -21,7 +21,6 @@ import (
 	"log"
 	"os"
 	"path/filepath"
-	"time"
 
 	C "github.com/urfave/cli/v3"
 )
@@ -118,8 +117,8 @@ func generateReaderHelpers(filename string, count int) error {
 
 	// some header
 	fmt.Fprintln(f, "// Code generated by go generate; DO NOT EDIT.")
-	fmt.Fprintln(f, "// This file was generated by robots at")
-	fmt.Fprintf(f, "// %s\n\n", time.Now())
+	fmt.Fprintln(f, "// This file was generated by robots.")
+	fmt.Fprintln(f)
 
 	fmt.Fprintf(f, "package %s\n\n", pkg)
 
@@ -131,8 +130,7 @@ import (
 
 	// some header
 	fmt.Fprintln(fg, "// Code generated by go generate; DO NOT EDIT.")
-	fmt.Fprintln(fg, "// This file was generated by robots at")
-	fmt.Fprintf(fg, "// %s\n", time.Now())
+	fmt.Fprintln(fg, "// This file was generated by robots.")
 
 	fmt.Fprintf(fg, "package generic\n\n")
 

v2/cli/readerioeither.go

@@ -21,7 +21,6 @@ import (
 	"log"
 	"os"
 	"path/filepath"
-	"time"
 
 	C "github.com/urfave/cli/v3"
 )
@@ -233,8 +232,8 @@ func generateReaderIOEitherHelpers(filename string, count int) error {
 
 	// some header
 	fmt.Fprintln(f, "// Code generated by go generate; DO NOT EDIT.")
-	fmt.Fprintln(f, "// This file was generated by robots at")
-	fmt.Fprintf(f, "// %s\n\n", time.Now())
+	fmt.Fprintln(f, "// This file was generated by robots.")
+	fmt.Fprintln(f)
 
 	fmt.Fprintf(f, "package %s\n\n", pkg)
 
@@ -246,8 +245,7 @@ import (
 
 	// some header
 	fmt.Fprintln(fg, "// Code generated by go generate; DO NOT EDIT.")
-	fmt.Fprintln(fg, "// This file was generated by robots at")
-	fmt.Fprintf(fg, "// %s\n", time.Now())
+	fmt.Fprintln(fg, "// This file was generated by robots.")
 
 	fmt.Fprintf(fg, "package generic\n\n")
 

v2/cli/tuple.go

@@ -22,7 +22,6 @@ import (
 	"os"
 	"path/filepath"
 	"strings"
-	"time"
 
 	C "github.com/urfave/cli/v3"
 )
@@ -399,8 +398,8 @@ func generateTupleHelpers(filename string, count int) error {
 
 	// some header
 	fmt.Fprintln(f, "// Code generated by go generate; DO NOT EDIT.")
-	fmt.Fprintln(f, "// This file was generated by robots at")
-	fmt.Fprintf(f, "// %s\n\n", time.Now())
+	fmt.Fprintln(f, "// This file was generated by robots.")
+	fmt.Fprintln(f)
 
 	fmt.Fprintf(f, "package %s\n\n", pkg)
 

v2/constant/const.go

@@ -13,6 +13,37 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+// Package constant provides the Const functor, a phantom type that ignores its second type parameter.
+//
+// The Const functor is a fundamental building block in functional programming that wraps a value
+// of type E while having a phantom type parameter A. This makes it useful for:
+//   - Accumulating values during traversals (e.g., collecting metadata)
+//   - Implementing optics (lenses, prisms) where you need to track information
+//   - Building applicative functors that combine values using a semigroup
+//
+// # The Const Functor
+//
+// Const[E, A] wraps a value of type E and has a phantom type parameter A that doesn't affect
+// the runtime value. This allows it to participate in functor and applicative operations while
+// maintaining the wrapped value unchanged.
+//
+// # Key Properties
+//
+//   - Map operations ignore the function and preserve the wrapped value
+//   - Ap operations combine wrapped values using a semigroup
+//   - The phantom type A allows type-safe composition with other functors
+//
+// # Example Usage
+//
+//	// Accumulate string values
+//	c1 := Make[string, int]("hello")
+//	c2 := Make[string, int]("world")
+//
+//	// Map doesn't change the wrapped value
+//	mapped := Map[string, int, string](strconv.Itoa)(c1)  // Still contains "hello"
+//
+//	// Ap combines values using a semigroup
+//	combined := Ap[string, int, int](S.Monoid)(c1)(c2)  // Contains "helloworld"
 package constant
 
 import (
@@ -21,36 +52,209 @@ import (
 	S "github.com/IBM/fp-go/v2/semigroup"
 )
 
+// Const is a functor that wraps a value of type E with a phantom type parameter A.
+//
+// The Const functor is useful for accumulating values during traversals or implementing
+// optics. The type parameter A is phantom - it doesn't affect the runtime value but allows
+// the type to participate in functor and applicative operations.
+//
+// Type Parameters:
+//   - E: The type of the wrapped value (the actual data)
+//   - A: The phantom type parameter (not stored, only used for type-level operations)
+//
+// Example:
+//
+//	// Create a Const that wraps a string
+//	c := Make[string, int]("metadata")
+//
+//	// The int type parameter is phantom - no int value is stored
+//	value := Unwrap(c)  // "metadata"
 type Const[E, A any] struct {
 	value E
 }
 
+// Make creates a Const value wrapping the given value.
+//
+// This is the primary constructor for Const values. The second type parameter A
+// is phantom and must be specified explicitly when needed for type inference.
+//
+// Type Parameters:
+//   - E: The type of the value to wrap
+//   - A: The phantom type parameter
+//
+// Parameters:
+//   - e: The value to wrap
+//
+// Returns:
+//   - A Const[E, A] wrapping the value
+//
+// Example:
+//
+//	c := Make[string, int]("hello")
+//	value := Unwrap(c)  // "hello"
 func Make[E, A any](e E) Const[E, A] {
 	return Const[E, A]{value: e}
 }
 
+// Unwrap extracts the wrapped value from a Const.
+//
+// This is the inverse of Make, retrieving the actual value stored in the Const.
+//
+// Type Parameters:
+//   - E: The type of the wrapped value
+//   - A: The phantom type parameter
+//
+// Parameters:
+//   - c: The Const to unwrap
+//
+// Returns:
+//   - The wrapped value of type E
+//
+// Example:
+//
+//	c := Make[string, int]("world")
+//	value := Unwrap(c)  // "world"
 func Unwrap[E, A any](c Const[E, A]) E {
 	return c.value
 }
 
+// Of creates a Const containing the monoid's empty value, ignoring the input.
+//
+// This implements the Applicative's "pure" operation for Const. It creates a Const
+// wrapping the monoid's identity element, regardless of the input value.
+//
+// Type Parameters:
+//   - E: The type of the wrapped value (must have a monoid)
+//   - A: The input type (ignored)
+//
+// Parameters:
+//   - m: The monoid providing the empty value
+//
+// Returns:
+//   - A function that ignores its input and returns Const[E, A] with the empty value
+//
+// Example:
+//
+//	import S "github.com/IBM/fp-go/v2/string"
+//
+//	of := Of[string, int](S.Monoid)
+//	c := of(42)  // Const[string, int] containing ""
+//	value := Unwrap(c)  // ""
 func Of[E, A any](m M.Monoid[E]) func(A) Const[E, A] {
 	return F.Constant1[A](Make[E, A](m.Empty()))
 }
 
+// MonadMap applies a function to the phantom type parameter without changing the wrapped value.
+//
+// This implements the Functor's map operation for Const. Since the type parameter A is phantom,
+// the function is never actually called - the wrapped value E remains unchanged.
+//
+// Type Parameters:
+//   - E: The type of the wrapped value
+//   - A: The input phantom type
+//   - B: The output phantom type
+//
+// Parameters:
+//   - fa: The Const to map over
+//   - _: The function to apply (ignored)
+//
+// Returns:
+//   - A Const[E, B] with the same wrapped value
+//
+// Example:
+//
+//	c := Make[string, int]("hello")
+//	mapped := MonadMap(c, func(i int) string { return strconv.Itoa(i) })
+//	// mapped still contains "hello", function was never called
 func MonadMap[E, A, B any](fa Const[E, A], _ func(A) B) Const[E, B] {
 	return Make[E, B](fa.value)
 }
 
+// MonadAp combines two Const values using a semigroup.
+//
+// This implements the Applicative's ap operation for Const. It combines the wrapped
+// values from both Const instances using the provided semigroup, ignoring the function
+// type in the first argument.
+//
+// Type Parameters:
+//   - E: The type of the wrapped values (must have a semigroup)
+//   - A: The input phantom type
+//   - B: The output phantom type
+//
+// Parameters:
+//   - s: The semigroup for combining wrapped values
+//
+// Returns:
+//   - A function that takes two Const values and combines their wrapped values
+//
+// Example:
+//
+//	import S "github.com/IBM/fp-go/v2/string"
+//
+//	ap := MonadAp[string, int, int](S.Monoid)
+//	c1 := Make[string, func(int) int]("hello")
+//	c2 := Make[string, int]("world")
+//	result := ap(c1, c2)  // Const containing "helloworld"
 func MonadAp[E, A, B any](s S.Semigroup[E]) func(fab Const[E, func(A) B], fa Const[E, A]) Const[E, B] {
 	return func(fab Const[E, func(A) B], fa Const[E, A]) Const[E, B] {
 		return Make[E, B](s.Concat(fab.value, fa.value))
 	}
 }
 
+// Map applies a function to the phantom type parameter without changing the wrapped value.
+//
+// This is the curried version of MonadMap, providing a more functional programming style.
+// The function is never actually called since A is a phantom type.
+//
+// Type Parameters:
+//   - E: The type of the wrapped value
+//   - A: The input phantom type
+//   - B: The output phantom type
+//
+// Parameters:
+//   - f: The function to apply (ignored)
+//
+// Returns:
+//   - A function that transforms Const[E, A] to Const[E, B]
+//
+// Example:
+//
+//	import F "github.com/IBM/fp-go/v2/function"
+//
+//	c := Make[string, int]("data")
+//	mapped := F.Pipe1(c, Map[string, int, string](strconv.Itoa))
+//	// mapped still contains "data"
 func Map[E, A, B any](f func(A) B) func(fa Const[E, A]) Const[E, B] {
 	return F.Bind2nd(MonadMap[E, A, B], f)
 }
 
+// Ap combines Const values using a semigroup in a curried style.
+//
+// This is the curried version of MonadAp, providing data-last style for better composition.
+// It combines the wrapped values from both Const instances using the provided semigroup.
+//
+// Type Parameters:
+//   - E: The type of the wrapped values (must have a semigroup)
+//   - A: The input phantom type
+//   - B: The output phantom type
+//
+// Parameters:
+//   - s: The semigroup for combining wrapped values
+//
+// Returns:
+//   - A curried function for combining Const values
+//
+// Example:
+//
+//	import (
+//	    F "github.com/IBM/fp-go/v2/function"
+//	    S "github.com/IBM/fp-go/v2/string"
+//	)
+//
+//	c1 := Make[string, int]("hello")
+//	c2 := Make[string, func(int) int]("world")
+//	result := F.Pipe1(c1, Ap[string, int, int](S.Monoid)(c2))
+//	// result contains "helloworld"
 func Ap[E, A, B any](s S.Semigroup[E]) func(fa Const[E, A]) func(fab Const[E, func(A) B]) Const[E, B] {
 	monadap := MonadAp[E, A, B](s)
 	return func(fa Const[E, A]) func(fab Const[E, func(A) B]) Const[E, B] {

v2/constant/const_test.go

@@ -16,25 +16,340 @@
 package constant
 
 import (
+	"strconv"
 	"testing"
 
 	F "github.com/IBM/fp-go/v2/function"
 	"github.com/IBM/fp-go/v2/internal/utils"
+	N "github.com/IBM/fp-go/v2/number"
 	S "github.com/IBM/fp-go/v2/string"
 
 	"github.com/stretchr/testify/assert"
 )
 
-func TestMap(t *testing.T) {
-	fa := Make[string, int]("foo")
-	assert.Equal(t, fa, F.Pipe1(fa, Map[string](utils.Double)))
+// TestMake tests the Make constructor
+func TestMake(t *testing.T) {
+	t.Run("creates Const with string value", func(t *testing.T) {
+		c := Make[string, int]("hello")
+		assert.Equal(t, "hello", Unwrap(c))
+	})
+
+	t.Run("creates Const with int value", func(t *testing.T) {
+		c := Make[int, string](42)
+		assert.Equal(t, 42, Unwrap(c))
+	})
+
+	t.Run("creates Const with struct value", func(t *testing.T) {
+		type Config struct {
+			Name string
+			Port int
+		}
+		cfg := Config{Name: "server", Port: 8080}
+		c := Make[Config, bool](cfg)
+		assert.Equal(t, cfg, Unwrap(c))
+	})
 }
 
+// TestUnwrap tests extracting values from Const
+func TestUnwrap(t *testing.T) {
+	t.Run("unwraps string value", func(t *testing.T) {
+		c := Make[string, int]("world")
+		value := Unwrap(c)
+		assert.Equal(t, "world", value)
+	})
+
+	t.Run("unwraps empty string", func(t *testing.T) {
+		c := Make[string, int]("")
+		value := Unwrap(c)
+		assert.Equal(t, "", value)
+	})
+
+	t.Run("unwraps zero value", func(t *testing.T) {
+		c := Make[int, string](0)
+		value := Unwrap(c)
+		assert.Equal(t, 0, value)
+	})
+}
+
+// TestOf tests the Of function
 func TestOf(t *testing.T) {
-	assert.Equal(t, Make[string, int](""), Of[string, int](S.Monoid)(1))
+	t.Run("creates Const with monoid empty value", func(t *testing.T) {
+		of := Of[string, int](S.Monoid)
+		c := of(42)
+		assert.Equal(t, "", Unwrap(c))
+	})
+
+	t.Run("ignores input value", func(t *testing.T) {
+		of := Of[string, int](S.Monoid)
+		c1 := of(1)
+		c2 := of(100)
+		assert.Equal(t, Unwrap(c1), Unwrap(c2))
+	})
+
+	t.Run("works with int monoid", func(t *testing.T) {
+		of := Of[int, string](N.MonoidSum[int]())
+		c := of("ignored")
+		assert.Equal(t, 0, Unwrap(c))
+	})
 }
 
-func TestAp(t *testing.T) {
-	fab := Make[string, int]("bar")
-	assert.Equal(t, Make[string, int]("foobar"), Ap[string, int, int](S.Monoid)(fab)(Make[string, func(int) int]("foo")))
+// TestMap tests the Map function
+func TestMap(t *testing.T) {
+	t.Run("preserves wrapped value", func(t *testing.T) {
+		fa := Make[string, int]("foo")
+		result := F.Pipe1(fa, Map[string](utils.Double))
+		assert.Equal(t, "foo", Unwrap(result))
+	})
+
+	t.Run("changes phantom type", func(t *testing.T) {
+		fa := Make[string, int]("data")
+		fb := Map[string, int, string](strconv.Itoa)(fa)
+		// Value unchanged, but type changed from Const[string, int] to Const[string, string]
+		assert.Equal(t, "data", Unwrap(fb))
+	})
+
+	t.Run("function is never called", func(t *testing.T) {
+		called := false
+		fa := Make[string, int]("test")
+		fb := Map[string, int, string](func(i int) string {
+			called = true
+			return strconv.Itoa(i)
+		})(fa)
+		assert.False(t, called, "Map function should not be called")
+		assert.Equal(t, "test", Unwrap(fb))
+	})
+}
+
+// TestMonadMap tests the MonadMap function
+func TestMonadMap(t *testing.T) {
+	t.Run("preserves wrapped value", func(t *testing.T) {
+		fa := Make[string, int]("original")
+		fb := MonadMap(fa, func(i int) string { return strconv.Itoa(i) })
+		assert.Equal(t, "original", Unwrap(fb))
+	})
+
+	t.Run("works with different types", func(t *testing.T) {
+		fa := Make[int, string](42)
+		fb := MonadMap(fa, func(s string) bool { return len(s) > 0 })
+		assert.Equal(t, 42, Unwrap(fb))
+	})
+}
+
+// TestAp tests the Ap function
+func TestAp(t *testing.T) {
+	t.Run("combines string values", func(t *testing.T) {
+		fab := Make[string, int]("bar")
+		fa := Make[string, func(int) int]("foo")
+		result := Ap[string, int, int](S.Monoid)(fab)(fa)
+		assert.Equal(t, "foobar", Unwrap(result))
+	})
+
+	t.Run("combines int values with sum", func(t *testing.T) {
+		fab := Make[int, string](10)
+		fa := Make[int, func(string) string](5)
+		result := Ap[int, string, string](N.SemigroupSum[int]())(fab)(fa)
+		assert.Equal(t, 15, Unwrap(result))
+	})
+
+	t.Run("combines int values with product", func(t *testing.T) {
+		fab := Make[int, bool](3)
+		fa := Make[int, func(bool) bool](4)
+		result := Ap[int, bool, bool](N.SemigroupProduct[int]())(fab)(fa)
+		assert.Equal(t, 12, Unwrap(result))
+	})
+}
+
+// TestMonadAp tests the MonadAp function
+func TestMonadAp(t *testing.T) {
+	t.Run("combines values using semigroup", func(t *testing.T) {
+		ap := MonadAp[string, int, int](S.Monoid)
+		fab := Make[string, func(int) int]("hello")
+		fa := Make[string, int]("world")
+		result := ap(fab, fa)
+		assert.Equal(t, "helloworld", Unwrap(result))
+	})
+
+	t.Run("works with empty strings", func(t *testing.T) {
+		ap := MonadAp[string, int, int](S.Monoid)
+		fab := Make[string, func(int) int]("")
+		fa := Make[string, int]("test")
+		result := ap(fab, fa)
+		assert.Equal(t, "test", Unwrap(result))
+	})
+}
+
+// TestMonoid tests the Monoid function
+func TestMonoid(t *testing.T) {
+	t.Run("always returns constant value", func(t *testing.T) {
+		m := Monoid(42)
+		assert.Equal(t, 42, m.Concat(1, 2))
+		assert.Equal(t, 42, m.Concat(100, 200))
+		assert.Equal(t, 42, m.Empty())
+	})
+
+	t.Run("works with strings", func(t *testing.T) {
+		m := Monoid("constant")
+		assert.Equal(t, "constant", m.Concat("a", "b"))
+		assert.Equal(t, "constant", m.Empty())
+	})
+
+	t.Run("works with structs", func(t *testing.T) {
+		type Point struct{ X, Y int }
+		p := Point{X: 1, Y: 2}
+		m := Monoid(p)
+		assert.Equal(t, p, m.Concat(Point{X: 3, Y: 4}, Point{X: 5, Y: 6}))
+		assert.Equal(t, p, m.Empty())
+	})
+
+	t.Run("satisfies monoid laws", func(t *testing.T) {
+		m := Monoid(10)
+
+		// Left identity: Concat(Empty(), x) = x (both return constant)
+		assert.Equal(t, 10, m.Concat(m.Empty(), 5))
+
+		// Right identity: Concat(x, Empty()) = x (both return constant)
+		assert.Equal(t, 10, m.Concat(5, m.Empty()))
+
+		// Associativity: Concat(Concat(x, y), z) = Concat(x, Concat(y, z))
+		left := m.Concat(m.Concat(1, 2), 3)
+		right := m.Concat(1, m.Concat(2, 3))
+		assert.Equal(t, left, right)
+		assert.Equal(t, 10, left)
+	})
+}
+
+// TestConstFunctorLaws tests functor laws for Const
+func TestConstFunctorLaws(t *testing.T) {
+	t.Run("identity law", func(t *testing.T) {
+		// map id = id
+		fa := Make[string, int]("test")
+		mapped := Map[string, int, int](F.Identity[int])(fa)
+		assert.Equal(t, Unwrap(fa), Unwrap(mapped))
+	})
+
+	t.Run("composition law", func(t *testing.T) {
+		// map (g . f) = map g . map f
+		fa := Make[string, int]("data")
+		f := func(i int) string { return strconv.Itoa(i) }
+		g := func(s string) bool { return len(s) > 0 }
+
+		// map (g . f)
+		composed := Map[string, int, bool](func(i int) bool { return g(f(i)) })(fa)
+
+		// map g . map f
+		intermediate := F.Pipe1(fa, Map[string, int, string](f))
+		chained := Map[string, string, bool](g)(intermediate)
+
+		assert.Equal(t, Unwrap(composed), Unwrap(chained))
+	})
+}
+
+// TestConstApplicativeLaws tests applicative laws for Const
+func TestConstApplicativeLaws(t *testing.T) {
+	t.Run("identity law", func(t *testing.T) {
+		// For Const, ap combines the wrapped values using the semigroup
+		// ap (of id) v combines empty (from of) with v's value
+		v := Make[string, int]("value")
+		ofId := Of[string, func(int) int](S.Monoid)(F.Identity[int])
+		result := Ap[string, int, int](S.Monoid)(v)(ofId)
+		// Result combines "" (from Of) with "value" using string monoid
+		assert.Equal(t, "value", Unwrap(result))
+	})
+
+	t.Run("homomorphism law", func(t *testing.T) {
+		// ap (of f) (of x) = of (f x)
+		f := func(i int) string { return strconv.Itoa(i) }
+		x := 42
+
+		ofF := Of[string, func(int) string](S.Monoid)(f)
+		ofX := Of[string, int](S.Monoid)(x)
+		left := Ap[string, int, string](S.Monoid)(ofX)(ofF)
+
+		right := Of[string, string](S.Monoid)(f(x))
+
+		assert.Equal(t, Unwrap(left), Unwrap(right))
+	})
+}
+
+// TestConstEdgeCases tests edge cases
+func TestConstEdgeCases(t *testing.T) {
+	t.Run("empty string values", func(t *testing.T) {
+		c := Make[string, int]("")
+		assert.Equal(t, "", Unwrap(c))
+
+		mapped := Map[string, int, string](strconv.Itoa)(c)
+		assert.Equal(t, "", Unwrap(mapped))
+	})
+
+	t.Run("zero values", func(t *testing.T) {
+		c := Make[int, string](0)
+		assert.Equal(t, 0, Unwrap(c))
+	})
+
+	t.Run("nil pointer", func(t *testing.T) {
+		var ptr *int
+		c := Make[*int, string](ptr)
+		assert.Nil(t, Unwrap(c))
+	})
+
+	t.Run("multiple map operations", func(t *testing.T) {
+		c := Make[string, int]("original")
+		// Chain multiple map operations
+		step1 := Map[string, int, string](strconv.Itoa)(c)
+		step2 := Map[string, string, bool](func(s string) bool { return len(s) > 0 })(step1)
+		result := Map[string, bool, int](func(b bool) int {
+			if b {
+				return 1
+			}
+			return 0
+		})(step2)
+		assert.Equal(t, "original", Unwrap(result))
+	})
+}
+
+// BenchmarkMake benchmarks the Make constructor
+func BenchmarkMake(b *testing.B) {
+	b.ResetTimer()
+	for b.Loop() {
+		_ = Make[string, int]("test")
+	}
+}
+
+// BenchmarkUnwrap benchmarks the Unwrap function
+func BenchmarkUnwrap(b *testing.B) {
+	c := Make[string, int]("test")
+	b.ResetTimer()
+	for b.Loop() {
+		_ = Unwrap(c)
+	}
+}
+
+// BenchmarkMap benchmarks the Map function
+func BenchmarkMap(b *testing.B) {
+	c := Make[string, int]("test")
+	mapFn := Map[string, int, string](strconv.Itoa)
+	b.ResetTimer()
+	for b.Loop() {
+		_ = mapFn(c)
+	}
+}
+
+// BenchmarkAp benchmarks the Ap function
+func BenchmarkAp(b *testing.B) {
+	fab := Make[string, int]("hello")
+	fa := Make[string, func(int) int]("world")
+	apFn := Ap[string, int, int](S.Monoid)
+	b.ResetTimer()
+	for b.Loop() {
+		_ = apFn(fab)(fa)
+	}
+}
+
+// BenchmarkMonoid benchmarks the Monoid function
+func BenchmarkMonoid(b *testing.B) {
+	m := Monoid(42)
+	b.ResetTimer()
+	for b.Loop() {
+		_ = m.Concat(1, 2)
+	}
 }

v2/constant/monoid.go

@@ -1,3 +1,18 @@
+// Copyright (c) 2023 - 2025 IBM Corp.
+// All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
 package constant
 
 import (
@@ -5,7 +20,47 @@ import (
 	M "github.com/IBM/fp-go/v2/monoid"
 )
 
-// Monoid returns a [M.Monoid] that returns a constant value in all operations
+// Monoid creates a monoid that always returns a constant value.
+//
+// This creates a trivial monoid where both the Concat operation and Empty
+// always return the same constant value, regardless of inputs. This is useful
+// for testing, placeholder implementations, or when you need a monoid instance
+// but the actual combining behavior doesn't matter.
+//
+// # Monoid Laws
+//
+// The constant monoid satisfies all monoid laws trivially:
+//   - Associativity: Concat(Concat(x, y), z) = Concat(x, Concat(y, z)) - always returns 'a'
+//   - Left Identity: Concat(Empty(), x) = x - both return 'a'
+//   - Right Identity: Concat(x, Empty()) = x - both return 'a'
+//
+// Type Parameters:
+//   - A: The type of the constant value
+//
+// Parameters:
+//   - a: The constant value to return in all operations
+//
+// Returns:
+//   - A Monoid[A] that always returns the constant value
+//
+// Example:
+//
+//	// Create a monoid that always returns 42
+//	m := Monoid(42)
+//	result := m.Concat(1, 2)  // 42
+//	empty := m.Empty()         // 42
+//
+//	// Useful for testing or placeholder implementations
+//	type Config struct {
+//	    Timeout int
+//	}
+//	defaultConfig := Monoid(Config{Timeout: 30})
+//	config := defaultConfig.Concat(Config{Timeout: 10}, Config{Timeout: 20})
+//	// config is Config{Timeout: 30}
+//
+// See also:
+//   - function.Constant2: The underlying constant function
+//   - M.MakeMonoid: The monoid constructor
 func Monoid[A any](a A) M.Monoid[A] {
 	return M.MakeMonoid(function.Constant2[A, A](a), a)
 }

v2/context/readerioresult/file/file.go

@@ -83,6 +83,45 @@ var (
 		RIOE.WithContext[*os.File],
 	)
 
+	// Create creates or truncates a file for writing within the given context.
+	// If the file already exists, it is truncated. If it doesn't exist, it is created
+	// with mode 0666 (before umask).
+	//
+	// The operation respects context cancellation and returns a ReaderIOResult
+	// that produces an os.File handle on success.
+	//
+	// The returned file handle should be closed using the Close function when no longer needed,
+	// or managed automatically using WithResource or WriteFile.
+	//
+	// Parameters:
+	//   - path: The path to the file to create or truncate
+	//
+	// Returns:
+	//   - ReaderIOResult[*os.File]: A context-aware computation that creates the file
+	//
+	// Example:
+	//
+	//	createFile := Create("output.txt")
+	//	result := createFile(ctx)()
+	//	either.Fold(
+	//	    result,
+	//	    func(err error) { log.Printf("Error: %v", err) },
+	//	    func(f *os.File) {
+	//	        defer f.Close()
+	//	        f.WriteString("Hello, World!")
+	//	    },
+	//	)
+	//
+	// See Also:
+	//   - WriteFile: For writing data to a file with automatic resource management
+	//   - Open: For opening files for reading
+	//   - Close: For closing file handles
+	Create = F.Flow3(
+		IOEF.Create,
+		RIOE.FromIOEither[*os.File],
+		RIOE.WithContext[*os.File],
+	)
+
 	// Remove removes a file by name.
 	// The operation returns the filename on success, allowing for easy composition
 	// with other file operations.
@@ -191,3 +230,48 @@ func ReadFile(path string) ReaderIOResult[[]byte] {
 		}
 	})
 }
+
+// WriteFile writes data to a file in a context-aware manner.
+// This function automatically manages the file resource using the RAII pattern,
+// ensuring the file is properly closed even if an error occurs or the context is canceled.
+//
+// If the file doesn't exist, it is created with mode 0666 (before umask).
+// If the file already exists, it is truncated before writing.
+//
+// The operation:
+//   - Creates or truncates the file for writing
+//   - Writes all data to the file
+//   - Automatically closes the file when done
+//   - Respects context cancellation during the write operation
+//
+// Parameters:
+//   - data: The byte slice to write to the file
+//
+// Returns:
+//   - Kleisli[string, []byte]: A function that takes a file path and returns a computation
+//     that writes the data and returns the written bytes on success
+//
+// Example:
+//
+//	writeOp := WriteFile([]byte("Hello, World!"))
+//	result := writeOp("output.txt")(ctx)()
+//	either.Fold(
+//	    result,
+//	    func(err error) { log.Printf("Write error: %v", err) },
+//	    func(data []byte) { log.Printf("Wrote %d bytes", len(data)) },
+//	)
+//
+// The function uses WithResource internally to ensure proper cleanup:
+//
+//	WriteFile(data) = Create >> WriteAll(data) >> Close
+//
+// See Also:
+//   - ReadFile: For reading file contents with automatic resource management
+//   - Create: For creating files without automatic writing
+//   - WriteAll: For writing to an already-open file handle
+func WriteFile(data []byte) Kleisli[string, []byte] {
+	return F.Flow2(
+		Create,
+		WriteAll[*os.File](data),
+	)
+}

v2/context/readerioresult/file/file_test.go

@@ -18,11 +18,16 @@ package file
 import (
 	"context"
 	"fmt"
+	"os"
+	"path/filepath"
+	"testing"
 
 	R "github.com/IBM/fp-go/v2/context/readerioresult"
+	E "github.com/IBM/fp-go/v2/either"
 	F "github.com/IBM/fp-go/v2/function"
 	"github.com/IBM/fp-go/v2/io"
 	J "github.com/IBM/fp-go/v2/json"
+	"github.com/stretchr/testify/assert"
 )
 
 type RecordType struct {
@@ -49,3 +54,267 @@ func ExampleReadFile() {
 	// Output:
 	// Right[string](Carsten)
 }
+
+func TestCreate(t *testing.T) {
+	ctx := context.Background()
+
+	t.Run("Success - creates new file", func(t *testing.T) {
+		tempFile := filepath.Join(t.TempDir(), "test_create.txt")
+
+		createOp := Create(tempFile)
+		result := createOp(ctx)()
+
+		assert.True(t, E.IsRight(result))
+
+		// Verify file was created
+		_, err := os.Stat(tempFile)
+		assert.NoError(t, err)
+
+		// Clean up file handle
+		E.MonadFold(result,
+			func(error) *os.File { return nil },
+			func(f *os.File) *os.File { f.Close(); return f },
+		)
+	})
+
+	t.Run("Success - truncates existing file", func(t *testing.T) {
+		tempFile := filepath.Join(t.TempDir(), "test_truncate.txt")
+
+		// Create file with initial content
+		err := os.WriteFile(tempFile, []byte("initial content"), 0644)
+		assert.NoError(t, err)
+
+		// Create should truncate
+		createOp := Create(tempFile)
+		result := createOp(ctx)()
+
+		assert.True(t, E.IsRight(result))
+
+		// Close the file
+		E.MonadFold(result,
+			func(error) *os.File { return nil },
+			func(f *os.File) *os.File { f.Close(); return f },
+		)
+
+		// Verify file was truncated
+		content, err := os.ReadFile(tempFile)
+		assert.NoError(t, err)
+		assert.Empty(t, content)
+	})
+
+	t.Run("Failure - invalid path", func(t *testing.T) {
+		// Try to create file in non-existent directory
+		invalidPath := filepath.Join(t.TempDir(), "nonexistent", "test.txt")
+
+		createOp := Create(invalidPath)
+		result := createOp(ctx)()
+
+		assert.True(t, E.IsLeft(result))
+	})
+
+	t.Run("Success - file can be written to", func(t *testing.T) {
+		tempFile := filepath.Join(t.TempDir(), "test_write.txt")
+
+		createOp := Create(tempFile)
+		result := createOp(ctx)()
+
+		assert.True(t, E.IsRight(result))
+
+		// Write to the file
+		E.MonadFold(result,
+			func(err error) *os.File { t.Fatalf("Unexpected error: %v", err); return nil },
+			func(f *os.File) *os.File {
+				defer f.Close()
+				_, err := f.WriteString("test content")
+				assert.NoError(t, err)
+				return f
+			},
+		)
+
+		// Verify content was written
+		content, err := os.ReadFile(tempFile)
+		assert.NoError(t, err)
+		assert.Equal(t, "test content", string(content))
+	})
+
+	t.Run("Context cancellation", func(t *testing.T) {
+		cancelCtx, cancel := context.WithCancel(context.Background())
+		cancel() // Cancel immediately
+
+		tempFile := filepath.Join(t.TempDir(), "test_cancel.txt")
+
+		createOp := Create(tempFile)
+		result := createOp(cancelCtx)()
+
+		// Note: File creation itself doesn't check context, but this tests the pattern
+		// In practice, context cancellation would affect subsequent operations
+		_ = result
+	})
+}
+
+func TestWriteFile(t *testing.T) {
+	ctx := context.Background()
+
+	t.Run("Success - writes data to new file", func(t *testing.T) {
+		tempFile := filepath.Join(t.TempDir(), "test_write.txt")
+		testData := []byte("Hello, World!")
+
+		writeOp := WriteFile(testData)
+		result := writeOp(tempFile)(ctx)()
+
+		assert.True(t, E.IsRight(result))
+
+		// Verify returned data
+		E.MonadFold(result,
+			func(err error) []byte { t.Fatalf("Unexpected error: %v", err); return nil },
+			func(data []byte) []byte {
+				assert.Equal(t, testData, data)
+				return data
+			},
+		)
+
+		// Verify file content
+		content, err := os.ReadFile(tempFile)
+		assert.NoError(t, err)
+		assert.Equal(t, testData, content)
+	})
+
+	t.Run("Success - overwrites existing file", func(t *testing.T) {
+		tempFile := filepath.Join(t.TempDir(), "test_overwrite.txt")
+
+		// Write initial content
+		err := os.WriteFile(tempFile, []byte("old content"), 0644)
+		assert.NoError(t, err)
+
+		// Overwrite with new content
+		newData := []byte("new content")
+		writeOp := WriteFile(newData)
+		result := writeOp(tempFile)(ctx)()
+
+		assert.True(t, E.IsRight(result))
+
+		// Verify file was overwritten
+		content, err := os.ReadFile(tempFile)
+		assert.NoError(t, err)
+		assert.Equal(t, newData, content)
+	})
+
+	t.Run("Success - writes empty data", func(t *testing.T) {
+		tempFile := filepath.Join(t.TempDir(), "test_empty.txt")
+		emptyData := []byte{}
+
+		writeOp := WriteFile(emptyData)
+		result := writeOp(tempFile)(ctx)()
+
+		assert.True(t, E.IsRight(result))
+
+		// Verify file is empty
+		content, err := os.ReadFile(tempFile)
+		assert.NoError(t, err)
+		assert.Empty(t, content)
+	})
+
+	t.Run("Success - writes large data", func(t *testing.T) {
+		tempFile := filepath.Join(t.TempDir(), "test_large.txt")
+		largeData := make([]byte, 1024*1024) // 1MB
+		for i := range largeData {
+			largeData[i] = byte(i % 256)
+		}
+
+		writeOp := WriteFile(largeData)
+		result := writeOp(tempFile)(ctx)()
+
+		assert.True(t, E.IsRight(result))
+
+		// Verify file content
+		content, err := os.ReadFile(tempFile)
+		assert.NoError(t, err)
+		assert.Equal(t, largeData, content)
+	})
+
+	t.Run("Failure - invalid path", func(t *testing.T) {
+		invalidPath := filepath.Join(t.TempDir(), "nonexistent", "test.txt")
+		testData := []byte("test")
+
+		writeOp := WriteFile(testData)
+		result := writeOp(invalidPath)(ctx)()
+
+		assert.True(t, E.IsLeft(result))
+	})
+
+	t.Run("Success - writes binary data", func(t *testing.T) {
+		tempFile := filepath.Join(t.TempDir(), "test_binary.bin")
+		binaryData := []byte{0x00, 0x01, 0x02, 0xFF, 0xFE, 0xFD}
+
+		writeOp := WriteFile(binaryData)
+		result := writeOp(tempFile)(ctx)()
+
+		assert.True(t, E.IsRight(result))
+
+		// Verify binary content
+		content, err := os.ReadFile(tempFile)
+		assert.NoError(t, err)
+		assert.Equal(t, binaryData, content)
+	})
+
+	t.Run("Integration - write then read", func(t *testing.T) {
+		tempFile := filepath.Join(t.TempDir(), "test_roundtrip.txt")
+		testData := []byte("Round trip test data")
+
+		// Write data
+		writeOp := WriteFile(testData)
+		writeResult := writeOp(tempFile)(ctx)()
+		assert.True(t, E.IsRight(writeResult))
+
+		// Read data back
+		readOp := ReadFile(tempFile)
+		readResult := readOp(ctx)()
+		assert.True(t, E.IsRight(readResult))
+
+		// Verify data matches
+		E.MonadFold(readResult,
+			func(err error) []byte { t.Fatalf("Unexpected error: %v", err); return nil },
+			func(data []byte) []byte {
+				assert.Equal(t, testData, data)
+				return data
+			},
+		)
+	})
+
+	t.Run("Composition with Map", func(t *testing.T) {
+		tempFile := filepath.Join(t.TempDir(), "test_compose.txt")
+		testData := []byte("test data")
+
+		// Write and transform result
+		pipeline := F.Pipe1(
+			WriteFile(testData)(tempFile),
+			R.Map(func(data []byte) int { return len(data) }),
+		)
+
+		result := pipeline(ctx)()
+		assert.True(t, E.IsRight(result))
+
+		E.MonadFold(result,
+			func(err error) int { t.Fatalf("Unexpected error: %v", err); return 0 },
+			func(length int) int {
+				assert.Equal(t, len(testData), length)
+				return length
+			},
+		)
+	})
+
+	t.Run("Context cancellation during write", func(t *testing.T) {
+		cancelCtx, cancel := context.WithCancel(context.Background())
+		cancel() // Cancel immediately
+
+		tempFile := filepath.Join(t.TempDir(), "test_cancel.txt")
+		testData := []byte("test")
+
+		writeOp := WriteFile(testData)
+		result := writeOp(tempFile)(cancelCtx)()
+
+		// Note: The actual write may complete before cancellation is checked
+		// This test verifies the pattern works with cancelled contexts
+		_ = result
+	})
+}

v2/effect/common_test.go

@@ -26,7 +26,7 @@ type TestContext struct {
 
 // runEffect is a helper function to run an effect with a context and return the result
 func runEffect[C, A any](eff Effect[C, A], ctx C) (A, error) {
-	ioResult := Provide[C, A](ctx)(eff)
+	ioResult := Provide[A](ctx)(eff)
 	readerResult := RunSync(ioResult)
 	return readerResult(context.Background())
 }

v2/effect/dependencies.go

@@ -51,7 +51,7 @@ import (
 //	)(dbEffect)
 //
 //go:inline
-func Local[C1, C2, A any](acc Reader[C1, C2]) Kleisli[C1, Effect[C2, A], A] {
+func Local[A, C1, C2 any](acc Reader[C1, C2]) Kleisli[C1, Effect[C2, A], A] {
 	return readerreaderioresult.Local[A](acc)
 }
 
@@ -73,7 +73,7 @@ func Local[C1, C2, A any](acc Reader[C1, C2]) Kleisli[C1, Effect[C2, A], A] {
 //   - Kleisli[C1, Effect[C2, A], A]: A function that adapts the effect to use C1
 //
 //go:inline
-func Contramap[C1, C2, A any](acc Reader[C1, C2]) Kleisli[C1, Effect[C2, A], A] {
+func Contramap[A, C1, C2 any](acc Reader[C1, C2]) Kleisli[C1, Effect[C2, A], A] {
 	return readerreaderioresult.Local[A](acc)
 }
 

v2/effect/dependencies_test.go

@@ -44,11 +44,11 @@ func TestLocal(t *testing.T) {
 		}
 
 		// Apply Local to transform the context
-		kleisli := Local[OuterContext, InnerContext, string](accessor)
+		kleisli := Local[string](accessor)
 		outerEffect := kleisli(innerEffect)
 
 		// Run with OuterContext
-		ioResult := Provide[OuterContext, string](OuterContext{
+		ioResult := Provide[string](OuterContext{
 			Value:  "test",
 			Number: 42,
 		})(outerEffect)
@@ -70,11 +70,11 @@ func TestLocal(t *testing.T) {
 			return InnerContext{Value: outer.Value + " transformed"}
 		}
 
-		kleisli := Local[OuterContext, InnerContext, string](accessor)
+		kleisli := Local[string](accessor)
 		outerEffect := kleisli(innerEffect)
 
 		// Run with OuterContext
-		ioResult := Provide[OuterContext, string](OuterContext{
+		ioResult := Provide[string](OuterContext{
 			Value:  "original",
 			Number: 100,
 		})(outerEffect)
@@ -93,10 +93,10 @@ func TestLocal(t *testing.T) {
 			return InnerContext{Value: outer.Value}
 		}
 
-		kleisli := Local[OuterContext, InnerContext, string](accessor)
+		kleisli := Local[string](accessor)
 		outerEffect := kleisli(innerEffect)
 
-		ioResult := Provide[OuterContext, string](OuterContext{
+		ioResult := Provide[string](OuterContext{
 			Value:  "test",
 			Number: 42,
 		})(outerEffect)
@@ -122,12 +122,12 @@ func TestLocal(t *testing.T) {
 		level3Effect := Of[Level3]("deep result")
 
 		// Transform Level2 -> Level3
-		local23 := Local[Level2, Level3, string](func(l2 Level2) Level3 {
+		local23 := Local[string](func(l2 Level2) Level3 {
 			return Level3{C: l2.B + "-c"}
 		})
 
 		// Transform Level1 -> Level2
-		local12 := Local[Level1, Level2, string](func(l1 Level1) Level2 {
+		local12 := Local[string](func(l1 Level1) Level2 {
 			return Level2{B: l1.A + "-b"}
 		})
 
@@ -136,7 +136,7 @@ func TestLocal(t *testing.T) {
 		level1Effect := local12(level2Effect)
 
 		// Run with Level1 context
-		ioResult := Provide[Level1, string](Level1{A: "a"})(level1Effect)
+		ioResult := Provide[string](Level1{A: "a"})(level1Effect)
 		readerResult := RunSync(ioResult)
 		result, err := readerResult(context.Background())
 
@@ -165,11 +165,11 @@ func TestLocal(t *testing.T) {
 			return app.DB
 		}
 
-		kleisli := Local[AppConfig, DatabaseConfig, string](accessor)
+		kleisli := Local[string](accessor)
 		appEffect := kleisli(dbEffect)
 
 		// Run with full AppConfig
-		ioResult := Provide[AppConfig, string](AppConfig{
+		ioResult := Provide[string](AppConfig{
 			DB: DatabaseConfig{
 				Host:     "localhost",
 				Port:     5432,
@@ -195,21 +195,21 @@ func TestContramap(t *testing.T) {
 		}
 
 		// Test Local
-		localKleisli := Local[OuterContext, InnerContext, int](accessor)
+		localKleisli := Local[int](accessor)
 		localEffect := localKleisli(innerEffect)
 
 		// Test Contramap
-		contramapKleisli := Contramap[OuterContext, InnerContext, int](accessor)
+		contramapKleisli := Contramap[int](accessor)
 		contramapEffect := contramapKleisli(innerEffect)
 
 		outerCtx := OuterContext{Value: "test", Number: 100}
 
 		// Run both
-		localIO := Provide[OuterContext, int](outerCtx)(localEffect)
+		localIO := Provide[int](outerCtx)(localEffect)
 		localReader := RunSync(localIO)
 		localResult, localErr := localReader(context.Background())
 
-		contramapIO := Provide[OuterContext, int](outerCtx)(contramapEffect)
+		contramapIO := Provide[int](outerCtx)(contramapEffect)
 		contramapReader := RunSync(contramapIO)
 		contramapResult, contramapErr := contramapReader(context.Background())
 
@@ -225,10 +225,10 @@ func TestContramap(t *testing.T) {
 			return InnerContext{Value: outer.Value + " modified"}
 		}
 
-		kleisli := Contramap[OuterContext, InnerContext, string](accessor)
+		kleisli := Contramap[string](accessor)
 		outerEffect := kleisli(innerEffect)
 
-		ioResult := Provide[OuterContext, string](OuterContext{
+		ioResult := Provide[string](OuterContext{
 			Value:  "original",
 			Number: 50,
 		})(outerEffect)
@@ -247,10 +247,10 @@ func TestContramap(t *testing.T) {
 			return InnerContext{Value: outer.Value}
 		}
 
-		kleisli := Contramap[OuterContext, InnerContext, int](accessor)
+		kleisli := Contramap[int](accessor)
 		outerEffect := kleisli(innerEffect)
 
-		ioResult := Provide[OuterContext, int](OuterContext{
+		ioResult := Provide[int](OuterContext{
 			Value:  "test",
 			Number: 42,
 		})(outerEffect)
@@ -278,12 +278,12 @@ func TestLocalAndContramapInteroperability(t *testing.T) {
 		effect3 := Of[Config3]("result")
 
 		// Use Local for first transformation
-		local23 := Local[Config2, Config3, string](func(c2 Config2) Config3 {
+		local23 := Local[string](func(c2 Config2) Config3 {
 			return Config3{Info: c2.Data}
 		})
 
 		// Use Contramap for second transformation
-		contramap12 := Contramap[Config1, Config2, string](func(c1 Config1) Config2 {
+		contramap12 := Contramap[string](func(c1 Config1) Config2 {
 			return Config2{Data: c1.Value}
 		})
 
@@ -292,7 +292,7 @@ func TestLocalAndContramapInteroperability(t *testing.T) {
 		effect1 := contramap12(effect2)
 
 		// Run
-		ioResult := Provide[Config1, string](Config1{Value: "test"})(effect1)
+		ioResult := Provide[string](Config1{Value: "test"})(effect1)
 		readerResult := RunSync(ioResult)
 		result, err := readerResult(context.Background())
 
@@ -326,7 +326,7 @@ func TestLocalEffectK(t *testing.T) {
 		appEffect := transform(dbEffect)
 
 		// Run with AppConfig
-		ioResult := Provide[AppConfig, string](AppConfig{
+		ioResult := Provide[string](AppConfig{
 			ConfigPath: "/etc/app.conf",
 		})(appEffect)
 		readerResult := RunSync(ioResult)
@@ -356,7 +356,7 @@ func TestLocalEffectK(t *testing.T) {
 		transform := LocalEffectK[string](failingTransform)
 		outerEffect := transform(innerEffect)
 
-		ioResult := Provide[OuterCtx, string](OuterCtx{Path: "test"})(outerEffect)
+		ioResult := Provide[string](OuterCtx{Path: "test"})(outerEffect)
 		readerResult := RunSync(ioResult)
 		_, err := readerResult(context.Background())
 
@@ -384,7 +384,7 @@ func TestLocalEffectK(t *testing.T) {
 		transformK := LocalEffectK[string](transform)
 		outerEffect := transformK(innerEffect)
 
-		ioResult := Provide[OuterCtx, string](OuterCtx{Path: "test"})(outerEffect)
+		ioResult := Provide[string](OuterCtx{Path: "test"})(outerEffect)
 		readerResult := RunSync(ioResult)
 		_, err := readerResult(context.Background())
 
@@ -417,7 +417,7 @@ func TestLocalEffectK(t *testing.T) {
 		transform := LocalEffectK[string](loadConfigEffect)
 		appEffect := transform(configEffect)
 
-		ioResult := Provide[AppContext, string](AppContext{
+		ioResult := Provide[string](AppContext{
 			ConfigFile: "config.json",
 		})(appEffect)
 		readerResult := RunSync(ioResult)
@@ -456,7 +456,7 @@ func TestLocalEffectK(t *testing.T) {
 		level1Effect := transform12(level2Effect)
 
 		// Run with Level1 context
-		ioResult := Provide[Level1, string](Level1{A: "a"})(level1Effect)
+		ioResult := Provide[string](Level1{A: "a"})(level1Effect)
 		readerResult := RunSync(ioResult)
 		result, err := readerResult(context.Background())
 
@@ -497,7 +497,7 @@ func TestLocalEffectK(t *testing.T) {
 		transform := LocalEffectK[string](transformWithContext)
 		appEffect := transform(dbEffect)
 
-		ioResult := Provide[AppConfig, string](AppConfig{
+		ioResult := Provide[string](AppConfig{
 			Environment: "prod",
 			DBHost:      "localhost",
 			DBPort:      5432,
@@ -534,14 +534,14 @@ func TestLocalEffectK(t *testing.T) {
 		outerEffect := transform(innerEffect)
 
 		// Test with invalid config
-		ioResult := Provide[RawConfig, string](RawConfig{APIKey: ""})(outerEffect)
+		ioResult := Provide[string](RawConfig{APIKey: ""})(outerEffect)
 		readerResult := RunSync(ioResult)
 		_, err := readerResult(context.Background())
 
 		assert.Error(t, err)
 
 		// Test with valid config
-		ioResult2 := Provide[RawConfig, string](RawConfig{APIKey: "valid-key"})(outerEffect)
+		ioResult2 := Provide[string](RawConfig{APIKey: "valid-key"})(outerEffect)
 		readerResult2 := RunSync(ioResult2)
 		result, err2 := readerResult2(context.Background())
 
@@ -569,7 +569,7 @@ func TestLocalEffectK(t *testing.T) {
 		})
 
 		// Use Local for second transformation (pure)
-		local12 := Local[Level1, Level2, string](func(l1 Level1) Level2 {
+		local12 := Local[string](func(l1 Level1) Level2 {
 			return Level2{Data: l1.Value}
 		})
 
@@ -578,7 +578,7 @@ func TestLocalEffectK(t *testing.T) {
 		effect1 := local12(effect2)
 
 		// Run
-		ioResult := Provide[Level1, string](Level1{Value: "test"})(effect1)
+		ioResult := Provide[string](Level1{Value: "test"})(effect1)
 		readerResult := RunSync(ioResult)
 		result, err := readerResult(context.Background())
 
@@ -610,7 +610,7 @@ func TestLocalEffectK(t *testing.T) {
 		transform := LocalEffectK[int](complexTransform)
 		outerEffect := transform(innerEffect)
 
-		ioResult := Provide[OuterCtx, int](OuterCtx{Multiplier: 3})(outerEffect)
+		ioResult := Provide[int](OuterCtx{Multiplier: 3})(outerEffect)
 		readerResult := RunSync(ioResult)
 		result, err := readerResult(context.Background())
 

v2/effect/effect.go

@@ -20,6 +20,7 @@ import (
 	"github.com/IBM/fp-go/v2/context/readerreaderioresult"
 	"github.com/IBM/fp-go/v2/function"
 	"github.com/IBM/fp-go/v2/internal/fromreader"
+	"github.com/IBM/fp-go/v2/io"
 	"github.com/IBM/fp-go/v2/reader"
 	"github.com/IBM/fp-go/v2/readerio"
 	"github.com/IBM/fp-go/v2/result"
@@ -59,6 +60,11 @@ func FromThunk[C, A any](f Thunk[A]) Effect[C, A] {
 	return reader.Of[C](f)
 }
 
+//go:inline
+func FromResult[C, A any](r Result[A]) Effect[C, A] {
+	return readerreaderioresult.FromEither[C](r)
+}
+
 // Succeed creates a successful Effect that produces the given value.
 // This is the primary way to lift a pure value into the Effect context.
 //
@@ -187,10 +193,126 @@ func Map[C, A, B any](f func(A) B) Operator[C, A, B] {
 //		return effect.Of[MyContext](strconv.Itoa(x * 2))
 //	})(eff)
 //	// chained produces "84"
+//
+//go:inline
 func Chain[C, A, B any](f Kleisli[C, A, B]) Operator[C, A, B] {
 	return readerreaderioresult.Chain(f)
 }
 
+//go:inline
+func ChainFirst[C, A, B any](f Kleisli[C, A, B]) Operator[C, A, A] {
+	return readerreaderioresult.ChainFirst(f)
+}
+
+// ChainIOK chains an effect with a function that returns an IO action.
+// This is useful for integrating IO-based computations (synchronous side effects)
+// into effect chains. The IO action is automatically lifted into the Effect context.
+//
+// # Type Parameters
+//
+//   - C: The context type required by the effect
+//   - A: The input value type
+//   - B: The output value type
+//
+// # Parameters
+//
+//   - f: A function that takes A and returns IO[B]
+//
+// # Returns
+//
+//   - Operator[C, A, B]: A function that chains the IO-returning function with the effect
+//
+// # Example
+//
+//	performIO := func(n int) io.IO[string] {
+//	    return func() string {
+//	        // Perform synchronous side effect
+//	        return fmt.Sprintf("Value: %d", n)
+//	    }
+//	}
+//
+//	eff := effect.Of[MyContext](42)
+//	chained := effect.ChainIOK[MyContext](performIO)(eff)
+//	// chained produces "Value: 42"
+//
+//go:inline
+func ChainIOK[C, A, B any](f io.Kleisli[A, B]) Operator[C, A, B] {
+	return readerreaderioresult.ChainIOK[C](f)
+}
+
+// ChainFirstIOK chains an effect with a function that returns an IO action,
+// but discards the result and returns the original value.
+// This is useful for performing side effects (like logging) without changing the value.
+//
+// # Type Parameters
+//
+//   - C: The context type required by the effect
+//   - A: The value type (preserved)
+//   - B: The type produced by the IO action (discarded)
+//
+// # Parameters
+//
+//   - f: A function that takes A and returns IO[B] for side effects
+//
+// # Returns
+//
+//   - Operator[C, A, A]: A function that executes the IO action but preserves the original value
+//
+// # Example
+//
+//	logValue := func(n int) io.IO[any] {
+//	    return func() any {
+//	        fmt.Printf("Processing: %d\n", n)
+//	        return nil
+//	    }
+//	}
+//
+//	eff := effect.Of[MyContext](42)
+//	logged := effect.ChainFirstIOK[MyContext](logValue)(eff)
+//	// Prints "Processing: 42" but still produces 42
+//
+//go:inline
+func ChainFirstIOK[C, A, B any](f io.Kleisli[A, B]) Operator[C, A, A] {
+	return readerreaderioresult.ChainFirstIOK[C](f)
+}
+
+// TapIOK is an alias for ChainFirstIOK.
+// It chains an effect with a function that returns an IO action for side effects,
+// but preserves the original value. This is useful for logging, debugging, or
+// performing actions without changing the result.
+//
+// # Type Parameters
+//
+//   - C: The context type required by the effect
+//   - A: The value type (preserved)
+//   - B: The type produced by the IO action (discarded)
+//
+// # Parameters
+//
+//   - f: A function that takes A and returns IO[B] for side effects
+//
+// # Returns
+//
+//   - Operator[C, A, A]: A function that executes the IO action but preserves the original value
+//
+// # Example
+//
+//	logValue := func(n int) io.IO[any] {
+//	    return func() any {
+//	        fmt.Printf("Value: %d\n", n)
+//	        return nil
+//	    }
+//	}
+//
+//	eff := effect.Of[MyContext](42)
+//	tapped := effect.TapIOK[MyContext](logValue)(eff)
+//	// Prints "Value: 42" but still produces 42
+//
+//go:inline
+func TapIOK[C, A, B any](f io.Kleisli[A, B]) Operator[C, A, A] {
+	return readerreaderioresult.ChainFirstIOK[C](f)
+}
+
 // Ap applies a function wrapped in an Effect to a value wrapped in an Effect.
 // This is the applicative apply operation, useful for applying effects in parallel.
 //

v2/effect/effect_additional_test.go

@@ -0,0 +1,649 @@
+// Copyright (c) 2023 - 2025 IBM Corp.
+// All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package effect
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"strconv"
+	"testing"
+
+	F "github.com/IBM/fp-go/v2/function"
+	"github.com/IBM/fp-go/v2/io"
+	"github.com/IBM/fp-go/v2/reader"
+	"github.com/IBM/fp-go/v2/result"
+	"github.com/stretchr/testify/assert"
+)
+
+// TestSucceed tests the Succeed function
+func TestSucceed_Success(t *testing.T) {
+	t.Run("creates successful effect with int", func(t *testing.T) {
+		eff := Succeed[TestConfig](42)
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Of(42), outcome)
+	})
+
+	t.Run("creates successful effect with string", func(t *testing.T) {
+		eff := Succeed[TestConfig]("hello")
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Of("hello"), outcome)
+	})
+
+	t.Run("creates successful effect with zero value", func(t *testing.T) {
+		eff := Succeed[TestConfig](0)
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Of(0), outcome)
+	})
+}
+
+// TestFail tests the Fail function
+func TestFail_Failure(t *testing.T) {
+	t.Run("creates failed effect with error", func(t *testing.T) {
+		testErr := errors.New("test error")
+		eff := Fail[TestConfig, int](testErr)
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Left[int](testErr), outcome)
+	})
+
+	t.Run("preserves error message", func(t *testing.T) {
+		testErr := errors.New("specific error message")
+		eff := Fail[TestConfig, string](testErr)
+		outcome := eff(testConfig)(context.Background())()
+		assert.True(t, result.IsLeft(outcome))
+		extractedErr := result.MonadFold(outcome,
+			F.Identity[error],
+			func(string) error { return nil },
+		)
+		assert.Equal(t, testErr, extractedErr)
+	})
+}
+
+// TestOf tests the Of function
+func TestOf_Success(t *testing.T) {
+	t.Run("creates successful effect with value", func(t *testing.T) {
+		eff := Of[TestConfig](100)
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Of(100), outcome)
+	})
+
+	t.Run("is equivalent to Succeed", func(t *testing.T) {
+		value := "test"
+		eff1 := Of[TestConfig](value)
+		eff2 := Succeed[TestConfig](value)
+		outcome1 := eff1(testConfig)(context.Background())()
+		outcome2 := eff2(testConfig)(context.Background())()
+		assert.Equal(t, outcome1, outcome2)
+	})
+}
+
+// TestMap tests the Map function
+func TestMap_Success(t *testing.T) {
+	t.Run("transforms success value", func(t *testing.T) {
+		eff := F.Pipe1(
+			Of[TestConfig](42),
+			Map[TestConfig](func(x int) int { return x * 2 }),
+		)
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Of(84), outcome)
+	})
+
+	t.Run("transforms type", func(t *testing.T) {
+		eff := F.Pipe1(
+			Of[TestConfig](42),
+			Map[TestConfig](func(x int) string { return strconv.Itoa(x) }),
+		)
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Of("42"), outcome)
+	})
+
+	t.Run("chains multiple maps", func(t *testing.T) {
+		eff := F.Pipe2(
+			Of[TestConfig](10),
+			Map[TestConfig](func(x int) int { return x + 5 }),
+			Map[TestConfig](func(x int) int { return x * 2 }),
+		)
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Of(30), outcome)
+	})
+}
+
+func TestMap_Failure(t *testing.T) {
+	t.Run("propagates error unchanged", func(t *testing.T) {
+		testErr := errors.New("test error")
+		eff := F.Pipe1(
+			Fail[TestConfig, int](testErr),
+			Map[TestConfig](func(x int) int { return x * 2 }),
+		)
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Left[int](testErr), outcome)
+	})
+}
+
+// TestChain tests the Chain function
+func TestChain_Success(t *testing.T) {
+	t.Run("sequences two effects", func(t *testing.T) {
+		eff := F.Pipe1(
+			Of[TestConfig](42),
+			Chain(func(x int) Effect[TestConfig, string] {
+				return Of[TestConfig](strconv.Itoa(x))
+			}),
+		)
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Of("42"), outcome)
+	})
+
+	t.Run("chains multiple effects", func(t *testing.T) {
+		eff := F.Pipe2(
+			Of[TestConfig](10),
+			Chain(func(x int) Effect[TestConfig, int] {
+				return Of[TestConfig](x + 5)
+			}),
+			Chain(func(x int) Effect[TestConfig, int] {
+				return Of[TestConfig](x * 2)
+			}),
+		)
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Of(30), outcome)
+	})
+}
+
+func TestChain_Failure(t *testing.T) {
+	t.Run("propagates error from first effect", func(t *testing.T) {
+		testErr := errors.New("first error")
+		eff := F.Pipe1(
+			Fail[TestConfig, int](testErr),
+			Chain(func(x int) Effect[TestConfig, string] {
+				return Of[TestConfig]("should not execute")
+			}),
+		)
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Left[string](testErr), outcome)
+	})
+
+	t.Run("propagates error from second effect", func(t *testing.T) {
+		testErr := errors.New("second error")
+		eff := F.Pipe1(
+			Of[TestConfig](42),
+			Chain(func(x int) Effect[TestConfig, string] {
+				return Fail[TestConfig, string](testErr)
+			}),
+		)
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Left[string](testErr), outcome)
+	})
+}
+
+// TestChainIOK tests the ChainIOK function
+func TestChainIOK_Success(t *testing.T) {
+	t.Run("chains with IO action", func(t *testing.T) {
+		counter := 0
+		eff := F.Pipe1(
+			Of[TestConfig](42),
+			ChainIOK[TestConfig](func(x int) io.IO[string] {
+				return func() string {
+					counter++
+					return fmt.Sprintf("Value: %d", x)
+				}
+			}),
+		)
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Of("Value: 42"), outcome)
+		assert.Equal(t, 1, counter)
+	})
+
+	t.Run("chains multiple IO actions", func(t *testing.T) {
+		log := []string{}
+		eff := F.Pipe2(
+			Of[TestConfig](10),
+			ChainIOK[TestConfig](func(x int) io.IO[int] {
+				return func() int {
+					log = append(log, "first")
+					return x + 5
+				}
+			}),
+			ChainIOK[TestConfig](func(x int) io.IO[int] {
+				return func() int {
+					log = append(log, "second")
+					return x * 2
+				}
+			}),
+		)
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Of(30), outcome)
+		assert.Equal(t, []string{"first", "second"}, log)
+	})
+}
+
+func TestChainIOK_Failure(t *testing.T) {
+	t.Run("propagates error from previous effect", func(t *testing.T) {
+		testErr := errors.New("test error")
+		executed := false
+		eff := F.Pipe1(
+			Fail[TestConfig, int](testErr),
+			ChainIOK[TestConfig](func(x int) io.IO[string] {
+				return func() string {
+					executed = true
+					return "should not execute"
+				}
+			}),
+		)
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Left[string](testErr), outcome)
+		assert.False(t, executed)
+	})
+}
+
+// TestChainFirstIOK tests the ChainFirstIOK function
+func TestChainFirstIOK_Success(t *testing.T) {
+	t.Run("executes IO but preserves value", func(t *testing.T) {
+		log := []string{}
+		eff := F.Pipe1(
+			Of[TestConfig](42),
+			ChainFirstIOK[TestConfig](func(x int) io.IO[any] {
+				return func() any {
+					log = append(log, fmt.Sprintf("logged: %d", x))
+					return nil
+				}
+			}),
+		)
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Of(42), outcome)
+		assert.Equal(t, []string{"logged: 42"}, log)
+	})
+
+	t.Run("chains multiple side effects", func(t *testing.T) {
+		log := []string{}
+		eff := F.Pipe2(
+			Of[TestConfig](10),
+			ChainFirstIOK[TestConfig](func(x int) io.IO[any] {
+				return func() any {
+					log = append(log, "first")
+					return nil
+				}
+			}),
+			ChainFirstIOK[TestConfig](func(x int) io.IO[any] {
+				return func() any {
+					log = append(log, "second")
+					return nil
+				}
+			}),
+		)
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Of(10), outcome)
+		assert.Equal(t, []string{"first", "second"}, log)
+	})
+}
+
+func TestChainFirstIOK_Failure(t *testing.T) {
+	t.Run("propagates error without executing IO", func(t *testing.T) {
+		testErr := errors.New("test error")
+		executed := false
+		eff := F.Pipe1(
+			Fail[TestConfig, int](testErr),
+			ChainFirstIOK[TestConfig](func(x int) io.IO[any] {
+				return func() any {
+					executed = true
+					return nil
+				}
+			}),
+		)
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Left[int](testErr), outcome)
+		assert.False(t, executed)
+	})
+}
+
+// TestTapIOK tests the TapIOK function
+func TestTapIOK_Success(t *testing.T) {
+	t.Run("executes IO but preserves value", func(t *testing.T) {
+		log := []string{}
+		eff := F.Pipe1(
+			Of[TestConfig](42),
+			TapIOK[TestConfig](func(x int) io.IO[any] {
+				return func() any {
+					log = append(log, fmt.Sprintf("tapped: %d", x))
+					return nil
+				}
+			}),
+		)
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Of(42), outcome)
+		assert.Equal(t, []string{"tapped: 42"}, log)
+	})
+
+	t.Run("is equivalent to ChainFirstIOK", func(t *testing.T) {
+		log1 := []string{}
+		log2 := []string{}
+
+		eff1 := F.Pipe1(
+			Of[TestConfig](10),
+			TapIOK[TestConfig](func(x int) io.IO[any] {
+				return func() any {
+					log1 = append(log1, "tap")
+					return nil
+				}
+			}),
+		)
+
+		eff2 := F.Pipe1(
+			Of[TestConfig](10),
+			ChainFirstIOK[TestConfig](func(x int) io.IO[any] {
+				return func() any {
+					log2 = append(log2, "tap")
+					return nil
+				}
+			}),
+		)
+
+		outcome1 := eff1(testConfig)(context.Background())()
+		outcome2 := eff2(testConfig)(context.Background())()
+
+		assert.Equal(t, outcome1, outcome2)
+		assert.Equal(t, log1, log2)
+	})
+}
+
+func TestTapIOK_Failure(t *testing.T) {
+	t.Run("propagates error without executing IO", func(t *testing.T) {
+		testErr := errors.New("test error")
+		executed := false
+		eff := F.Pipe1(
+			Fail[TestConfig, int](testErr),
+			TapIOK[TestConfig](func(x int) io.IO[any] {
+				return func() any {
+					executed = true
+					return nil
+				}
+			}),
+		)
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Left[int](testErr), outcome)
+		assert.False(t, executed)
+	})
+}
+
+// TestChainResultK tests the ChainResultK function
+func TestChainResultK_Success(t *testing.T) {
+	t.Run("chains with Result-returning function", func(t *testing.T) {
+		parseIntResult := result.Eitherize1(strconv.Atoi)
+		eff := F.Pipe1(
+			Of[TestConfig]("42"),
+			ChainResultK[TestConfig](parseIntResult),
+		)
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Of(42), outcome)
+	})
+
+	t.Run("chains multiple Result operations", func(t *testing.T) {
+		parseIntResult := result.Eitherize1(strconv.Atoi)
+		eff := F.Pipe2(
+			Of[TestConfig]("10"),
+			ChainResultK[TestConfig](parseIntResult),
+			ChainResultK[TestConfig](func(x int) result.Result[string] {
+				return result.Of(fmt.Sprintf("Value: %d", x*2))
+			}),
+		)
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Of("Value: 20"), outcome)
+	})
+}
+
+func TestChainResultK_Failure(t *testing.T) {
+	t.Run("propagates error from previous effect", func(t *testing.T) {
+		testErr := errors.New("test error")
+		parseIntResult := result.Eitherize1(strconv.Atoi)
+		eff := F.Pipe1(
+			Fail[TestConfig, string](testErr),
+			ChainResultK[TestConfig](parseIntResult),
+		)
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Left[int](testErr), outcome)
+	})
+
+	t.Run("propagates error from Result function", func(t *testing.T) {
+		parseIntResult := result.Eitherize1(strconv.Atoi)
+		eff := F.Pipe1(
+			Of[TestConfig]("not a number"),
+			ChainResultK[TestConfig](parseIntResult),
+		)
+		outcome := eff(testConfig)(context.Background())()
+		assert.True(t, result.IsLeft(outcome))
+	})
+}
+
+// TestAp tests the Ap function
+func TestAp_Success(t *testing.T) {
+	t.Run("applies function effect to value effect", func(t *testing.T) {
+		fnEff := Of[TestConfig](func(x int) int { return x * 2 })
+		valEff := Of[TestConfig](21)
+		eff := Ap[int](valEff)(fnEff)
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Of(42), outcome)
+	})
+
+	t.Run("applies function with different types", func(t *testing.T) {
+		fnEff := Of[TestConfig](func(x int) string { return strconv.Itoa(x) })
+		valEff := Of[TestConfig](42)
+		eff := Ap[string](valEff)(fnEff)
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Of("42"), outcome)
+	})
+}
+
+func TestAp_Failure(t *testing.T) {
+	t.Run("propagates error from function effect", func(t *testing.T) {
+		testErr := errors.New("function error")
+		fnEff := Fail[TestConfig, func(int) int](testErr)
+		valEff := Of[TestConfig](42)
+		eff := Ap[int](valEff)(fnEff)
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Left[int](testErr), outcome)
+	})
+
+	t.Run("propagates error from value effect", func(t *testing.T) {
+		testErr := errors.New("value error")
+		fnEff := Of[TestConfig](func(x int) int { return x * 2 })
+		valEff := Fail[TestConfig, int](testErr)
+		eff := Ap[int](valEff)(fnEff)
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Left[int](testErr), outcome)
+	})
+}
+
+// TestSuspend tests the Suspend function
+func TestSuspend_Success(t *testing.T) {
+	t.Run("delays evaluation of effect", func(t *testing.T) {
+		counter := 0
+		eff := Suspend(func() Effect[TestConfig, int] {
+			counter++
+			return Of[TestConfig](42)
+		})
+		assert.Equal(t, 0, counter, "should not evaluate immediately")
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, 1, counter, "should evaluate when run")
+		assert.Equal(t, result.Of(42), outcome)
+	})
+
+	t.Run("enables recursive effects", func(t *testing.T) {
+		var factorial func(int) Effect[TestConfig, int]
+		factorial = func(n int) Effect[TestConfig, int] {
+			if n <= 1 {
+				return Of[TestConfig](1)
+			}
+			return Suspend(func() Effect[TestConfig, int] {
+				return F.Pipe1(
+					factorial(n-1),
+					Map[TestConfig](func(x int) int { return x * n }),
+				)
+			})
+		}
+
+		outcome := factorial(5)(testConfig)(context.Background())()
+		assert.Equal(t, result.Of(120), outcome)
+	})
+}
+
+// TestTap tests the Tap function
+func TestTap_Success(t *testing.T) {
+	t.Run("executes side effect but preserves value", func(t *testing.T) {
+		log := []string{}
+		eff := F.Pipe1(
+			Of[TestConfig](42),
+			Tap(func(x int) Effect[TestConfig, any] {
+				log = append(log, fmt.Sprintf("tapped: %d", x))
+				return Of[TestConfig, any](nil)
+			}),
+		)
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Of(42), outcome)
+		assert.Equal(t, []string{"tapped: 42"}, log)
+	})
+
+	t.Run("chains multiple taps", func(t *testing.T) {
+		log := []string{}
+		eff := F.Pipe2(
+			Of[TestConfig](10),
+			Tap(func(x int) Effect[TestConfig, any] {
+				log = append(log, "first")
+				return Of[TestConfig, any](nil)
+			}),
+			Tap(func(x int) Effect[TestConfig, any] {
+				log = append(log, "second")
+				return Of[TestConfig, any](nil)
+			}),
+		)
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Of(10), outcome)
+		assert.Equal(t, []string{"first", "second"}, log)
+	})
+}
+
+func TestTap_Failure(t *testing.T) {
+	t.Run("propagates error without executing tap", func(t *testing.T) {
+		testErr := errors.New("test error")
+		executed := false
+		eff := F.Pipe1(
+			Fail[TestConfig, int](testErr),
+			Tap(func(x int) Effect[TestConfig, any] {
+				executed = true
+				return Of[TestConfig, any](nil)
+			}),
+		)
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Left[int](testErr), outcome)
+		assert.False(t, executed)
+	})
+}
+
+// TestTernary tests the Ternary function
+func TestTernary_Success(t *testing.T) {
+	t.Run("executes onTrue when predicate is true", func(t *testing.T) {
+		kleisli := Ternary(
+			func(x int) bool { return x > 10 },
+			func(x int) Effect[TestConfig, string] {
+				return Of[TestConfig]("large")
+			},
+			func(x int) Effect[TestConfig, string] {
+				return Of[TestConfig]("small")
+			},
+		)
+		outcome := kleisli(15)(testConfig)(context.Background())()
+		assert.Equal(t, result.Of("large"), outcome)
+	})
+
+	t.Run("executes onFalse when predicate is false", func(t *testing.T) {
+		kleisli := Ternary(
+			func(x int) bool { return x > 10 },
+			func(x int) Effect[TestConfig, string] {
+				return Of[TestConfig]("large")
+			},
+			func(x int) Effect[TestConfig, string] {
+				return Of[TestConfig]("small")
+			},
+		)
+		outcome := kleisli(5)(testConfig)(context.Background())()
+		assert.Equal(t, result.Of("small"), outcome)
+	})
+
+	t.Run("works with boundary value", func(t *testing.T) {
+		kleisli := Ternary(
+			func(x int) bool { return x >= 10 },
+			func(x int) Effect[TestConfig, string] {
+				return Of[TestConfig]("gte")
+			},
+			func(x int) Effect[TestConfig, string] {
+				return Of[TestConfig]("lt")
+			},
+		)
+		outcome := kleisli(10)(testConfig)(context.Background())()
+		assert.Equal(t, result.Of("gte"), outcome)
+	})
+}
+
+// TestRead tests the Read function
+func TestRead_Success(t *testing.T) {
+	t.Run("provides context to effect", func(t *testing.T) {
+		eff := Of[TestConfig](42)
+		thunk := Read[int](testConfig)(eff)
+		outcome := thunk(context.Background())()
+		assert.Equal(t, result.Of(42), outcome)
+	})
+
+	t.Run("converts effect to thunk", func(t *testing.T) {
+		eff := F.Pipe1(
+			Of[TestConfig](10),
+			Map[TestConfig](func(x int) int { return x * testConfig.Multiplier }),
+		)
+		thunk := Read[int](testConfig)(eff)
+		outcome := thunk(context.Background())()
+		assert.Equal(t, result.Of(30), outcome)
+	})
+
+	t.Run("works with different contexts", func(t *testing.T) {
+		cfg1 := TestConfig{Multiplier: 2, Prefix: "A", DatabaseURL: ""}
+		cfg2 := TestConfig{Multiplier: 5, Prefix: "B", DatabaseURL: ""}
+
+		// Create an effect that uses the context's Multiplier
+		eff := F.Pipe1(
+			Of[TestConfig](10),
+			ChainReaderK(func(x int) reader.Reader[TestConfig, int] {
+				return func(cfg TestConfig) int {
+					return x * cfg.Multiplier
+				}
+			}),
+		)
+
+		thunk1 := Read[int](cfg1)(eff)
+		thunk2 := Read[int](cfg2)(eff)
+
+		outcome1 := thunk1(context.Background())()
+		outcome2 := thunk2(context.Background())()
+
+		assert.Equal(t, result.Of(20), outcome1)
+		assert.Equal(t, result.Of(50), outcome2)
+	})
+}
+
+func TestRead_Failure(t *testing.T) {
+	t.Run("propagates error from effect", func(t *testing.T) {
+		testErr := errors.New("test error")
+		eff := Fail[TestConfig, int](testErr)
+		thunk := Read[int](testConfig)(eff)
+		outcome := thunk(context.Background())()
+		assert.Equal(t, result.Left[int](testErr), outcome)
+	})
+}

v2/effect/effect_test.go

@@ -641,8 +641,8 @@ func TestChainThunkK_Integration(t *testing.T) {
 
 		computation := F.Pipe3(
 			Of[TestConfig](5),
-			ChainReaderK[TestConfig](addMultiplier),
-			ChainReaderIOK[TestConfig](logValue),
+			ChainReaderK(addMultiplier),
+			ChainReaderIOK(logValue),
 			ChainThunkK[TestConfig](processThunk),
 		)
 		outcome := computation(testConfig)(context.Background())()

v2/effect/run.go

@@ -46,7 +46,7 @@ import (
 //	eff := effect.Of[MyContext](42)
 //	thunk := effect.Provide[MyContext, int](ctx)(eff)
 //	// thunk is now a ReaderIOResult[int] that can be run
-func Provide[C, A any](c C) func(Effect[C, A]) ReaderIOResult[A] {
+func Provide[A, C any](c C) func(Effect[C, A]) ReaderIOResult[A] {
 	return readerreaderioresult.Read[A](c)
 }
 

v2/effect/run_test.go

@@ -28,7 +28,7 @@ func TestProvide(t *testing.T) {
 		ctx := TestContext{Value: "test-value"}
 		eff := Of[TestContext]("result")
 
-		ioResult := Provide[TestContext, string](ctx)(eff)
+		ioResult := Provide[string](ctx)(eff)
 		readerResult := RunSync(ioResult)
 		result, err := readerResult(context.Background())
 
@@ -45,7 +45,7 @@ func TestProvide(t *testing.T) {
 		cfg := Config{Host: "localhost", Port: 8080}
 		eff := Of[Config]("connected")
 
-		ioResult := Provide[Config, string](cfg)(eff)
+		ioResult := Provide[string](cfg)(eff)
 		readerResult := RunSync(ioResult)
 		result, err := readerResult(context.Background())
 
@@ -58,7 +58,7 @@ func TestProvide(t *testing.T) {
 		ctx := TestContext{Value: "test"}
 		eff := Fail[TestContext, string](expectedErr)
 
-		ioResult := Provide[TestContext, string](ctx)(eff)
+		ioResult := Provide[string](ctx)(eff)
 		readerResult := RunSync(ioResult)
 		_, err := readerResult(context.Background())
 
@@ -74,7 +74,7 @@ func TestProvide(t *testing.T) {
 		ctx := SimpleContext{ID: 42}
 		eff := Of[SimpleContext](100)
 
-		ioResult := Provide[SimpleContext, int](ctx)(eff)
+		ioResult := Provide[int](ctx)(eff)
 		readerResult := RunSync(ioResult)
 		result, err := readerResult(context.Background())
 
@@ -89,7 +89,7 @@ func TestProvide(t *testing.T) {
 			return Of[TestContext]("result")
 		})(Of[TestContext](42))
 
-		ioResult := Provide[TestContext, string](ctx)(eff)
+		ioResult := Provide[string](ctx)(eff)
 		readerResult := RunSync(ioResult)
 		result, err := readerResult(context.Background())
 
@@ -104,7 +104,7 @@ func TestProvide(t *testing.T) {
 			return "mapped"
 		})(Of[TestContext](42))
 
-		ioResult := Provide[TestContext, string](ctx)(eff)
+		ioResult := Provide[string](ctx)(eff)
 		readerResult := RunSync(ioResult)
 		result, err := readerResult(context.Background())
 
@@ -118,7 +118,7 @@ func TestRunSync(t *testing.T) {
 		ctx := TestContext{Value: "test"}
 		eff := Of[TestContext](42)
 
-		ioResult := Provide[TestContext, int](ctx)(eff)
+		ioResult := Provide[int](ctx)(eff)
 		readerResult := RunSync(ioResult)
 		result, err := readerResult(context.Background())
 
@@ -130,7 +130,7 @@ func TestRunSync(t *testing.T) {
 		ctx := TestContext{Value: "test"}
 		eff := Of[TestContext]("hello")
 
-		ioResult := Provide[TestContext, string](ctx)(eff)
+		ioResult := Provide[string](ctx)(eff)
 		readerResult := RunSync(ioResult)
 
 		bgCtx := context.Background()
@@ -145,7 +145,7 @@ func TestRunSync(t *testing.T) {
 		ctx := TestContext{Value: "test"}
 		eff := Fail[TestContext, int](expectedErr)
 
-		ioResult := Provide[TestContext, int](ctx)(eff)
+		ioResult := Provide[int](ctx)(eff)
 		readerResult := RunSync(ioResult)
 		_, err := readerResult(context.Background())
 
@@ -162,7 +162,7 @@ func TestRunSync(t *testing.T) {
 			return Of[TestContext](x + 10)
 		})(Of[TestContext](5)))
 
-		ioResult := Provide[TestContext, int](ctx)(eff)
+		ioResult := Provide[int](ctx)(eff)
 		readerResult := RunSync(ioResult)
 		result, err := readerResult(context.Background())
 
@@ -174,7 +174,7 @@ func TestRunSync(t *testing.T) {
 		ctx := TestContext{Value: "test"}
 		eff := Of[TestContext](42)
 
-		ioResult := Provide[TestContext, int](ctx)(eff)
+		ioResult := Provide[int](ctx)(eff)
 		readerResult := RunSync(ioResult)
 
 		// Run multiple times
@@ -200,7 +200,7 @@ func TestRunSync(t *testing.T) {
 		user := User{Name: "Alice", Age: 30}
 		eff := Of[TestContext](user)
 
-		ioResult := Provide[TestContext, User](ctx)(eff)
+		ioResult := Provide[User](ctx)(eff)
 		readerResult := RunSync(ioResult)
 		result, err := readerResult(context.Background())
 
@@ -222,7 +222,7 @@ func TestProvideAndRunSyncIntegration(t *testing.T) {
 		eff := Of[AppConfig]("API call successful")
 
 		// Provide config and run
-		result, err := RunSync(Provide[AppConfig, string](cfg)(eff))(context.Background())
+		result, err := RunSync(Provide[string](cfg)(eff))(context.Background())
 
 		assert.NoError(t, err)
 		assert.Equal(t, "API call successful", result)
@@ -238,7 +238,7 @@ func TestProvideAndRunSyncIntegration(t *testing.T) {
 
 		eff := Fail[AppConfig, string](expectedErr)
 
-		_, err := RunSync(Provide[AppConfig, string](cfg)(eff))(context.Background())
+		_, err := RunSync(Provide[string](cfg)(eff))(context.Background())
 
 		assert.Error(t, err)
 		assert.Equal(t, expectedErr, err)
@@ -253,7 +253,7 @@ func TestProvideAndRunSyncIntegration(t *testing.T) {
 			return Of[TestContext](x * 2)
 		})(Of[TestContext](21)))
 
-		result, err := RunSync(Provide[TestContext, string](ctx)(eff))(context.Background())
+		result, err := RunSync(Provide[string](ctx)(eff))(context.Background())
 
 		assert.NoError(t, err)
 		assert.Equal(t, "final", result)
@@ -281,7 +281,7 @@ func TestProvideAndRunSyncIntegration(t *testing.T) {
 			return State{X: x}
 		})(Of[TestContext](10)))
 
-		result, err := RunSync(Provide[TestContext, State](ctx)(eff))(context.Background())
+		result, err := RunSync(Provide[State](ctx)(eff))(context.Background())
 
 		assert.NoError(t, err)
 		assert.Equal(t, 10, result.X)
@@ -300,11 +300,11 @@ func TestProvideAndRunSyncIntegration(t *testing.T) {
 		innerEff := Of[InnerCtx]("inner result")
 
 		// Transform context
-		transformedEff := Local[OuterCtx, InnerCtx, string](func(outer OuterCtx) InnerCtx {
+		transformedEff := Local[string](func(outer OuterCtx) InnerCtx {
 			return InnerCtx{Data: outer.Value + "-transformed"}
 		})(innerEff)
 
-		result, err := RunSync(Provide[OuterCtx, string](outerCtx)(transformedEff))(context.Background())
+		result, err := RunSync(Provide[string](outerCtx)(transformedEff))(context.Background())
 
 		assert.NoError(t, err)
 		assert.Equal(t, "inner result", result)
@@ -318,7 +318,7 @@ func TestProvideAndRunSyncIntegration(t *testing.T) {
 			return Of[TestContext](x * 2)
 		})(input)
 
-		result, err := RunSync(Provide[TestContext, []int](ctx)(eff))(context.Background())
+		result, err := RunSync(Provide[[]int](ctx)(eff))(context.Background())
 
 		assert.NoError(t, err)
 		assert.Equal(t, []int{2, 4, 6, 8, 10}, result)

v2/either/either_test.go

@@ -379,7 +379,7 @@ func TestMonadChainLeft(t *testing.T) {
 func TestChainLeft(t *testing.T) {
 	t.Run("Curried function transforms Left value", func(t *testing.T) {
 		// Create a reusable error handler
-		handleNotFound := ChainLeft[error, string](func(err error) Either[string, int] {
+		handleNotFound := ChainLeft(func(err error) Either[string, int] {
 			if err.Error() == "not found" {
 				return Right[string](0)
 			}
@@ -391,7 +391,7 @@ func TestChainLeft(t *testing.T) {
 	})
 
 	t.Run("Curried function with Right value", func(t *testing.T) {
-		handler := ChainLeft[error, string](func(err error) Either[string, int] {
+		handler := ChainLeft(func(err error) Either[string, int] {
 			return Left[int]("should not be called")
 		})
 
@@ -401,7 +401,7 @@ func TestChainLeft(t *testing.T) {
 
 	t.Run("Use in pipeline with Pipe", func(t *testing.T) {
 		// Create error transformer
-		toStringError := ChainLeft[int, string](func(code int) Either[string, string] {
+		toStringError := ChainLeft(func(code int) Either[string, string] {
 			return Left[string](fmt.Sprintf("Error: %d", code))
 		})
 
@@ -414,12 +414,12 @@ func TestChainLeft(t *testing.T) {
 
 	t.Run("Compose multiple ChainLeft operations", func(t *testing.T) {
 		// First handler: convert error to string
-		handler1 := ChainLeft[error, string](func(err error) Either[string, int] {
+		handler1 := ChainLeft(func(err error) Either[string, int] {
 			return Left[int](err.Error())
 		})
 
 		// Second handler: add prefix to string error
-		handler2 := ChainLeft[string, string](func(s string) Either[string, int] {
+		handler2 := ChainLeft(func(s string) Either[string, int] {
 			return Left[int]("Handled: " + s)
 		})
 

v2/monoid/types.go

@@ -0,0 +1,52 @@
+// Copyright (c) 2023 - 2025 IBM Corp.
+// All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package monoid
+
+import "github.com/IBM/fp-go/v2/function"
+
+// Void is an alias for function.Void, representing the unit type.
+//
+// The Void type (also known as Unit in functional programming) has exactly one value,
+// making it useful for representing the absence of meaningful information. It's similar
+// to void in other languages, but as a value rather than the absence of a value.
+//
+// This type alias is provided in the monoid package for convenience when working with
+// VoidMonoid and other monoid operations that may use the unit type.
+//
+// Common use cases:
+//   - As a return type for functions that perform side effects but don't return meaningful data
+//   - As a placeholder type parameter when a type is required but no data needs to be passed
+//   - In monoid operations where you need to track that operations occurred without caring about results
+//
+// See also:
+//   - function.Void: The underlying type definition
+//   - function.VOID: The single inhabitant of the Void type
+//   - VoidMonoid: A monoid instance for the Void type
+//
+// Example:
+//
+//	// Function that performs an action but returns no meaningful data
+//	func logMessage(msg string) Void {
+//	    fmt.Println(msg)
+//	    return function.VOID
+//	}
+//
+//	// Using Void in monoid operations
+//	m := VoidMonoid()
+//	result := m.Concat(function.VOID, function.VOID)  // function.VOID
+type (
+	Void = function.Void
+)

v2/monoid/void.go

@@ -0,0 +1,65 @@
+// Copyright (c) 2023 - 2025 IBM Corp.
+// All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package monoid
+
+import (
+	"github.com/IBM/fp-go/v2/function"
+	S "github.com/IBM/fp-go/v2/semigroup"
+)
+
+// VoidMonoid creates a Monoid for the Void (unit) type.
+//
+// The Void type has exactly one value (function.VOID), making it trivial to define
+// a monoid. This monoid uses the Last semigroup, which always returns the second
+// argument, though since all Void values are identical, the choice of semigroup
+// doesn't affect the result.
+//
+// This monoid is useful in contexts where:
+//   - A monoid instance is required but no meaningful data needs to be combined
+//   - You need to track that an operation occurred without caring about its result
+//   - Building generic abstractions that work with any monoid, including the trivial case
+//
+// # Monoid Laws
+//
+// The VoidMonoid satisfies all monoid laws trivially:
+//   - Associativity: Concat(Concat(x, y), z) = Concat(x, Concat(y, z)) - always VOID
+//   - Left Identity: Concat(Empty(), x) = x - always VOID
+//   - Right Identity: Concat(x, Empty()) = x - always VOID
+//
+// Returns:
+//   - A Monoid[Void] instance
+//
+// Example:
+//
+//	m := VoidMonoid()
+//	result := m.Concat(function.VOID, function.VOID)  // function.VOID
+//	empty := m.Empty()                                 // function.VOID
+//
+//	// Useful for tracking operations without data
+//	type Action = func() Void
+//	actions := []Action{
+//	    func() Void { fmt.Println("Action 1"); return function.VOID },
+//	    func() Void { fmt.Println("Action 2"); return function.VOID },
+//	}
+//	// Execute all actions and combine results
+//	results := A.Map(func(a Action) Void { return a() })(actions)
+//	_ = ConcatAll(m)(results)  // All actions executed, result is VOID
+func VoidMonoid() Monoid[Void] {
+	return MakeMonoid(
+		S.Last[Void]().Concat,
+		function.VOID,
+	)
+}

v2/monoid/void_test.go

@@ -0,0 +1,292 @@
+// Copyright (c) 2023 - 2025 IBM Corp.
+// All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package monoid
+
+import (
+	"testing"
+
+	"github.com/IBM/fp-go/v2/function"
+	"github.com/stretchr/testify/assert"
+)
+
+// TestVoidMonoid_Basic tests basic VoidMonoid functionality
+func TestVoidMonoid_Basic(t *testing.T) {
+	m := VoidMonoid()
+
+	// Test Empty returns VOID
+	empty := m.Empty()
+	assert.Equal(t, function.VOID, empty)
+
+	// Test Concat returns VOID (since all Void values are identical)
+	result := m.Concat(function.VOID, function.VOID)
+	assert.Equal(t, function.VOID, result)
+}
+
+// TestVoidMonoid_Laws verifies VoidMonoid satisfies monoid laws
+func TestVoidMonoid_Laws(t *testing.T) {
+	m := VoidMonoid()
+
+	// Since Void has only one value, we test with that value
+	v := function.VOID
+
+	// Left Identity: Concat(Empty(), x) = x
+	t.Run("left identity", func(t *testing.T) {
+		result := m.Concat(m.Empty(), v)
+		assert.Equal(t, v, result, "Left identity law failed")
+	})
+
+	// Right Identity: Concat(x, Empty()) = x
+	t.Run("right identity", func(t *testing.T) {
+		result := m.Concat(v, m.Empty())
+		assert.Equal(t, v, result, "Right identity law failed")
+	})
+
+	// Associativity: Concat(Concat(x, y), z) = Concat(x, Concat(y, z))
+	t.Run("associativity", func(t *testing.T) {
+		left := m.Concat(m.Concat(v, v), v)
+		right := m.Concat(v, m.Concat(v, v))
+		assert.Equal(t, left, right, "Associativity law failed")
+	})
+
+	// All results should be VOID
+	t.Run("all operations return VOID", func(t *testing.T) {
+		assert.Equal(t, function.VOID, m.Concat(v, v))
+		assert.Equal(t, function.VOID, m.Empty())
+		assert.Equal(t, function.VOID, m.Concat(m.Empty(), v))
+		assert.Equal(t, function.VOID, m.Concat(v, m.Empty()))
+	})
+}
+
+// TestVoidMonoid_ConcatAll tests combining multiple Void values
+func TestVoidMonoid_ConcatAll(t *testing.T) {
+	m := VoidMonoid()
+	concatAll := ConcatAll(m)
+
+	tests := []struct {
+		name     string
+		input    []Void
+		expected Void
+	}{
+		{
+			name:     "empty slice",
+			input:    []Void{},
+			expected: function.VOID,
+		},
+		{
+			name:     "single element",
+			input:    []Void{function.VOID},
+			expected: function.VOID,
+		},
+		{
+			name:     "multiple elements",
+			input:    []Void{function.VOID, function.VOID, function.VOID},
+			expected: function.VOID,
+		},
+		{
+			name:     "many elements",
+			input:    make([]Void, 100),
+			expected: function.VOID,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			// Initialize slice with VOID values
+			for i := range tt.input {
+				tt.input[i] = function.VOID
+			}
+			result := concatAll(tt.input)
+			assert.Equal(t, tt.expected, result)
+		})
+	}
+}
+
+// TestVoidMonoid_Fold tests the Fold function with VoidMonoid
+func TestVoidMonoid_Fold(t *testing.T) {
+	m := VoidMonoid()
+	fold := Fold(m)
+
+	// Fold should behave identically to ConcatAll
+	voids := []Void{function.VOID, function.VOID, function.VOID}
+	result := fold(voids)
+	assert.Equal(t, function.VOID, result)
+
+	// Empty fold
+	emptyResult := fold([]Void{})
+	assert.Equal(t, function.VOID, emptyResult)
+}
+
+// TestVoidMonoid_Reverse tests that Reverse doesn't affect VoidMonoid
+func TestVoidMonoid_Reverse(t *testing.T) {
+	m := VoidMonoid()
+	reversed := Reverse(m)
+
+	// Since all Void values are identical, reverse should have no effect
+	v := function.VOID
+
+	assert.Equal(t, m.Concat(v, v), reversed.Concat(v, v))
+	assert.Equal(t, m.Empty(), reversed.Empty())
+
+	// Test identity laws still hold
+	assert.Equal(t, v, reversed.Concat(reversed.Empty(), v))
+	assert.Equal(t, v, reversed.Concat(v, reversed.Empty()))
+}
+
+// TestVoidMonoid_ToSemigroup tests conversion to Semigroup
+func TestVoidMonoid_ToSemigroup(t *testing.T) {
+	m := VoidMonoid()
+	sg := ToSemigroup(m)
+
+	// Should work as a semigroup
+	result := sg.Concat(function.VOID, function.VOID)
+	assert.Equal(t, function.VOID, result)
+
+	// Verify it's the same underlying operation
+	assert.Equal(t, m.Concat(function.VOID, function.VOID), sg.Concat(function.VOID, function.VOID))
+}
+
+// TestVoidMonoid_FunctionMonoid tests VoidMonoid with FunctionMonoid
+func TestVoidMonoid_FunctionMonoid(t *testing.T) {
+	m := VoidMonoid()
+	funcMonoid := FunctionMonoid[string](m)
+
+	// Create functions that return Void
+	f1 := func(s string) Void { return function.VOID }
+	f2 := func(s string) Void { return function.VOID }
+
+	// Combine functions
+	combined := funcMonoid.Concat(f1, f2)
+
+	// Test combined function
+	result := combined("test")
+	assert.Equal(t, function.VOID, result)
+
+	// Test empty function
+	emptyFunc := funcMonoid.Empty()
+	assert.Equal(t, function.VOID, emptyFunc("anything"))
+}
+
+// TestVoidMonoid_PracticalUsage demonstrates practical usage patterns
+func TestVoidMonoid_PracticalUsage(t *testing.T) {
+	m := VoidMonoid()
+
+	// Simulate tracking that operations occurred without caring about results
+	type Action func() Void
+
+	actions := []Action{
+		func() Void { return function.VOID }, // Action 1
+		func() Void { return function.VOID }, // Action 2
+		func() Void { return function.VOID }, // Action 3
+	}
+
+	// Execute all actions and collect results
+	results := make([]Void, len(actions))
+	for i, action := range actions {
+		results[i] = action()
+	}
+
+	// Combine all results (all are VOID)
+	finalResult := ConcatAll(m)(results)
+	assert.Equal(t, function.VOID, finalResult)
+}
+
+// TestVoidMonoid_EdgeCases tests edge cases
+func TestVoidMonoid_EdgeCases(t *testing.T) {
+	m := VoidMonoid()
+
+	t.Run("multiple concatenations", func(t *testing.T) {
+		// Chain multiple Concat operations
+		result := m.Concat(
+			m.Concat(
+				m.Concat(function.VOID, function.VOID),
+				function.VOID,
+			),
+			function.VOID,
+		)
+		assert.Equal(t, function.VOID, result)
+	})
+
+	t.Run("concat with empty", func(t *testing.T) {
+		// Various combinations with Empty()
+		assert.Equal(t, function.VOID, m.Concat(m.Empty(), m.Empty()))
+		assert.Equal(t, function.VOID, m.Concat(m.Concat(m.Empty(), function.VOID), m.Empty()))
+	})
+
+	t.Run("large slice", func(t *testing.T) {
+		// Test with a large number of elements
+		largeSlice := make([]Void, 10000)
+		for i := range largeSlice {
+			largeSlice[i] = function.VOID
+		}
+		result := ConcatAll(m)(largeSlice)
+		assert.Equal(t, function.VOID, result)
+	})
+}
+
+// TestVoidMonoid_TypeSafety verifies type safety
+func TestVoidMonoid_TypeSafety(t *testing.T) {
+	m := VoidMonoid()
+
+	// Verify it implements Monoid interface
+	var _ Monoid[Void] = m
+
+	// Verify Empty returns correct type
+	empty := m.Empty()
+	var _ Void = empty
+
+	// Verify Concat returns correct type
+	result := m.Concat(function.VOID, function.VOID)
+	var _ Void = result
+}
+
+// BenchmarkVoidMonoid_Concat benchmarks the Concat operation
+func BenchmarkVoidMonoid_Concat(b *testing.B) {
+	m := VoidMonoid()
+	v := function.VOID
+
+	b.ResetTimer()
+	for b.Loop() {
+		_ = m.Concat(v, v)
+	}
+}
+
+// BenchmarkVoidMonoid_ConcatAll benchmarks combining multiple Void values
+func BenchmarkVoidMonoid_ConcatAll(b *testing.B) {
+	m := VoidMonoid()
+	concatAll := ConcatAll(m)
+
+	voids := make([]Void, 1000)
+	for i := range voids {
+		voids[i] = function.VOID
+	}
+
+	b.ResetTimer()
+	for b.Loop() {
+		_ = concatAll(voids)
+	}
+}
+
+// BenchmarkVoidMonoid_Empty benchmarks the Empty operation
+func BenchmarkVoidMonoid_Empty(b *testing.B) {
+	m := VoidMonoid()
+
+	b.ResetTimer()
+	for b.Loop() {
+		_ = m.Empty()
+	}
+}
+
+// Made with Bob

v2/optics/codec/alt_test.go

@@ -62,7 +62,7 @@ func TestMonadAltBasicFunctionality(t *testing.T) {
 
 		assert.True(t, either.IsRight(result), "should successfully decode with first codec")
 
-		value := either.GetOrElse(reader.Of[validation.Errors, string](""))(result)
+		value := either.GetOrElse(reader.Of[validation.Errors](""))(result)
 		assert.Equal(t, "HELLO", value)
 	})
 
@@ -105,7 +105,7 @@ func TestMonadAltBasicFunctionality(t *testing.T) {
 
 		assert.True(t, either.IsRight(result), "should successfully decode with second codec")
 
-		value := either.GetOrElse(reader.Of[validation.Errors, int](0))(result)
+		value := either.GetOrElse(reader.Of[validation.Errors](0))(result)
 		assert.Equal(t, -5, value)
 	})
 
@@ -302,19 +302,19 @@ func TestAltOperator(t *testing.T) {
 		// Test with "42" - should use base codec
 		result1 := pipeline.Decode("42")
 		assert.True(t, either.IsRight(result1))
-		value1 := either.GetOrElse(reader.Of[validation.Errors, int](0))(result1)
+		value1 := either.GetOrElse(reader.Of[validation.Errors](0))(result1)
 		assert.Equal(t, 42, value1)
 
 		// Test with "100" - should use fallback1
 		result2 := pipeline.Decode("100")
 		assert.True(t, either.IsRight(result2))
-		value2 := either.GetOrElse(reader.Of[validation.Errors, int](0))(result2)
+		value2 := either.GetOrElse(reader.Of[validation.Errors](0))(result2)
 		assert.Equal(t, 100, value2)
 
 		// Test with "999" - should use fallback2
 		result3 := pipeline.Decode("999")
 		assert.True(t, either.IsRight(result3))
-		value3 := either.GetOrElse(reader.Of[validation.Errors, int](0))(result3)
+		value3 := either.GetOrElse(reader.Of[validation.Errors](0))(result3)
 		assert.Equal(t, 999, value3)
 	})
 }
@@ -449,7 +449,7 @@ func TestAltRoundTrip(t *testing.T) {
 		decodeResult := altCodec.Decode(original)
 		require.True(t, either.IsRight(decodeResult))
 
-		decoded := either.GetOrElse(reader.Of[validation.Errors, string](""))(decodeResult)
+		decoded := either.GetOrElse(reader.Of[validation.Errors](""))(decodeResult)
 
 		// Encode
 		encoded := altCodec.Encode(decoded)
@@ -487,7 +487,7 @@ func TestAltRoundTrip(t *testing.T) {
 		decodeResult := altCodec.Decode(original)
 		require.True(t, either.IsRight(decodeResult))
 
-		decoded := either.GetOrElse(reader.Of[validation.Errors, string](""))(decodeResult)
+		decoded := either.GetOrElse(reader.Of[validation.Errors](""))(decodeResult)
 
 		// Encode (uses first codec's encoder, which is identity)
 		encoded := altCodec.Encode(decoded)
@@ -619,7 +619,7 @@ func TestAltMonoid(t *testing.T) {
 			result := combined.Decode("input")
 
 			assert.True(t, either.IsRight(result))
-			value := either.GetOrElse(reader.Of[validation.Errors, int](0))(result)
+			value := either.GetOrElse(reader.Of[validation.Errors](0))(result)
 			assert.Equal(t, 10, value, "first success should win")
 		})
 
@@ -628,7 +628,7 @@ func TestAltMonoid(t *testing.T) {
 			result := combined.Decode("42")
 
 			assert.True(t, either.IsRight(result))
-			value := either.GetOrElse(reader.Of[validation.Errors, int](0))(result)
+			value := either.GetOrElse(reader.Of[validation.Errors](0))(result)
 			assert.Equal(t, 42, value)
 		})
 
@@ -637,7 +637,7 @@ func TestAltMonoid(t *testing.T) {
 			result := combined.Decode("invalid")
 
 			assert.True(t, either.IsRight(result))
-			value := either.GetOrElse(reader.Of[validation.Errors, int](-1))(result)
+			value := either.GetOrElse(reader.Of[validation.Errors](-1))(result)
 			assert.Equal(t, 0, value, "should use default zero value")
 		})
 	})
@@ -768,21 +768,21 @@ func TestAltMonoid(t *testing.T) {
 		t.Run("uses primary when it succeeds", func(t *testing.T) {
 			result := combined.Decode("primary")
 			assert.True(t, either.IsRight(result))
-			value := either.GetOrElse(reader.Of[validation.Errors, string](""))(result)
+			value := either.GetOrElse(reader.Of[validation.Errors](""))(result)
 			assert.Equal(t, "from primary", value)
 		})
 
 		t.Run("uses secondary when primary fails", func(t *testing.T) {
 			result := combined.Decode("secondary")
 			assert.True(t, either.IsRight(result))
-			value := either.GetOrElse(reader.Of[validation.Errors, string](""))(result)
+			value := either.GetOrElse(reader.Of[validation.Errors](""))(result)
 			assert.Equal(t, "from secondary", value)
 		})
 
 		t.Run("uses default when both fail", func(t *testing.T) {
 			result := combined.Decode("other")
 			assert.True(t, either.IsRight(result))
-			value := either.GetOrElse(reader.Of[validation.Errors, string](""))(result)
+			value := either.GetOrElse(reader.Of[validation.Errors](""))(result)
 			assert.Equal(t, "default", value)
 		})
 	})
@@ -841,7 +841,7 @@ func TestAltMonoid(t *testing.T) {
 			result := combined.Decode("input")
 
 			assert.True(t, either.IsRight(result))
-			value := either.GetOrElse(reader.Of[validation.Errors, int](-1))(result)
+			value := either.GetOrElse(reader.Of[validation.Errors](-1))(result)
 			// Empty (0) comes first, so it wins
 			assert.Equal(t, 0, value)
 		})
@@ -852,7 +852,7 @@ func TestAltMonoid(t *testing.T) {
 			result := combined.Decode("input")
 
 			assert.True(t, either.IsRight(result))
-			value := either.GetOrElse(reader.Of[validation.Errors, int](-1))(result)
+			value := either.GetOrElse(reader.Of[validation.Errors](-1))(result)
 			assert.Equal(t, 10, value, "codec1 should win")
 		})
 
@@ -867,8 +867,8 @@ func TestAltMonoid(t *testing.T) {
 			assert.True(t, either.IsRight(resultLeft))
 			assert.True(t, either.IsRight(resultRight))
 
-			valueLeft := either.GetOrElse(reader.Of[validation.Errors, int](-1))(resultLeft)
-			valueRight := either.GetOrElse(reader.Of[validation.Errors, int](-1))(resultRight)
+			valueLeft := either.GetOrElse(reader.Of[validation.Errors](-1))(resultLeft)
+			valueRight := either.GetOrElse(reader.Of[validation.Errors](-1))(resultRight)
 
 			// Both should return 10 (first success)
 			assert.Equal(t, valueLeft, valueRight)

v2/optics/codec/bind.go

@@ -0,0 +1,299 @@
+// Copyright (c) 2023 - 2025 IBM Corp.
+// All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package codec
+
+import (
+	"fmt"
+
+	F "github.com/IBM/fp-go/v2/function"
+	"github.com/IBM/fp-go/v2/lazy"
+	"github.com/IBM/fp-go/v2/optics/codec/validate"
+	"github.com/IBM/fp-go/v2/option"
+	"github.com/IBM/fp-go/v2/reader"
+	"github.com/IBM/fp-go/v2/semigroup"
+)
+
+// ApSL creates an applicative sequencing operator for codecs using a lens.
+//
+// This function implements the "ApS" (Applicative Sequencing) pattern for codecs,
+// allowing you to build up complex codecs by combining a base codec with a field
+// accessed through a lens. It's particularly useful for building struct codecs
+// field-by-field in a composable way.
+//
+// The function combines:
+//   - Encoding: Extracts the field value using the lens, encodes it with fa, and
+//     combines it with the base encoding using the monoid
+//   - Validation: Validates the field using the lens and combines the validation
+//     with the base validation
+//
+// # Type Parameters
+//
+//   - S: The source struct type (what we're building a codec for)
+//   - T: The field type accessed by the lens
+//   - O: The output type for encoding (must have a monoid)
+//   - I: The input type for decoding
+//
+// # Parameters
+//
+//   - m: A Monoid[O] for combining encoded outputs
+//   - l: A Lens[S, T] that focuses on a specific field in S
+//   - fa: A Type[T, O, I] codec for the field type T
+//
+// # Returns
+//
+// An Operator[S, S, O, I] that transforms a base codec by adding the field
+// specified by the lens.
+//
+// # How It Works
+//
+// 1. **Encoding**: When encoding a value of type S:
+//   - Extract the field T using l.Get
+//   - Encode T to O using fa.Encode
+//   - Combine with the base encoding using the monoid
+//
+// 2. **Validation**: When validating input I:
+//   - Validate the field using fa.Validate through the lens
+//   - Combine with the base validation
+//
+// 3. **Type Checking**: Preserves the base type checker
+//
+// # Example
+//
+//	import (
+//	    "github.com/IBM/fp-go/v2/optics/codec"
+//	    "github.com/IBM/fp-go/v2/optics/lens"
+//	    S "github.com/IBM/fp-go/v2/string"
+//	)
+//
+//	type Person struct {
+//	    Name string
+//	    Age  int
+//	}
+//
+//	// Lenses for Person fields
+//	nameLens := lens.MakeLens(
+//	    func(p *Person) string { return p.Name },
+//	    func(p *Person, name string) *Person { p.Name = name; return p },
+//	)
+//
+//	// Build a Person codec field by field
+//	personCodec := F.Pipe1(
+//	    codec.Struct[Person]("Person"),
+//	    codec.ApSL(S.Monoid, nameLens, codec.String),
+//	    // ... add more fields
+//	)
+//
+// # Use Cases
+//
+//   - Building struct codecs incrementally
+//   - Composing codecs for nested structures
+//   - Creating type-safe serialization/deserialization
+//   - Implementing Do-notation style codec construction
+//
+// # Notes
+//
+//   - The monoid determines how encoded outputs are combined
+//   - The lens must be total (handle all cases safely)
+//   - This is typically used with other ApS functions to build complete codecs
+//   - The name is automatically generated for debugging purposes
+//
+// See also:
+//   - validate.ApSL: The underlying validation combinator
+//   - reader.ApplicativeMonoid: The monoid-based applicative instance
+//   - Lens: The optic for accessing struct fields
+func ApSL[S, T, O, I any](
+	m Monoid[O],
+	l Lens[S, T],
+	fa Type[T, O, I],
+) Operator[S, S, O, I] {
+	name := fmt.Sprintf("ApS[%s x %s]", l, fa)
+	rm := reader.ApplicativeMonoid[S](m)
+
+	encConcat := F.Pipe1(
+		F.Flow2(
+			l.Get,
+			fa.Encode,
+		),
+		semigroup.AppendTo(rm),
+	)
+
+	valConcat := validate.ApSL(l, fa.Validate)
+
+	return func(t Type[S, O, I]) Type[S, O, I] {
+
+		return MakeType(
+			name,
+			t.Is,
+			F.Pipe1(
+				t.Validate,
+				valConcat,
+			),
+			encConcat(t.Encode),
+		)
+	}
+}
+
+// ApSO creates an applicative sequencing operator for codecs using an optional.
+//
+// This function implements the "ApS" (Applicative Sequencing) pattern for codecs
+// with optional fields, allowing you to build up complex codecs by combining a base
+// codec with a field that may or may not be present. It's particularly useful for
+// building struct codecs with optional fields in a composable way.
+//
+// The function combines:
+//   - Encoding: Attempts to extract the optional field value, encodes it if present,
+//     and combines it with the base encoding using the monoid. If the field is absent,
+//     only the base encoding is used.
+//   - Validation: Validates the optional field and combines the validation with the
+//     base validation using applicative semantics (error accumulation).
+//
+// # Type Parameters
+//
+//   - S: The source struct type (what we're building a codec for)
+//   - T: The optional field type accessed by the optional
+//   - O: The output type for encoding (must have a monoid)
+//   - I: The input type for decoding
+//
+// # Parameters
+//
+//   - m: A Monoid[O] for combining encoded outputs
+//   - o: An Optional[S, T] that focuses on a field in S that may not exist
+//   - fa: A Type[T, O, I] codec for the optional field type T
+//
+// # Returns
+//
+// An Operator[S, S, O, I] that transforms a base codec by adding the optional field
+// specified by the optional.
+//
+// # How It Works
+//
+// 1. **Encoding**: When encoding a value of type S:
+//   - Try to extract the optional field T using o.GetOption
+//   - If present (Some(T)): Encode T to O using fa.Encode and combine with base using monoid
+//   - If absent (None): Return only the base encoding unchanged
+//
+// 2. **Validation**: When validating input I:
+//   - Validate the optional field using fa.Validate through o.Set
+//   - Combine with the base validation using applicative semantics
+//   - Accumulates all validation errors from both base and field
+//
+// 3. **Type Checking**: Preserves the base type checker
+//
+// # Difference from ApSL
+//
+// Unlike ApSL which works with required fields via Lens, ApSO handles optional fields:
+//   - ApSL: Field always exists, always encoded
+//   - ApSO: Field may not exist, only encoded when present
+//   - ApSO uses Optional.GetOption which returns Option[T]
+//   - ApSO gracefully handles missing fields without errors
+//
+// # Example
+//
+//	import (
+//	    "github.com/IBM/fp-go/v2/optics/codec"
+//	    "github.com/IBM/fp-go/v2/optics/optional"
+//	    S "github.com/IBM/fp-go/v2/string"
+//	)
+//
+//	type Person struct {
+//	    Name      string
+//	    Nickname  *string  // Optional field
+//	}
+//
+//	// Optional for Person.Nickname
+//	nicknameOpt := optional.MakeOptional(
+//	    func(p Person) option.Option[string] {
+//	        if p.Nickname != nil {
+//	            return option.Some(*p.Nickname)
+//	        }
+//	        return option.None[string]()
+//	    },
+//	    func(p Person, nick string) Person {
+//	        p.Nickname = &nick
+//	        return p
+//	    },
+//	)
+//
+//	// Build a Person codec with optional nickname
+//	personCodec := F.Pipe1(
+//	    codec.Struct[Person]("Person"),
+//	    codec.ApSO(S.Monoid, nicknameOpt, codec.String),
+//	)
+//
+//	// Encoding with nickname present
+//	p1 := Person{Name: "Alice", Nickname: ptr("Ali")}
+//	encoded1 := personCodec.Encode(p1)  // Includes nickname
+//
+//	// Encoding with nickname absent
+//	p2 := Person{Name: "Bob", Nickname: nil}
+//	encoded2 := personCodec.Encode(p2)  // No nickname in output
+//
+// # Use Cases
+//
+//   - Building struct codecs with optional/nullable fields
+//   - Handling pointer fields that may be nil
+//   - Composing codecs for structures with optional nested data
+//   - Creating flexible serialization that omits absent fields
+//
+// # Notes
+//
+//   - The monoid determines how encoded outputs are combined when field is present
+//   - When the optional field is absent, encoding returns base encoding unchanged
+//   - Validation still accumulates errors even for optional fields
+//   - The name is automatically generated for debugging purposes
+//
+// # See Also
+//
+//   - ApSL: For required fields using Lens
+//   - validate.ApS: The underlying validation combinator
+//   - Optional: The optic for accessing optional fields
+func ApSO[S, T, O, I any](
+	m Monoid[O],
+	o Optional[S, T],
+	fa Type[T, O, I],
+) Operator[S, S, O, I] {
+	name := fmt.Sprintf("ApS[%s x %s]", o, fa)
+
+	encConcat := F.Flow2(
+		o.GetOption,
+		option.Map(F.Flow2(
+			fa.Encode,
+			semigroup.AppendTo(m),
+		)),
+	)
+
+	valConcat := validate.ApS(o.Set, fa.Validate)
+
+	return func(t Type[S, O, I]) Type[S, O, I] {
+
+		return MakeType(
+			name,
+			t.Is,
+			F.Pipe1(
+				t.Validate,
+				valConcat,
+			),
+			func(s S) O {
+				to := t.Encode(s)
+				return F.Pipe2(
+					encConcat(s),
+					option.Flap[O](to),
+					option.GetOrElse(lazy.Of(to)),
+				)
+			},
+		)
+	}
+}

v2/optics/codec/bind_test.go

@@ -0,0 +1,818 @@
+// Copyright (c) 2023 - 2025 IBM Corp.
+// All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package codec
+
+import (
+	"strconv"
+	"testing"
+
+	"github.com/IBM/fp-go/v2/either"
+	F "github.com/IBM/fp-go/v2/function"
+	"github.com/IBM/fp-go/v2/optics/codec/validation"
+	"github.com/IBM/fp-go/v2/optics/lens"
+	"github.com/IBM/fp-go/v2/optics/optional"
+	"github.com/IBM/fp-go/v2/option"
+	S "github.com/IBM/fp-go/v2/string"
+	"github.com/stretchr/testify/assert"
+)
+
+// Test types for ApSL
+type Person struct {
+	Name string
+	Age  int
+}
+
+func TestApSL_EncodingCombination(t *testing.T) {
+	t.Run("combines encodings using monoid", func(t *testing.T) {
+		// Create a lens for Person.Name
+		nameLens := lens.MakeLens(
+			func(p Person) string { return p.Name },
+			func(p Person, name string) Person {
+				return Person{Name: name, Age: p.Age}
+			},
+		)
+
+		// Create base codec that encodes to "Person:"
+		baseCodec := MakeType(
+			"Person",
+			func(i any) validation.Result[Person] {
+				if p, ok := i.(Person); ok {
+					return validation.ToResult(validation.Success(p))
+				}
+				return validation.ToResult(validation.Failures[Person](validation.Errors{
+					&validation.ValidationError{
+						Value:    i,
+						Messsage: "expected Person",
+					},
+				}))
+			},
+			func(i any) Decode[Context, Person] {
+				return func(ctx Context) validation.Validation[Person] {
+					if p, ok := i.(Person); ok {
+						return validation.Success(p)
+					}
+					return validation.FailureWithMessage[Person](i, "expected Person")(ctx)
+				}
+			},
+			func(p Person) string { return "Person:" },
+		)
+
+		// Create field codec for Name
+		nameCodec := MakeType(
+			"Name",
+			func(i any) validation.Result[string] {
+				if s, ok := i.(string); ok {
+					return validation.ToResult(validation.Success(s))
+				}
+				return validation.ToResult(validation.Failures[string](validation.Errors{
+					&validation.ValidationError{
+						Value:    i,
+						Messsage: "expected string",
+					},
+				}))
+			},
+			func(i any) Decode[Context, string] {
+				return func(ctx Context) validation.Validation[string] {
+					if s, ok := i.(string); ok {
+						return validation.Success(s)
+					}
+					return validation.FailureWithMessage[string](i, "expected string")(ctx)
+				}
+			},
+			F.Identity[string],
+		)
+
+		// Apply ApSL to combine encodings
+		operator := ApSL(S.Monoid, nameLens, nameCodec)
+		enhancedCodec := operator(baseCodec)
+
+		// Test encoding - should concatenate base encoding with field encoding
+		person := Person{Name: "Alice", Age: 30}
+		encoded := enhancedCodec.Encode(person)
+
+		// The monoid concatenates: base encoding + field encoding
+		// Note: The order depends on how the monoid is applied in ApSL
+		assert.Contains(t, encoded, "Person:")
+		assert.Contains(t, encoded, "Alice")
+	})
+}
+
+func TestApSL_ValidationCombination(t *testing.T) {
+	t.Run("validates field through lens", func(t *testing.T) {
+		// Create a lens for Person.Age
+		ageLens := lens.MakeLens(
+			func(p Person) int { return p.Age },
+			func(p Person, age int) Person {
+				return Person{Name: p.Name, Age: age}
+			},
+		)
+
+		// Create base codec that always succeeds
+		baseCodec := MakeType(
+			"Person",
+			func(i any) validation.Result[Person] {
+				if p, ok := i.(Person); ok {
+					return validation.ToResult(validation.Success(p))
+				}
+				return validation.ToResult(validation.Failures[Person](validation.Errors{
+					&validation.ValidationError{
+						Value:    i,
+						Messsage: "expected Person",
+					},
+				}))
+			},
+			func(i any) Decode[Context, Person] {
+				return func(ctx Context) validation.Validation[Person] {
+					if p, ok := i.(Person); ok {
+						return validation.Success(p)
+					}
+					return validation.FailureWithMessage[Person](i, "expected Person")(ctx)
+				}
+			},
+			func(p Person) string { return "" },
+		)
+
+		// Create field codec for Age that validates positive numbers
+		ageCodec := MakeType(
+			"Age",
+			func(i any) validation.Result[int] {
+				if n, ok := i.(int); ok {
+					if n > 0 {
+						return validation.ToResult(validation.Success(n))
+					}
+					return validation.ToResult(validation.Failures[int](validation.Errors{
+						&validation.ValidationError{
+							Value:    n,
+							Messsage: "age must be positive",
+						},
+					}))
+				}
+				return validation.ToResult(validation.Failures[int](validation.Errors{
+					&validation.ValidationError{
+						Value:    i,
+						Messsage: "expected int",
+					},
+				}))
+			},
+			func(i any) Decode[Context, int] {
+				return func(ctx Context) validation.Validation[int] {
+					if n, ok := i.(int); ok {
+						if n > 0 {
+							return validation.Success(n)
+						}
+						return validation.FailureWithMessage[int](n, "age must be positive")(ctx)
+					}
+					return validation.FailureWithMessage[int](i, "expected int")(ctx)
+				}
+			},
+			strconv.Itoa,
+		)
+
+		// Apply ApSL
+		operator := ApSL(S.Monoid, ageLens, ageCodec)
+		enhancedCodec := operator(baseCodec)
+
+		// Test with invalid age (negative) - field validation should fail
+		invalidPerson := Person{Name: "Charlie", Age: -5}
+		invalidResult := enhancedCodec.Decode(invalidPerson)
+		assert.True(t, either.IsLeft(invalidResult), "Should fail with negative age")
+
+		// Extract and verify we have errors
+		errors := either.MonadFold(invalidResult,
+			F.Identity[validation.Errors],
+			func(Person) validation.Errors { return nil },
+		)
+		assert.NotEmpty(t, errors, "Should have validation errors")
+	})
+}
+
+func TestApSL_TypeChecking(t *testing.T) {
+	t.Run("preserves base type checker", func(t *testing.T) {
+		// Create a lens for Person.Name
+		nameLens := lens.MakeLens(
+			func(p Person) string { return p.Name },
+			func(p Person, name string) Person {
+				return Person{Name: name, Age: p.Age}
+			},
+		)
+
+		// Create base codec with type checker
+		baseCodec := MakeType(
+			"Person",
+			func(i any) validation.Result[Person] {
+				if p, ok := i.(Person); ok {
+					return validation.ToResult(validation.Success(p))
+				}
+				return validation.ToResult(validation.Failures[Person](validation.Errors{
+					&validation.ValidationError{
+						Value:    i,
+						Messsage: "expected Person",
+					},
+				}))
+			},
+			func(i any) Decode[Context, Person] {
+				return func(ctx Context) validation.Validation[Person] {
+					if p, ok := i.(Person); ok {
+						return validation.Success(p)
+					}
+					return validation.FailureWithMessage[Person](i, "expected Person")(ctx)
+				}
+			},
+			func(p Person) string { return "" },
+		)
+
+		// Create field codec
+		nameCodec := MakeType(
+			"Name",
+			func(i any) validation.Result[string] {
+				if s, ok := i.(string); ok {
+					return validation.ToResult(validation.Success(s))
+				}
+				return validation.ToResult(validation.Failures[string](validation.Errors{
+					&validation.ValidationError{
+						Value:    i,
+						Messsage: "expected string",
+					},
+				}))
+			},
+			func(i any) Decode[Context, string] {
+				return func(ctx Context) validation.Validation[string] {
+					if s, ok := i.(string); ok {
+						return validation.Success(s)
+					}
+					return validation.FailureWithMessage[string](i, "expected string")(ctx)
+				}
+			},
+			F.Identity[string],
+		)
+
+		// Apply ApSL
+		operator := ApSL(S.Monoid, nameLens, nameCodec)
+		enhancedCodec := operator(baseCodec)
+
+		// Test type checking with valid type
+		person := Person{Name: "Eve", Age: 22}
+		isResult := enhancedCodec.Is(person)
+		assert.True(t, either.IsRight(isResult), "Should accept Person type")
+
+		// Test type checking with invalid type
+		invalidResult := enhancedCodec.Is("not a person")
+		assert.True(t, either.IsLeft(invalidResult), "Should reject non-Person type")
+	})
+}
+
+func TestApSL_Naming(t *testing.T) {
+	t.Run("generates descriptive name", func(t *testing.T) {
+		// Create a lens for Person.Name
+		nameLens := lens.MakeLens(
+			func(p Person) string { return p.Name },
+			func(p Person, name string) Person {
+				return Person{Name: name, Age: p.Age}
+			},
+		)
+
+		// Create base codec
+		baseCodec := MakeType(
+			"Person",
+			func(i any) validation.Result[Person] {
+				if p, ok := i.(Person); ok {
+					return validation.ToResult(validation.Success(p))
+				}
+				return validation.ToResult(validation.Failures[Person](validation.Errors{
+					&validation.ValidationError{
+						Value:    i,
+						Messsage: "expected Person",
+					},
+				}))
+			},
+			func(i any) Decode[Context, Person] {
+				return func(ctx Context) validation.Validation[Person] {
+					if p, ok := i.(Person); ok {
+						return validation.Success(p)
+					}
+					return validation.FailureWithMessage[Person](i, "expected Person")(ctx)
+				}
+			},
+			func(p Person) string { return "" },
+		)
+
+		// Create field codec
+		nameCodec := MakeType(
+			"Name",
+			func(i any) validation.Result[string] {
+				if s, ok := i.(string); ok {
+					return validation.ToResult(validation.Success(s))
+				}
+				return validation.ToResult(validation.Failures[string](validation.Errors{
+					&validation.ValidationError{
+						Value:    i,
+						Messsage: "expected string",
+					},
+				}))
+			},
+			func(i any) Decode[Context, string] {
+				return func(ctx Context) validation.Validation[string] {
+					if s, ok := i.(string); ok {
+						return validation.Success(s)
+					}
+					return validation.FailureWithMessage[string](i, "expected string")(ctx)
+				}
+			},
+			F.Identity[string],
+		)
+
+		// Apply ApSL
+		operator := ApSL(S.Monoid, nameLens, nameCodec)
+		enhancedCodec := operator(baseCodec)
+
+		// Check that the name includes ApS
+		name := enhancedCodec.Name()
+		assert.Contains(t, name, "ApS", "Name should contain 'ApS'")
+	})
+}
+
+func TestApSL_ErrorAccumulation(t *testing.T) {
+	t.Run("accumulates validation errors", func(t *testing.T) {
+		// Create a lens for Person.Age
+		ageLens := lens.MakeLens(
+			func(p Person) int { return p.Age },
+			func(p Person, age int) Person {
+				return Person{Name: p.Name, Age: age}
+			},
+		)
+
+		// Create base codec that fails validation
+		baseCodec := MakeType(
+			"Person",
+			func(i any) validation.Result[Person] {
+				return validation.ToResult(validation.Failures[Person](validation.Errors{
+					&validation.ValidationError{
+						Value:    i,
+						Messsage: "base validation error",
+					},
+				}))
+			},
+			func(i any) Decode[Context, Person] {
+				return func(ctx Context) validation.Validation[Person] {
+					return validation.FailureWithMessage[Person](i, "base validation error")(ctx)
+				}
+			},
+			func(p Person) string { return "" },
+		)
+
+		// Create field codec that also fails
+		ageCodec := MakeType(
+			"Age",
+			func(i any) validation.Result[int] {
+				return validation.ToResult(validation.Failures[int](validation.Errors{
+					&validation.ValidationError{
+						Value:    i,
+						Messsage: "age validation error",
+					},
+				}))
+			},
+			func(i any) Decode[Context, int] {
+				return func(ctx Context) validation.Validation[int] {
+					return validation.FailureWithMessage[int](i, "age validation error")(ctx)
+				}
+			},
+			strconv.Itoa,
+		)
+
+		// Apply ApSL
+		operator := ApSL(S.Monoid, ageLens, ageCodec)
+		enhancedCodec := operator(baseCodec)
+
+		// Test validation - should accumulate errors
+		person := Person{Name: "Dave", Age: 30}
+		result := enhancedCodec.Decode(person)
+
+		// Should fail
+		assert.True(t, either.IsLeft(result), "Should fail validation")
+
+		// Extract errors
+		errors := either.MonadFold(result,
+			F.Identity[validation.Errors],
+			func(Person) validation.Errors { return nil },
+		)
+
+		// Should have errors from both base and field validation
+		assert.NotEmpty(t, errors, "Should have validation errors")
+	})
+}
+
+// Test types for ApSO
+type PersonWithNickname struct {
+	Name     string
+	Nickname *string
+}
+
+func TestApSO_EncodingWithPresentField(t *testing.T) {
+	t.Run("encodes optional field when present", func(t *testing.T) {
+		// Create an optional for PersonWithNickname.Nickname
+		nicknameOpt := optional.MakeOptional(
+			func(p PersonWithNickname) option.Option[string] {
+				if p.Nickname != nil {
+					return option.Some(*p.Nickname)
+				}
+				return option.None[string]()
+			},
+			func(p PersonWithNickname, nick string) PersonWithNickname {
+				p.Nickname = &nick
+				return p
+			},
+		)
+
+		// Create base codec that encodes to "Person:"
+		baseCodec := MakeType(
+			"PersonWithNickname",
+			func(i any) validation.Result[PersonWithNickname] {
+				if p, ok := i.(PersonWithNickname); ok {
+					return validation.ToResult(validation.Success(p))
+				}
+				return validation.ToResult(validation.Failures[PersonWithNickname](validation.Errors{
+					&validation.ValidationError{
+						Value:    i,
+						Messsage: "expected PersonWithNickname",
+					},
+				}))
+			},
+			func(i any) Decode[Context, PersonWithNickname] {
+				return func(ctx Context) validation.Validation[PersonWithNickname] {
+					if p, ok := i.(PersonWithNickname); ok {
+						return validation.Success(p)
+					}
+					return validation.FailureWithMessage[PersonWithNickname](i, "expected PersonWithNickname")(ctx)
+				}
+			},
+			func(p PersonWithNickname) string { return "Person:" },
+		)
+
+		// Create field codec for Nickname
+		nicknameCodec := MakeType(
+			"Nickname",
+			func(i any) validation.Result[string] {
+				if s, ok := i.(string); ok {
+					return validation.ToResult(validation.Success(s))
+				}
+				return validation.ToResult(validation.Failures[string](validation.Errors{
+					&validation.ValidationError{
+						Value:    i,
+						Messsage: "expected string",
+					},
+				}))
+			},
+			func(i any) Decode[Context, string] {
+				return func(ctx Context) validation.Validation[string] {
+					if s, ok := i.(string); ok {
+						return validation.Success(s)
+					}
+					return validation.FailureWithMessage[string](i, "expected string")(ctx)
+				}
+			},
+			F.Identity[string],
+		)
+
+		// Apply ApSO to combine encodings
+		operator := ApSO(S.Monoid, nicknameOpt, nicknameCodec)
+		enhancedCodec := operator(baseCodec)
+
+		// Test encoding with nickname present
+		nickname := "Ali"
+		person := PersonWithNickname{Name: "Alice", Nickname: &nickname}
+		encoded := enhancedCodec.Encode(person)
+
+		// Should include both base and nickname
+		assert.Contains(t, encoded, "Person:")
+		assert.Contains(t, encoded, "Ali")
+	})
+}
+
+func TestApSO_EncodingWithAbsentField(t *testing.T) {
+	t.Run("omits optional field when absent", func(t *testing.T) {
+		// Create an optional for PersonWithNickname.Nickname
+		nicknameOpt := optional.MakeOptional(
+			func(p PersonWithNickname) option.Option[string] {
+				if p.Nickname != nil {
+					return option.Some(*p.Nickname)
+				}
+				return option.None[string]()
+			},
+			func(p PersonWithNickname, nick string) PersonWithNickname {
+				p.Nickname = &nick
+				return p
+			},
+		)
+
+		// Create base codec
+		baseCodec := MakeType(
+			"PersonWithNickname",
+			func(i any) validation.Result[PersonWithNickname] {
+				if p, ok := i.(PersonWithNickname); ok {
+					return validation.ToResult(validation.Success(p))
+				}
+				return validation.ToResult(validation.Failures[PersonWithNickname](validation.Errors{
+					&validation.ValidationError{
+						Value:    i,
+						Messsage: "expected PersonWithNickname",
+					},
+				}))
+			},
+			func(i any) Decode[Context, PersonWithNickname] {
+				return func(ctx Context) validation.Validation[PersonWithNickname] {
+					if p, ok := i.(PersonWithNickname); ok {
+						return validation.Success(p)
+					}
+					return validation.FailureWithMessage[PersonWithNickname](i, "expected PersonWithNickname")(ctx)
+				}
+			},
+			func(p PersonWithNickname) string { return "Person:Bob" },
+		)
+
+		// Create field codec
+		nicknameCodec := MakeType(
+			"Nickname",
+			func(i any) validation.Result[string] {
+				if s, ok := i.(string); ok {
+					return validation.ToResult(validation.Success(s))
+				}
+				return validation.ToResult(validation.Failures[string](validation.Errors{
+					&validation.ValidationError{
+						Value:    i,
+						Messsage: "expected string",
+					},
+				}))
+			},
+			func(i any) Decode[Context, string] {
+				return func(ctx Context) validation.Validation[string] {
+					if s, ok := i.(string); ok {
+						return validation.Success(s)
+					}
+					return validation.FailureWithMessage[string](i, "expected string")(ctx)
+				}
+			},
+			F.Identity[string],
+		)
+
+		// Apply ApSO
+		operator := ApSO(S.Monoid, nicknameOpt, nicknameCodec)
+		enhancedCodec := operator(baseCodec)
+
+		// Test encoding with nickname absent
+		person := PersonWithNickname{Name: "Bob", Nickname: nil}
+		encoded := enhancedCodec.Encode(person)
+
+		// Should only have base encoding
+		assert.Equal(t, "Person:Bob", encoded)
+	})
+}
+
+func TestApSO_TypeChecking(t *testing.T) {
+	t.Run("preserves base type checker", func(t *testing.T) {
+		// Create an optional for PersonWithNickname.Nickname
+		nicknameOpt := optional.MakeOptional(
+			func(p PersonWithNickname) option.Option[string] {
+				if p.Nickname != nil {
+					return option.Some(*p.Nickname)
+				}
+				return option.None[string]()
+			},
+			func(p PersonWithNickname, nick string) PersonWithNickname {
+				p.Nickname = &nick
+				return p
+			},
+		)
+
+		// Create base codec with type checker
+		baseCodec := MakeType(
+			"PersonWithNickname",
+			func(i any) validation.Result[PersonWithNickname] {
+				if p, ok := i.(PersonWithNickname); ok {
+					return validation.ToResult(validation.Success(p))
+				}
+				return validation.ToResult(validation.Failures[PersonWithNickname](validation.Errors{
+					&validation.ValidationError{
+						Value:    i,
+						Messsage: "expected PersonWithNickname",
+					},
+				}))
+			},
+			func(i any) Decode[Context, PersonWithNickname] {
+				return func(ctx Context) validation.Validation[PersonWithNickname] {
+					if p, ok := i.(PersonWithNickname); ok {
+						return validation.Success(p)
+					}
+					return validation.FailureWithMessage[PersonWithNickname](i, "expected PersonWithNickname")(ctx)
+				}
+			},
+			func(p PersonWithNickname) string { return "" },
+		)
+
+		// Create field codec
+		nicknameCodec := MakeType(
+			"Nickname",
+			func(i any) validation.Result[string] {
+				if s, ok := i.(string); ok {
+					return validation.ToResult(validation.Success(s))
+				}
+				return validation.ToResult(validation.Failures[string](validation.Errors{
+					&validation.ValidationError{
+						Value:    i,
+						Messsage: "expected string",
+					},
+				}))
+			},
+			func(i any) Decode[Context, string] {
+				return func(ctx Context) validation.Validation[string] {
+					if s, ok := i.(string); ok {
+						return validation.Success(s)
+					}
+					return validation.FailureWithMessage[string](i, "expected string")(ctx)
+				}
+			},
+			F.Identity[string],
+		)
+
+		// Apply ApSO
+		operator := ApSO(S.Monoid, nicknameOpt, nicknameCodec)
+		enhancedCodec := operator(baseCodec)
+
+		// Test type checking with valid type
+		nickname := "Eve"
+		person := PersonWithNickname{Name: "Eve", Nickname: &nickname}
+		isResult := enhancedCodec.Is(person)
+		assert.True(t, either.IsRight(isResult), "Should accept PersonWithNickname type")
+
+		// Test type checking with invalid type
+		invalidResult := enhancedCodec.Is("not a person")
+		assert.True(t, either.IsLeft(invalidResult), "Should reject non-PersonWithNickname type")
+	})
+}
+
+func TestApSO_Naming(t *testing.T) {
+	t.Run("generates descriptive name", func(t *testing.T) {
+		// Create an optional for PersonWithNickname.Nickname
+		nicknameOpt := optional.MakeOptional(
+			func(p PersonWithNickname) option.Option[string] {
+				if p.Nickname != nil {
+					return option.Some(*p.Nickname)
+				}
+				return option.None[string]()
+			},
+			func(p PersonWithNickname, nick string) PersonWithNickname {
+				p.Nickname = &nick
+				return p
+			},
+		)
+
+		// Create base codec
+		baseCodec := MakeType(
+			"PersonWithNickname",
+			func(i any) validation.Result[PersonWithNickname] {
+				if p, ok := i.(PersonWithNickname); ok {
+					return validation.ToResult(validation.Success(p))
+				}
+				return validation.ToResult(validation.Failures[PersonWithNickname](validation.Errors{
+					&validation.ValidationError{
+						Value:    i,
+						Messsage: "expected PersonWithNickname",
+					},
+				}))
+			},
+			func(i any) Decode[Context, PersonWithNickname] {
+				return func(ctx Context) validation.Validation[PersonWithNickname] {
+					if p, ok := i.(PersonWithNickname); ok {
+						return validation.Success(p)
+					}
+					return validation.FailureWithMessage[PersonWithNickname](i, "expected PersonWithNickname")(ctx)
+				}
+			},
+			func(p PersonWithNickname) string { return "" },
+		)
+
+		// Create field codec
+		nicknameCodec := MakeType(
+			"Nickname",
+			func(i any) validation.Result[string] {
+				if s, ok := i.(string); ok {
+					return validation.ToResult(validation.Success(s))
+				}
+				return validation.ToResult(validation.Failures[string](validation.Errors{
+					&validation.ValidationError{
+						Value:    i,
+						Messsage: "expected string",
+					},
+				}))
+			},
+			func(i any) Decode[Context, string] {
+				return func(ctx Context) validation.Validation[string] {
+					if s, ok := i.(string); ok {
+						return validation.Success(s)
+					}
+					return validation.FailureWithMessage[string](i, "expected string")(ctx)
+				}
+			},
+			F.Identity[string],
+		)
+
+		// Apply ApSO
+		operator := ApSO(S.Monoid, nicknameOpt, nicknameCodec)
+		enhancedCodec := operator(baseCodec)
+
+		// Check that the name includes ApS
+		name := enhancedCodec.Name()
+		assert.Contains(t, name, "ApS", "Name should contain 'ApS'")
+	})
+}
+
+func TestApSO_ErrorAccumulation(t *testing.T) {
+	t.Run("accumulates validation errors", func(t *testing.T) {
+		// Create an optional for PersonWithNickname.Nickname
+		nicknameOpt := optional.MakeOptional(
+			func(p PersonWithNickname) option.Option[string] {
+				if p.Nickname != nil {
+					return option.Some(*p.Nickname)
+				}
+				return option.None[string]()
+			},
+			func(p PersonWithNickname, nick string) PersonWithNickname {
+				p.Nickname = &nick
+				return p
+			},
+		)
+
+		// Create base codec that fails validation
+		baseCodec := MakeType(
+			"PersonWithNickname",
+			func(i any) validation.Result[PersonWithNickname] {
+				return validation.ToResult(validation.Failures[PersonWithNickname](validation.Errors{
+					&validation.ValidationError{
+						Value:    i,
+						Messsage: "base validation error",
+					},
+				}))
+			},
+			func(i any) Decode[Context, PersonWithNickname] {
+				return func(ctx Context) validation.Validation[PersonWithNickname] {
+					return validation.FailureWithMessage[PersonWithNickname](i, "base validation error")(ctx)
+				}
+			},
+			func(p PersonWithNickname) string { return "" },
+		)
+
+		// Create field codec that also fails
+		nicknameCodec := MakeType(
+			"Nickname",
+			func(i any) validation.Result[string] {
+				return validation.ToResult(validation.Failures[string](validation.Errors{
+					&validation.ValidationError{
+						Value:    i,
+						Messsage: "nickname validation error",
+					},
+				}))
+			},
+			func(i any) Decode[Context, string] {
+				return func(ctx Context) validation.Validation[string] {
+					return validation.FailureWithMessage[string](i, "nickname validation error")(ctx)
+				}
+			},
+			F.Identity[string],
+		)
+
+		// Apply ApSO
+		operator := ApSO(S.Monoid, nicknameOpt, nicknameCodec)
+		enhancedCodec := operator(baseCodec)
+
+		// Test validation with present nickname - should accumulate errors
+		nickname := "Dave"
+		person := PersonWithNickname{Name: "Dave", Nickname: &nickname}
+		result := enhancedCodec.Decode(person)
+
+		// Should fail
+		assert.True(t, either.IsLeft(result), "Should fail validation")
+
+		// Extract errors
+		errors := either.MonadFold(result,
+			F.Identity[validation.Errors],
+			func(PersonWithNickname) validation.Errors { return nil },
+		)
+
+		// Should have errors from both base and field validation
+		assert.NotEmpty(t, errors, "Should have validation errors")
+	})
+}
+
+// Made with Bob

v2/optics/codec/codec.go

@@ -100,7 +100,7 @@ func (t *typeImpl[A, O, I]) Is(i any) Result[A] {
 //	stringToInt := codec.MakeType(...)  // Type[int, string, string]
 //	intToPositive := codec.MakeType(...) // Type[PositiveInt, int, int]
 //	composed := codec.Pipe(intToPositive)(stringToInt) // Type[PositiveInt, string, string]
-func Pipe[A, B, O, I any](ab Type[B, A, A]) func(Type[A, O, I]) Type[B, O, I] {
+func Pipe[O, I, A, B any](ab Type[B, A, A]) func(Type[A, O, I]) Type[B, O, I] {
 	return func(this Type[A, O, I]) Type[B, O, I] {
 		return MakeType(
 			fmt.Sprintf("Pipe(%s, %s)", this.Name(), ab.Name()),

v2/optics/codec/codec_test.go

@@ -1748,7 +1748,7 @@ func TestFromRefinementComposition(t *testing.T) {
 	positiveCodec := FromRefinement(positiveIntPrism)
 
 	// Compose with Int codec using Pipe
-	composed := Pipe[int, int, int, any](positiveCodec)(Int())
+	composed := Pipe[int, any, int, int](positiveCodec)(Int())
 
 	t.Run("ComposedDecodeValid", func(t *testing.T) {
 		result := composed.Decode(42)

v2/optics/codec/codecs_test.go

@@ -159,7 +159,7 @@ func TestURL(t *testing.T) {
 
 func TestDate(t *testing.T) {
 
-	getOrElseNull := either.GetOrElse(reader.Of[validation.Errors, time.Time](time.Time{}))
+	getOrElseNull := either.GetOrElse(reader.Of[validation.Errors](time.Time{}))
 
 	t.Run("ISO 8601 date format", func(t *testing.T) {
 		dateCodec := Date("2006-01-02")

v2/optics/codec/either_test.go

@@ -70,7 +70,7 @@ func TestEitherEncode(t *testing.T) {
 
 // TestEitherDecode tests decoding/validation of Either values
 func TestEitherDecode(t *testing.T) {
-	getOrElseNull := either.GetOrElse(reader.Of[validation.Errors, either.Either[string, int]](either.Left[int]("")))
+	getOrElseNull := either.GetOrElse(reader.Of[validation.Errors](either.Left[int]("")))
 
 	// Create codecs that both work with string input
 	stringCodec := Id[string]()

v2/optics/codec/types.go

@@ -10,6 +10,8 @@ import (
 	"github.com/IBM/fp-go/v2/optics/codec/validation"
 	"github.com/IBM/fp-go/v2/optics/decoder"
 	"github.com/IBM/fp-go/v2/optics/encoder"
+	"github.com/IBM/fp-go/v2/optics/lens"
+	"github.com/IBM/fp-go/v2/optics/optional"
 	"github.com/IBM/fp-go/v2/optics/prism"
 	"github.com/IBM/fp-go/v2/option"
 	"github.com/IBM/fp-go/v2/pair"
@@ -338,4 +340,104 @@ type (
 	//   - ApplicativeMonoid: Combines successful results using inner monoid
 	//   - AlternativeMonoid: Combines applicative and alternative behaviors
 	Monoid[A any] = monoid.Monoid[A]
+
+	// Lens is an optic that focuses on a specific field within a product type S.
+	// It provides a way to get and set a field of type A within a structure of type S.
+	//
+	// A Lens[S, A] represents a relationship between a source type S and a focus type A,
+	// where the focus always exists (unlike Optional which may not exist).
+	//
+	// Lens operations:
+	//   - Get: Extract the field value A from structure S
+	//   - Set: Update the field value A in structure S, returning a new S
+	//
+	// Lens laws:
+	//   1. GetSet: If you get a value and then set it back, nothing changes
+	//      Set(Get(s))(s) = s
+	//   2. SetGet: If you set a value, you can get it back
+	//      Get(Set(a)(s)) = a
+	//   3. SetSet: Setting twice is the same as setting once with the final value
+	//      Set(b)(Set(a)(s)) = Set(b)(s)
+	//
+	// In the codec context, lenses are used with ApSL to build codecs for struct fields:
+	//   - Extract field values for encoding
+	//   - Update field values during validation
+	//   - Compose codec operations on nested structures
+	//
+	// Example:
+	//   type Person struct { Name string; Age int }
+	//
+	//   nameLens := lens.MakeLens(
+	//       func(p Person) string { return p.Name },
+	//       func(p Person, name string) Person { p.Name = name; return p },
+	//   )
+	//
+	//   // Use with ApSL to build a codec
+	//   personCodec := F.Pipe1(
+	//       codec.Struct[Person]("Person"),
+	//       codec.ApSL(S.Monoid, nameLens, codec.String),
+	//   )
+	//
+	// See also:
+	//   - ApSL: Applicative sequencing with lens
+	//   - Optional: For fields that may not exist
+	Lens[S, A any] = lens.Lens[S, A]
+
+	// Optional is an optic that focuses on a field within a product type S that may not exist.
+	// It provides a way to get and set an optional field of type A within a structure of type S.
+	//
+	// An Optional[S, A] represents a relationship between a source type S and a focus type A,
+	// where the focus may or may not be present (unlike Lens where it always exists).
+	//
+	// Optional operations:
+	//   - GetOption: Try to extract the field value, returning Option[A]
+	//   - Set: Update the field value if it exists, returning a new S
+	//
+	// Optional laws:
+	//   1. GetSet (No-op on None): If GetOption returns None, Set has no effect
+	//      GetOption(s) = None => Set(a)(s) = s
+	//   2. SetGet (Get what you Set): If GetOption returns Some, you can get back what you set
+	//      GetOption(s) = Some(_) => GetOption(Set(a)(s)) = Some(a)
+	//   3. SetSet (Last Set Wins): Setting twice is the same as setting once with the final value
+	//      Set(b)(Set(a)(s)) = Set(b)(s)
+	//
+	// In the codec context, optionals are used with ApSO to build codecs for optional fields:
+	//   - Extract optional field values for encoding (only if present)
+	//   - Update optional field values during validation
+	//   - Handle nullable or pointer fields gracefully
+	//   - Compose codec operations on structures with optional data
+	//
+	// Example:
+	//   type Person struct {
+	//       Name     string
+	//       Nickname *string  // Optional field
+	//   }
+	//
+	//   nicknameOpt := optional.MakeOptional(
+	//       func(p Person) option.Option[string] {
+	//           if p.Nickname != nil {
+	//               return option.Some(*p.Nickname)
+	//           }
+	//           return option.None[string]()
+	//       },
+	//       func(p Person, nick string) Person {
+	//           p.Nickname = &nick
+	//           return p
+	//       },
+	//   )
+	//
+	//   // Use with ApSO to build a codec with optional field
+	//   personCodec := F.Pipe1(
+	//       codec.Struct[Person]("Person"),
+	//       codec.ApSO(S.Monoid, nicknameOpt, codec.String),
+	//   )
+	//
+	//   // Encoding omits the field when absent
+	//   p1 := Person{Name: "Alice", Nickname: nil}
+	//   encoded := personCodec.Encode(p1)  // No nickname in output
+	//
+	// See also:
+	//   - ApSO: Applicative sequencing with optional
+	//   - Lens: For fields that always exist
+	Optional[S, A any] = optional.Optional[S, A]
 )

v2/optics/codec/validate/from_test.go

@@ -39,7 +39,7 @@ func TestFromReaderResult_Success(t *testing.T) {
 		}
 
 		// Convert to Validate
-		validator := FromReaderResult[int, string](successRR)
+		validator := FromReaderResult(successRR)
 
 		// Execute the validator
 		validationResult := validator(42)(nil)
@@ -53,7 +53,7 @@ func TestFromReaderResult_Success(t *testing.T) {
 		parseIntRR := result.Eitherize1(strconv.Atoi)
 
 		// Convert to Validate
-		validator := FromReaderResult[string, int](parseIntRR)
+		validator := FromReaderResult(parseIntRR)
 
 		// Execute with valid input
 		validationResult := validator("123")(nil)
@@ -74,7 +74,7 @@ func TestFromReaderResult_Success(t *testing.T) {
 		}
 
 		// Convert to Validate
-		validator := FromReaderResult[string, User](createUserRR)
+		validator := FromReaderResult(createUserRR)
 
 		// Execute the validator
 		validationResult := validator("Alice")(nil)
@@ -88,7 +88,7 @@ func TestFromReaderResult_Success(t *testing.T) {
 			return result.Of(input * 2)
 		}
 
-		validator := FromReaderResult[int, int](successRR)
+		validator := FromReaderResult(successRR)
 		validationResult := validator(21)(Context{})
 
 		assert.Equal(t, validation.Success(42), validationResult)
@@ -99,7 +99,7 @@ func TestFromReaderResult_Success(t *testing.T) {
 			return result.Of(input + " processed")
 		}
 
-		validator := FromReaderResult[string, string](successRR)
+		validator := FromReaderResult(successRR)
 		ctx := Context{
 			{Key: "user", Type: "User"},
 			{Key: "name", Type: "string"},
@@ -122,7 +122,7 @@ func TestFromReaderResult_Failure(t *testing.T) {
 		}
 
 		// Convert to Validate
-		validator := FromReaderResult[string, int](failureRR)
+		validator := FromReaderResult(failureRR)
 
 		// Execute the validator
 		validationResult := validator("invalid")(nil)
@@ -147,7 +147,7 @@ func TestFromReaderResult_Failure(t *testing.T) {
 			return result.Left[string](originalErr)
 		}
 
-		validator := FromReaderResult[int, string](failureRR)
+		validator := FromReaderResult(failureRR)
 		validationResult := validator(42)(nil)
 
 		assert.True(t, either.IsLeft(validationResult))
@@ -166,7 +166,7 @@ func TestFromReaderResult_Failure(t *testing.T) {
 			return result.Left[int](errors.New("conversion failed"))
 		}
 
-		validator := FromReaderResult[string, int](failureRR)
+		validator := FromReaderResult(failureRR)
 		ctx := Context{
 			{Key: "user", Type: "User"},
 			{Key: "age", Type: "int"},
@@ -213,7 +213,7 @@ func TestFromReaderResult_Failure(t *testing.T) {
 					return result.Left[int](tc.err)
 				}
 
-				validator := FromReaderResult[string, int](failureRR)
+				validator := FromReaderResult(failureRR)
 				validationResult := validator(tc.input)(nil)
 
 				assert.True(t, either.IsLeft(validationResult))
@@ -251,7 +251,7 @@ func TestFromReaderResult_Integration(t *testing.T) {
 
 		// Combine validators
 		validator := F.Pipe1(
-			FromReaderResult[string, int](parseIntRR),
+			FromReaderResult(parseIntRR),
 			Chain(validatePositive),
 		)
 
@@ -273,8 +273,8 @@ func TestFromReaderResult_Integration(t *testing.T) {
 
 		// Convert and map to double the value
 		validator := F.Pipe1(
-			FromReaderResult[string, int](parseIntRR),
-			Map[string, int, int](func(n int) int { return n * 2 }),
+			FromReaderResult(parseIntRR),
+			Map[string](func(n int) int { return n * 2 }),
 		)
 
 		validationResult := validator("21")(nil)
@@ -294,7 +294,7 @@ func TestFromReaderResult_Integration(t *testing.T) {
 			Bind(func(p int) func(State) State {
 				return func(s State) State { s.parsed = p; return s }
 			}, func(s State) Validate[string, int] {
-				return FromReaderResult[string, int](parseIntRR)
+				return FromReaderResult(parseIntRR)
 			}),
 			Let[string](func(v bool) func(State) State {
 				return func(s State) State { s.valid = v; return s }
@@ -315,7 +315,7 @@ func TestFromReaderResult_EdgeCases(t *testing.T) {
 			return result.Of(input)
 		}
 
-		validator := FromReaderResult[int, int](successRR)
+		validator := FromReaderResult(successRR)
 		validationResult := validator(42)(nil)
 
 		assert.True(t, either.IsRight(validationResult))
@@ -326,7 +326,7 @@ func TestFromReaderResult_EdgeCases(t *testing.T) {
 			return result.Of(input)
 		}
 
-		validator := FromReaderResult[string, string](identityRR)
+		validator := FromReaderResult(identityRR)
 		validationResult := validator("")(nil)
 
 		assert.Equal(t, validation.Success(""), validationResult)
@@ -337,7 +337,7 @@ func TestFromReaderResult_EdgeCases(t *testing.T) {
 			return result.Of(input)
 		}
 
-		validator := FromReaderResult[int, int](identityRR)
+		validator := FromReaderResult(identityRR)
 		validationResult := validator(0)(nil)
 
 		assert.Equal(t, validation.Success(0), validationResult)
@@ -352,7 +352,7 @@ func TestFromReaderResult_EdgeCases(t *testing.T) {
 			return result.Of(&Data{Value: input})
 		}
 
-		validator := FromReaderResult[int, *Data](createDataRR)
+		validator := FromReaderResult(createDataRR)
 		validationResult := validator(42)(nil)
 
 		assert.True(t, either.IsRight(validationResult))
@@ -372,7 +372,7 @@ func TestFromReaderResult_EdgeCases(t *testing.T) {
 			return result.Of([]string{input, input})
 		}
 
-		validator := FromReaderResult[string, []string](splitRR)
+		validator := FromReaderResult(splitRR)
 		validationResult := validator("test")(nil)
 
 		assert.Equal(t, validation.Success([]string{"test", "test"}), validationResult)
@@ -383,7 +383,7 @@ func TestFromReaderResult_EdgeCases(t *testing.T) {
 			return result.Of(map[string]int{input: len(input)})
 		}
 
-		validator := FromReaderResult[string, map[string]int](createMapRR)
+		validator := FromReaderResult(createMapRR)
 		validationResult := validator("hello")(nil)
 
 		assert.Equal(t, validation.Success(map[string]int{"hello": 5}), validationResult)
@@ -398,7 +398,7 @@ func TestFromReaderResult_TypeSafety(t *testing.T) {
 			return result.Of(fmt.Sprintf("%d", input))
 		}
 
-		validator := FromReaderResult[int, string](intToStringRR)
+		validator := FromReaderResult(intToStringRR)
 
 		// This should compile and work correctly
 		validationResult := validator(42)(nil)
@@ -409,7 +409,7 @@ func TestFromReaderResult_TypeSafety(t *testing.T) {
 		// This test verifies that the output type is preserved
 		stringToIntRR := result.Eitherize1(strconv.Atoi)
 
-		validator := FromReaderResult[string, int](stringToIntRR)
+		validator := FromReaderResult(stringToIntRR)
 		validationResult := validator("42")(nil)
 
 		// The result should be Validation[int]
@@ -428,7 +428,7 @@ func TestFromReaderResult_TypeSafety(t *testing.T) {
 			return Output{Result: val}, nil
 		})
 
-		validator := FromReaderResult[Input, Output](transformRR)
+		validator := FromReaderResult(transformRR)
 		validationResult := validator(Input{Value: "42"})(nil)
 
 		assert.Equal(t, validation.Success(Output{Result: 42}), validationResult)
@@ -441,7 +441,7 @@ func BenchmarkFromReaderResult_Success(b *testing.B) {
 		return result.Of(input * 2)
 	}
 
-	validator := FromReaderResult[int, int](successRR)
+	validator := FromReaderResult(successRR)
 
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
@@ -455,7 +455,7 @@ func BenchmarkFromReaderResult_Failure(b *testing.B) {
 		return result.Left[int](errors.New("error"))
 	}
 
-	validator := FromReaderResult[int, int](failureRR)
+	validator := FromReaderResult(failureRR)
 
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
@@ -469,7 +469,7 @@ func BenchmarkFromReaderResult_WithContext(b *testing.B) {
 		return result.Of(input * 2)
 	}
 
-	validator := FromReaderResult[int, int](successRR)
+	validator := FromReaderResult(successRR)
 	ctx := Context{
 		{Key: "user", Type: "User"},
 		{Key: "age", Type: "int"},

v2/optics/codec/validate/monad_test.go

@@ -26,7 +26,7 @@ func TestMonadChainLeft(t *testing.T) {
 		handler := func(errs Errors) Validate[string, int] {
 			for _, err := range errs {
 				if err.Messsage == "validation failed" {
-					return Of[string, int](0) // recover with default
+					return Of[string](0) // recover with default
 				}
 			}
 			return func(input string) Reader[Context, Validation[int]] {
@@ -43,7 +43,7 @@ func TestMonadChainLeft(t *testing.T) {
 	})
 
 	t.Run("preserves success values unchanged", func(t *testing.T) {
-		successValidator := Of[string, int](42)
+		successValidator := Of[string](42)
 
 		handler := func(errs Errors) Validate[string, int] {
 			return func(input string) Reader[Context, Validation[int]] {
@@ -145,7 +145,7 @@ func TestMonadChainLeft(t *testing.T) {
 		}
 
 		handler := func(errs Errors) Validate[Config, string] {
-			return Of[Config, string]("default-value")
+			return Of[Config]("default-value")
 		}
 
 		validator := MonadChainLeft(failingValidator, handler)
@@ -194,7 +194,7 @@ func TestMonadChainLeft(t *testing.T) {
 		}
 
 		handler := func(errs Errors) Validate[string, int] {
-			return Of[string, int](42)
+			return Of[string](42)
 		}
 
 		// MonadChainLeft - direct application
@@ -229,7 +229,7 @@ func TestMonadChainLeft(t *testing.T) {
 			// Check if we can recover
 			for _, err := range errs {
 				if err.Messsage == "error1" {
-					return Of[string, int](100) // recover
+					return Of[string](100) // recover
 				}
 			}
 			return func(input string) Reader[Context, Validation[int]] {
@@ -248,12 +248,12 @@ func TestMonadChainLeft(t *testing.T) {
 	})
 
 	t.Run("does not call handler on success", func(t *testing.T) {
-		successValidator := Of[string, int](42)
+		successValidator := Of[string](42)
 		handlerCalled := false
 
 		handler := func(errs Errors) Validate[string, int] {
 			handlerCalled = true
-			return Of[string, int](0)
+			return Of[string](0)
 		}
 
 		validator := MonadChainLeft(successValidator, handler)
@@ -267,9 +267,9 @@ func TestMonadChainLeft(t *testing.T) {
 // TestMonadAlt tests the MonadAlt function
 func TestMonadAlt(t *testing.T) {
 	t.Run("returns first validator when it succeeds", func(t *testing.T) {
-		validator1 := Of[string, int](42)
+		validator1 := Of[string](42)
 		validator2 := func() Validate[string, int] {
-			return Of[string, int](100)
+			return Of[string](100)
 		}
 
 		result := MonadAlt(validator1, validator2)("input")(nil)
@@ -285,7 +285,7 @@ func TestMonadAlt(t *testing.T) {
 			}
 		}
 		fallback := func() Validate[string, int] {
-			return Of[string, int](42)
+			return Of[string](42)
 		}
 
 		result := MonadAlt(failing, fallback)("input")(nil)
@@ -328,11 +328,11 @@ func TestMonadAlt(t *testing.T) {
 	})
 
 	t.Run("does not evaluate second validator when first succeeds", func(t *testing.T) {
-		validator1 := Of[string, int](42)
+		validator1 := Of[string](42)
 		evaluated := false
 		validator2 := func() Validate[string, int] {
 			evaluated = true
-			return Of[string, int](100)
+			return Of[string](100)
 		}
 
 		result := MonadAlt(validator1, validator2)("input")(nil)
@@ -349,7 +349,7 @@ func TestMonadAlt(t *testing.T) {
 			}
 		}
 		fallback := func() Validate[string, string] {
-			return Of[string, string]("fallback")
+			return Of[string]("fallback")
 		}
 
 		result := MonadAlt(failing, fallback)("input")(nil)
@@ -374,7 +374,7 @@ func TestMonadAlt(t *testing.T) {
 			}
 		}
 		succeeding := func() Validate[string, int] {
-			return Of[string, int](42)
+			return Of[string](42)
 		}
 
 		// Chain: try failing1, then failing2, then succeeding
@@ -395,7 +395,7 @@ func TestMonadAlt(t *testing.T) {
 			}
 		}
 		fallback := func() Validate[Config, string] {
-			return Of[Config, string]("default")
+			return Of[Config]("default")
 		}
 
 		result := MonadAlt(failing, fallback)(Config{Port: 9999})(nil)
@@ -458,9 +458,9 @@ func TestMonadAlt(t *testing.T) {
 // TestAlt tests the Alt function
 func TestAlt(t *testing.T) {
 	t.Run("returns first validator when it succeeds", func(t *testing.T) {
-		validator1 := Of[string, int](42)
+		validator1 := Of[string](42)
 		validator2 := func() Validate[string, int] {
-			return Of[string, int](100)
+			return Of[string](100)
 		}
 
 		withAlt := Alt(validator2)
@@ -477,7 +477,7 @@ func TestAlt(t *testing.T) {
 			}
 		}
 		fallback := func() Validate[string, int] {
-			return Of[string, int](42)
+			return Of[string](42)
 		}
 
 		withAlt := Alt(fallback)
@@ -522,11 +522,11 @@ func TestAlt(t *testing.T) {
 	})
 
 	t.Run("does not evaluate second validator when first succeeds", func(t *testing.T) {
-		validator1 := Of[string, int](42)
+		validator1 := Of[string](42)
 		evaluated := false
 		validator2 := func() Validate[string, int] {
 			evaluated = true
-			return Of[string, int](100)
+			return Of[string](100)
 		}
 
 		withAlt := Alt(validator2)
@@ -553,7 +553,7 @@ func TestAlt(t *testing.T) {
 			}
 		}
 		succeeding := func() Validate[string, int] {
-			return Of[string, int](42)
+			return Of[string](42)
 		}
 
 		// Use F.Pipe to chain alternatives
@@ -576,7 +576,7 @@ func TestAlt(t *testing.T) {
 			}
 		}
 		fallback := func() Validate[string, int] {
-			return Of[string, int](42)
+			return Of[string](42)
 		}
 
 		// Alt - curried for pipelines
@@ -592,9 +592,9 @@ func TestAlt(t *testing.T) {
 // TestMonadAltAndAltEquivalence tests that MonadAlt and Alt are equivalent
 func TestMonadAltAndAltEquivalence(t *testing.T) {
 	t.Run("both produce same results for success", func(t *testing.T) {
-		validator1 := Of[string, int](42)
+		validator1 := Of[string](42)
 		validator2 := func() Validate[string, int] {
-			return Of[string, int](100)
+			return Of[string](100)
 		}
 
 		resultMonadAlt := MonadAlt(validator1, validator2)("input")(nil)
@@ -612,7 +612,7 @@ func TestMonadAltAndAltEquivalence(t *testing.T) {
 			}
 		}
 		fallback := func() Validate[string, int] {
-			return Of[string, int](42)
+			return Of[string](42)
 		}
 
 		resultMonadAlt := MonadAlt(failing, fallback)("input")(nil)

v2/optics/codec/validate/monoid_test.go

@@ -15,7 +15,7 @@ import (
 // TestAlternativeMonoid tests the AlternativeMonoid function
 func TestAlternativeMonoid(t *testing.T) {
 	t.Run("with string monoid", func(t *testing.T) {
-		m := AlternativeMonoid[string, string](S.Monoid)
+		m := AlternativeMonoid[string](S.Monoid)
 
 		t.Run("empty returns validator that succeeds with empty string", func(t *testing.T) {
 			empty := m.Empty()
@@ -25,8 +25,8 @@ func TestAlternativeMonoid(t *testing.T) {
 		})
 
 		t.Run("concat combines successful validators using monoid", func(t *testing.T) {
-			validator1 := Of[string, string]("Hello")
-			validator2 := Of[string, string](" World")
+			validator1 := Of[string]("Hello")
+			validator2 := Of[string](" World")
 
 			combined := m.Concat(validator1, validator2)
 			result := combined("input")(nil)
@@ -42,7 +42,7 @@ func TestAlternativeMonoid(t *testing.T) {
 					})
 				}
 			}
-			succeeding := Of[string, string]("fallback")
+			succeeding := Of[string]("fallback")
 
 			combined := m.Concat(failing, succeeding)
 			result := combined("input")(nil)
@@ -85,7 +85,7 @@ func TestAlternativeMonoid(t *testing.T) {
 		})
 
 		t.Run("concat with empty preserves validator", func(t *testing.T) {
-			validator := Of[string, string]("test")
+			validator := Of[string]("test")
 			empty := m.Empty()
 
 			result1 := m.Concat(validator, empty)("input")(nil)
@@ -110,7 +110,7 @@ func TestAlternativeMonoid(t *testing.T) {
 			func(a, b int) int { return a + b },
 			0,
 		)
-		m := AlternativeMonoid[string, int](intMonoid)
+		m := AlternativeMonoid[string](intMonoid)
 
 		t.Run("empty returns validator with zero", func(t *testing.T) {
 			empty := m.Empty()
@@ -124,8 +124,8 @@ func TestAlternativeMonoid(t *testing.T) {
 		})
 
 		t.Run("concat combines decoded values when both succeed", func(t *testing.T) {
-			validator1 := Of[string, int](10)
-			validator2 := Of[string, int](32)
+			validator1 := Of[string](10)
+			validator2 := Of[string](32)
 
 			combined := m.Concat(validator1, validator2)
 			result := combined("input")(nil)
@@ -145,7 +145,7 @@ func TestAlternativeMonoid(t *testing.T) {
 					})
 				}
 			}
-			succeeding := Of[string, int](42)
+			succeeding := Of[string](42)
 
 			combined := m.Concat(failing, succeeding)
 			result := combined("input")(nil)
@@ -158,10 +158,10 @@ func TestAlternativeMonoid(t *testing.T) {
 		})
 
 		t.Run("multiple concat operations", func(t *testing.T) {
-			validator1 := Of[string, int](1)
-			validator2 := Of[string, int](2)
-			validator3 := Of[string, int](3)
-			validator4 := Of[string, int](4)
+			validator1 := Of[string](1)
+			validator2 := Of[string](2)
+			validator3 := Of[string](3)
+			validator4 := Of[string](4)
 
 			combined := m.Concat(m.Concat(m.Concat(validator1, validator2), validator3), validator4)
 			result := combined("input")(nil)
@@ -175,11 +175,11 @@ func TestAlternativeMonoid(t *testing.T) {
 	})
 
 	t.Run("satisfies monoid laws", func(t *testing.T) {
-		m := AlternativeMonoid[string, string](S.Monoid)
+		m := AlternativeMonoid[string](S.Monoid)
 
-		validator1 := Of[string, string]("a")
-		validator2 := Of[string, string]("b")
-		validator3 := Of[string, string]("c")
+		validator1 := Of[string]("a")
+		validator2 := Of[string]("b")
+		validator3 := Of[string]("c")
 
 		t.Run("left identity", func(t *testing.T) {
 			result := m.Concat(m.Empty(), validator1)("input")(nil)
@@ -222,7 +222,7 @@ func TestAlternativeMonoid(t *testing.T) {
 func TestAltMonoid(t *testing.T) {
 	t.Run("with default value as zero", func(t *testing.T) {
 		m := AltMonoid(func() Validate[string, int] {
-			return Of[string, int](0)
+			return Of[string](0)
 		})
 
 		t.Run("empty returns the provided zero validator", func(t *testing.T) {
@@ -233,8 +233,8 @@ func TestAltMonoid(t *testing.T) {
 		})
 
 		t.Run("concat returns first validator when it succeeds", func(t *testing.T) {
-			validator1 := Of[string, int](42)
-			validator2 := Of[string, int](100)
+			validator1 := Of[string](42)
+			validator2 := Of[string](100)
 
 			combined := m.Concat(validator1, validator2)
 			result := combined("input")(nil)
@@ -250,7 +250,7 @@ func TestAltMonoid(t *testing.T) {
 					})
 				}
 			}
-			succeeding := Of[string, int](42)
+			succeeding := Of[string](42)
 
 			combined := m.Concat(failing, succeeding)
 			result := combined("input")(nil)
@@ -341,7 +341,7 @@ func TestAltMonoid(t *testing.T) {
 
 	t.Run("chaining multiple fallbacks", func(t *testing.T) {
 		m := AltMonoid(func() Validate[string, string] {
-			return Of[string, string]("default")
+			return Of[string]("default")
 		})
 
 		primary := func(input string) Reader[Context, Validation[string]] {
@@ -358,7 +358,7 @@ func TestAltMonoid(t *testing.T) {
 				})
 			}
 		}
-		tertiary := Of[string, string]("tertiary value")
+		tertiary := Of[string]("tertiary value")
 
 		combined := m.Concat(m.Concat(primary, secondary), tertiary)
 		result := combined("input")(nil)
@@ -369,14 +369,14 @@ func TestAltMonoid(t *testing.T) {
 	t.Run("difference from AlternativeMonoid", func(t *testing.T) {
 		// AltMonoid - first success wins
 		altM := AltMonoid(func() Validate[string, int] {
-			return Of[string, int](0)
+			return Of[string](0)
 		})
 
 		// AlternativeMonoid - combines successes
-		altMonoid := AlternativeMonoid[string, int](N.MonoidSum[int]())
+		altMonoid := AlternativeMonoid[string](N.MonoidSum[int]())
 
-		validator1 := Of[string, int](10)
-		validator2 := Of[string, int](32)
+		validator1 := Of[string](10)
+		validator2 := Of[string](32)
 
 		// AltMonoid: returns first success (10)
 		result1 := altM.Concat(validator1, validator2)("input")(nil)

v2/optics/prism/prisms_test.go

@@ -1405,7 +1405,7 @@ func TestFromResult(t *testing.T) {
 	t.Run("extract from successful result", func(t *testing.T) {
 		prism := FromResult[int]()
 
-		success := result.Of[int](42)
+		success := result.Of(42)
 		extracted := prism.GetOption(success)
 
 		assert.True(t, O.IsSome(extracted))
@@ -1435,7 +1435,7 @@ func TestFromResult(t *testing.T) {
 	t.Run("works with string type", func(t *testing.T) {
 		prism := FromResult[string]()
 
-		success := result.Of[string]("hello")
+		success := result.Of("hello")
 		extracted := prism.GetOption(success)
 
 		assert.True(t, O.IsSome(extracted))
@@ -1451,7 +1451,7 @@ func TestFromResult(t *testing.T) {
 		prism := FromResult[Person]()
 
 		person := Person{Name: "Alice", Age: 30}
-		success := result.Of[Person](person)
+		success := result.Of(person)
 		extracted := prism.GetOption(success)
 
 		assert.True(t, O.IsSome(extracted))
@@ -1465,9 +1465,9 @@ func TestFromResult(t *testing.T) {
 func TestFromResultWithSet(t *testing.T) {
 	t.Run("set on successful result", func(t *testing.T) {
 		prism := FromResult[int]()
-		setter := Set[result.Result[int], int](200)
+		setter := Set[result.Result[int]](200)
 
-		success := result.Of[int](42)
+		success := result.Of(42)
 		updated := setter(prism)(success)
 
 		// Verify the value was updated
@@ -1478,7 +1478,7 @@ func TestFromResultWithSet(t *testing.T) {
 
 	t.Run("set on error result leaves it unchanged", func(t *testing.T) {
 		prism := FromResult[int]()
-		setter := Set[result.Result[int], int](200)
+		setter := Set[result.Result[int]](200)
 
 		failure := E.Left[int](errors.New("test error"))
 		updated := setter(prism)(failure)
@@ -1527,13 +1527,13 @@ func TestFromResultComposition(t *testing.T) {
 		composed := Compose[result.Result[int]](positivePrism)(FromResult[int]())
 
 		// Test with positive number
-		success := result.Of[int](42)
+		success := result.Of(42)
 		extracted := composed.GetOption(success)
 		assert.True(t, O.IsSome(extracted))
 		assert.Equal(t, 42, O.GetOrElse(F.Constant(-1))(extracted))
 
 		// Test with negative number
-		negativeSuccess := result.Of[int](-5)
+		negativeSuccess := result.Of(-5)
 		extracted = composed.GetOption(negativeSuccess)
 		assert.True(t, O.IsNone(extracted))
 
@@ -1705,7 +1705,7 @@ func TestParseJSONWithSet(t *testing.T) {
 		originalJSON := []byte(`{"name":"Alice","age":30}`)
 		newPerson := Person{Name: "Bob", Age: 25}
 
-		setter := Set[[]byte, Person](newPerson)
+		setter := Set[[]byte](newPerson)
 		updatedJSON := setter(prism)(originalJSON)
 
 		// Parse the updated JSON
@@ -1722,7 +1722,7 @@ func TestParseJSONWithSet(t *testing.T) {
 		invalidJSON := []byte(`{invalid}`)
 		newPerson := Person{Name: "Charlie", Age: 35}
 
-		setter := Set[[]byte, Person](newPerson)
+		setter := Set[[]byte](newPerson)
 		result := setter(prism)(invalidJSON)
 
 		// Should return original unchanged since it couldn't be parsed

v2/readerio/profunctor_test.go

@@ -630,7 +630,7 @@ func TestLocalIOK(t *testing.T) {
 		}
 
 		// Compose using LocalIOK
-		adapted := LocalIOK[string, SimpleConfig, string](loadConfig)(useConfig)
+		adapted := LocalIOK[string](loadConfig)(useConfig)
 		result := adapted("config.json")()
 
 		assert.Equal(t, "localhost:8080", result)
@@ -650,7 +650,7 @@ func TestLocalIOK(t *testing.T) {
 			return io.Of(fmt.Sprintf("Processed: %d", n))
 		}
 
-		adapted := LocalIOK[string, int, string](loadData)(processData)
+		adapted := LocalIOK[string](loadData)(processData)
 		result := adapted("test")()
 
 		assert.Equal(t, "Processed: 40", result)
@@ -679,8 +679,8 @@ func TestLocalIOK(t *testing.T) {
 		}
 
 		// Compose transformations
-		step1 := LocalIOK[string, UserEnv, int](loadUser)(formatUser)
-		step2 := LocalIOK[string, int, string](parseID)(step1)
+		step1 := LocalIOK[string](loadUser)(formatUser)
+		step2 := LocalIOK[string](parseID)(step1)
 
 		result := step2("42")()
 		assert.Equal(t, "User ID: 42", result)
@@ -704,7 +704,7 @@ func TestLocalIOK(t *testing.T) {
 			return io.Of(fmt.Sprintf("Connected to %s:%d", cfg.Host, cfg.Port))
 		}
 
-		adapted := LocalIOK[string, DatabaseConfig, AppConfig](extractDB)(connectDB)
+		adapted := LocalIOK[string](extractDB)(connectDB)
 		result := adapted(AppConfig{
 			Database: DatabaseConfig{Host: "", Port: 5432},
 		})()
@@ -735,8 +735,8 @@ func TestLocalIOK(t *testing.T) {
 		}
 
 		// Compose the pipeline
-		step1 := LocalIOK[string, SimpleConfig, string](parseConfig)(useConfig)
-		step2 := LocalIOK[string, string, ConfigFile](readFile)(step1)
+		step1 := LocalIOK[string](parseConfig)(useConfig)
+		step2 := LocalIOK[string](readFile)(step1)
 
 		result := step2(ConfigFile{Path: "app.json"})()
 		assert.Equal(t, "Using example.com:9000", result)

v2/readerioeither/profunctor_test.go

@@ -149,7 +149,7 @@ func TestLocalIOK(t *testing.T) {
 		}
 
 		// Compose using LocalIOK
-		adapted := LocalIOK[string, string, SimpleConfig, string](loadConfig)(useConfig)
+		adapted := LocalIOK[string, string](loadConfig)(useConfig)
 		result := adapted("config.json")()
 
 		assert.Equal(t, E.Of[string]("Port: 8080"), result)
@@ -169,7 +169,7 @@ func TestLocalIOK(t *testing.T) {
 			return IOE.Of[string]("Processed: " + strconv.Itoa(n))
 		}
 
-		adapted := LocalIOK[string, string, int, string](loadData)(processData)
+		adapted := LocalIOK[string, string](loadData)(processData)
 		result := adapted("test")()
 
 		assert.Equal(t, E.Of[string]("Processed: 40"), result)
@@ -188,7 +188,7 @@ func TestLocalIOK(t *testing.T) {
 			return IOE.Left[string]("operation failed")
 		}
 
-		adapted := LocalIOK[string, string, SimpleConfig, string](loadConfig)(failingOperation)
+		adapted := LocalIOK[string, string](loadConfig)(failingOperation)
 		result := adapted("config.json")()
 
 		assert.Equal(t, E.Left[string]("operation failed"), result)
@@ -216,8 +216,8 @@ func TestLocalIOK(t *testing.T) {
 		}
 
 		// Compose transformations
-		step1 := LocalIOK[string, string, SimpleConfig, int](loadConfig)(formatConfig)
-		step2 := LocalIOK[string, string, int, string](parseID)(step1)
+		step1 := LocalIOK[string, string](loadConfig)(formatConfig)
+		step2 := LocalIOK[string, string](parseID)(step1)
 
 		result := step2("42")()
 		assert.Equal(t, E.Of[string]("Port: 8042"), result)
@@ -243,7 +243,7 @@ func TestLocalIOEitherK(t *testing.T) {
 		}
 
 		// Compose using LocalIOEitherK
-		adapted := LocalIOEitherK[string, SimpleConfig, string, string](loadConfig)(useConfig)
+		adapted := LocalIOEitherK[string](loadConfig)(useConfig)
 
 		// Success case
 		result := adapted("config.json")()
@@ -265,7 +265,7 @@ func TestLocalIOEitherK(t *testing.T) {
 			return IOE.Of[string]("Port: " + strconv.Itoa(cfg.Port))
 		}
 
-		adapted := LocalIOEitherK[string, SimpleConfig, string, string](loadConfig)(useConfig)
+		adapted := LocalIOEitherK[string](loadConfig)(useConfig)
 		result := adapted("missing.json")()
 
 		// Error from loadConfig should propagate
@@ -282,7 +282,7 @@ func TestLocalIOEitherK(t *testing.T) {
 			return IOE.Left[string]("operation failed")
 		}
 
-		adapted := LocalIOEitherK[string, SimpleConfig, string, string](loadConfig)(failingOperation)
+		adapted := LocalIOEitherK[string](loadConfig)(failingOperation)
 		result := adapted("config.json")()
 
 		// Error from ReaderIOEither should propagate
@@ -317,8 +317,8 @@ func TestLocalIOEitherK(t *testing.T) {
 		}
 
 		// Compose transformations
-		step1 := LocalIOEitherK[string, SimpleConfig, int, string](loadConfig)(formatConfig)
-		step2 := LocalIOEitherK[string, int, string, string](parseID)(step1)
+		step1 := LocalIOEitherK[string](loadConfig)(formatConfig)
+		step2 := LocalIOEitherK[string](parseID)(step1)
 
 		// Success case
 		result := step2("42")()
@@ -364,8 +364,8 @@ func TestLocalIOEitherK(t *testing.T) {
 		}
 
 		// Compose the pipeline
-		step1 := LocalIOEitherK[string, SimpleConfig, string, string](parseConfig)(useConfig)
-		step2 := LocalIOEitherK[string, string, ConfigFile, string](readFile)(step1)
+		step1 := LocalIOEitherK[string](parseConfig)(useConfig)
+		step2 := LocalIOEitherK[string](readFile)(step1)
 
 		// Success case
 		result := step2(ConfigFile{Path: "app.json"})()

v2/readerioeither/reader.go

@@ -37,11 +37,46 @@ import (
 	"github.com/IBM/fp-go/v2/readeroption"
 )
 
+// FromReaderOption converts a ReaderOption to a Kleisli arrow that handles None cases.
+// When the Option is None, the provided lazy error value is used.
+//
+// # Type Parameters
+//
+//   - R: The context/environment type
+//   - A: The value type
+//   - E: The error type
+//
+// # Parameters
+//
+//   - onNone: Lazy function that provides the error value when Option is None
+//
+// # Returns
+//
+//   - Kleisli arrow that converts ReaderOption to ReaderIOEither
+//
 //go:inline
 func FromReaderOption[R, A, E any](onNone Lazy[E]) Kleisli[R, E, ReaderOption[R, A], A] {
 	return function.Bind2nd(function.Flow2[ReaderOption[R, A], IOE.Kleisli[E, Option[A], A]], IOE.FromOption[A](onNone))
 }
 
+// FromReaderIO lifts a ReaderIO into a ReaderIOEither, placing the result in the Right side.
+// This is an alias for RightReaderIO, converting a computation that cannot fail into one
+// that can fail but never does.
+//
+// # Type Parameters
+//
+//   - E: The error type (will never actually contain an error)
+//   - R: The context/environment type
+//   - A: The value type
+//
+// # Parameters
+//
+//   - ma: The ReaderIO to lift
+//
+// # Returns
+//
+//   - ReaderIOEither with the ReaderIO result in the Right side
+//
 //go:inline
 func FromReaderIO[E, R, A any](ma ReaderIO[R, A]) ReaderIOEither[R, E, A] {
 	return RightReaderIO[E](ma)
@@ -121,6 +156,26 @@ func MonadChainFirst[R, E, A, B any](fa ReaderIOEither[R, E, A], f Kleisli[R, E,
 		f)
 }
 
+// MonadTap is an alias for MonadChainFirst.
+// It sequences two computations but keeps the result of the first, emphasizing the
+// side-effect nature of the operation (like "tapping" into a pipeline).
+//
+// # Type Parameters
+//
+//   - R: The context/environment type
+//   - E: The error type
+//   - A: The input value type (preserved in output)
+//   - B: The side effect result type (discarded)
+//
+// # Parameters
+//
+//   - fa: The ReaderIOEither computation
+//   - f: The side effect Kleisli arrow
+//
+// # Returns
+//
+//   - ReaderIOEither with the original value preserved
+//
 //go:inline
 func MonadTap[R, E, A, B any](fa ReaderIOEither[R, E, A], f Kleisli[R, E, A, B]) ReaderIOEither[R, E, A] {
 	return MonadChainFirst(fa, f)
@@ -165,6 +220,26 @@ func MonadChainFirstEitherK[R, E, A, B any](ma ReaderIOEither[R, E, A], f either
 	)
 }
 
+// MonadTapEitherK is an alias for MonadChainFirstEitherK.
+// It chains an Either-returning computation while preserving the original value,
+// emphasizing the side-effect nature of the operation.
+//
+// # Type Parameters
+//
+//   - R: The context/environment type
+//   - E: The error type
+//   - A: The input value type (preserved in output)
+//   - B: The side effect result type (discarded)
+//
+// # Parameters
+//
+//   - ma: The ReaderIOEither computation
+//   - f: The Either-returning side effect function
+//
+// # Returns
+//
+//   - ReaderIOEither with the original value preserved
+//
 //go:inline
 func MonadTapEitherK[R, E, A, B any](ma ReaderIOEither[R, E, A], f either.Kleisli[E, A, B]) ReaderIOEither[R, E, A] {
 	return MonadChainFirstEitherK(ma, f)
@@ -183,6 +258,25 @@ func ChainFirstEitherK[R, E, A, B any](f either.Kleisli[E, A, B]) Operator[R, E,
 	)
 }
 
+// TapEitherK is an alias for ChainFirstEitherK.
+// It returns a function that chains an Either-returning side effect while preserving
+// the original value, emphasizing the "tap" pattern for observing values.
+//
+// # Type Parameters
+//
+//   - R: The context/environment type
+//   - E: The error type
+//   - A: The input value type (preserved in output)
+//   - B: The side effect result type (discarded)
+//
+// # Parameters
+//
+//   - f: The Either-returning side effect function
+//
+// # Returns
+//
+//   - Operator that executes the side effect while preserving the original value
+//
 //go:inline
 func TapEitherK[R, E, A, B any](f either.Kleisli[E, A, B]) Operator[R, E, A, A] {
 	return ChainFirstEitherK[R](f)
@@ -213,6 +307,26 @@ func ChainReaderK[E, R, A, B any](f reader.Kleisli[R, A, B]) Operator[R, E, A, B
 	)
 }
 
+// MonadChainFirstReaderK chains a Reader-returning computation while preserving the original value.
+// Useful for performing Reader-based side effects (like logging with context) while keeping
+// the original value.
+//
+// # Type Parameters
+//
+//   - E: The error type
+//   - R: The context/environment type
+//   - A: The input value type (preserved in output)
+//   - B: The side effect result type (discarded)
+//
+// # Parameters
+//
+//   - ma: The ReaderIOEither computation
+//   - f: The Reader-returning side effect function
+//
+// # Returns
+//
+//   - ReaderIOEither with the original value preserved
+//
 //go:inline
 func MonadChainFirstReaderK[E, R, A, B any](ma ReaderIOEither[R, E, A], f reader.Kleisli[R, A, B]) ReaderIOEither[R, E, A] {
 	return fromreader.MonadChainFirstReaderK(
@@ -223,6 +337,25 @@ func MonadChainFirstReaderK[E, R, A, B any](ma ReaderIOEither[R, E, A], f reader
 	)
 }
 
+// MonadTapReaderK is an alias for MonadChainFirstReaderK.
+// It chains a Reader-returning side effect while preserving the original value.
+//
+// # Type Parameters
+//
+//   - E: The error type
+//   - R: The context/environment type
+//   - A: The input value type (preserved in output)
+//   - B: The side effect result type (discarded)
+//
+// # Parameters
+//
+//   - ma: The ReaderIOEither computation
+//   - f: The Reader-returning side effect function
+//
+// # Returns
+//
+//   - ReaderIOEither with the original value preserved
+//
 //go:inline
 func MonadTapReaderK[E, R, A, B any](ma ReaderIOEither[R, E, A], f reader.Kleisli[R, A, B]) ReaderIOEither[R, E, A] {
 	return MonadChainFirstReaderK(ma, f)
@@ -240,11 +373,49 @@ func ChainFirstReaderK[E, R, A, B any](f reader.Kleisli[R, A, B]) Operator[R, E,
 	)
 }
 
+// TapReaderK is an alias for ChainFirstReaderK.
+// It returns a function that chains a Reader-returning side effect while preserving
+// the original value.
+//
+// # Type Parameters
+//
+//   - E: The error type
+//   - R: The context/environment type
+//   - A: The input value type (preserved in output)
+//   - B: The side effect result type (discarded)
+//
+// # Parameters
+//
+//   - f: The Reader-returning side effect function
+//
+// # Returns
+//
+//   - Operator that executes the side effect while preserving the original value
+//
 //go:inline
 func TapReaderK[E, R, A, B any](f reader.Kleisli[R, A, B]) Operator[R, E, A, A] {
 	return ChainFirstReaderK[E](f)
 }
 
+// MonadChainReaderIOK chains a ReaderIO-returning computation into a ReaderIOEither.
+// The ReaderIO is automatically lifted into the ReaderIOEither context.
+//
+// # Type Parameters
+//
+//   - E: The error type
+//   - R: The context/environment type
+//   - A: The input value type
+//   - B: The output value type
+//
+// # Parameters
+//
+//   - ma: The ReaderIOEither computation
+//   - f: The ReaderIO-returning function
+//
+// # Returns
+//
+//   - ReaderIOEither with the result of the ReaderIO computation
+//
 //go:inline
 func MonadChainReaderIOK[E, R, A, B any](ma ReaderIOEither[R, E, A], f readerio.Kleisli[R, A, B]) ReaderIOEither[R, E, B] {
 	return fromreader.MonadChainReaderK(
@@ -255,6 +426,24 @@ func MonadChainReaderIOK[E, R, A, B any](ma ReaderIOEither[R, E, A], f readerio.
 	)
 }
 
+// ChainReaderIOK returns a function that chains a ReaderIO-returning function into ReaderIOEither.
+// This is the curried version of MonadChainReaderIOK.
+//
+// # Type Parameters
+//
+//   - E: The error type
+//   - R: The context/environment type
+//   - A: The input value type
+//   - B: The output value type
+//
+// # Parameters
+//
+//   - f: The ReaderIO-returning function
+//
+// # Returns
+//
+//   - Operator that chains the ReaderIO computation
+//
 //go:inline
 func ChainReaderIOK[E, R, A, B any](f readerio.Kleisli[R, A, B]) Operator[R, E, A, B] {
 	return fromreader.ChainReaderK(
@@ -264,6 +453,25 @@ func ChainReaderIOK[E, R, A, B any](f readerio.Kleisli[R, A, B]) Operator[R, E,
 	)
 }
 
+// MonadChainFirstReaderIOK chains a ReaderIO-returning computation while preserving the original value.
+// Useful for performing ReaderIO-based side effects while keeping the original value.
+//
+// # Type Parameters
+//
+//   - E: The error type
+//   - R: The context/environment type
+//   - A: The input value type (preserved in output)
+//   - B: The side effect result type (discarded)
+//
+// # Parameters
+//
+//   - ma: The ReaderIOEither computation
+//   - f: The ReaderIO-returning side effect function
+//
+// # Returns
+//
+//   - ReaderIOEither with the original value preserved
+//
 //go:inline
 func MonadChainFirstReaderIOK[E, R, A, B any](ma ReaderIOEither[R, E, A], f readerio.Kleisli[R, A, B]) ReaderIOEither[R, E, A] {
 	return fromreader.MonadChainFirstReaderK(
@@ -274,11 +482,48 @@ func MonadChainFirstReaderIOK[E, R, A, B any](ma ReaderIOEither[R, E, A], f read
 	)
 }
 
+// MonadTapReaderIOK is an alias for MonadChainFirstReaderIOK.
+// It chains a ReaderIO-returning side effect while preserving the original value.
+//
+// # Type Parameters
+//
+//   - E: The error type
+//   - R: The context/environment type
+//   - A: The input value type (preserved in output)
+//   - B: The side effect result type (discarded)
+//
+// # Parameters
+//
+//   - ma: The ReaderIOEither computation
+//   - f: The ReaderIO-returning side effect function
+//
+// # Returns
+//
+//   - ReaderIOEither with the original value preserved
+//
 //go:inline
 func MonadTapReaderIOK[E, R, A, B any](ma ReaderIOEither[R, E, A], f readerio.Kleisli[R, A, B]) ReaderIOEither[R, E, A] {
 	return MonadChainFirstReaderIOK(ma, f)
 }
 
+// ChainFirstReaderIOK returns a function that chains a ReaderIO-returning function while
+// preserving the original value. This is the curried version of MonadChainFirstReaderIOK.
+//
+// # Type Parameters
+//
+//   - E: The error type
+//   - R: The context/environment type
+//   - A: The input value type (preserved in output)
+//   - B: The side effect result type (discarded)
+//
+// # Parameters
+//
+//   - f: The ReaderIO-returning side effect function
+//
+// # Returns
+//
+//   - Operator that executes the side effect while preserving the original value
+//
 //go:inline
 func ChainFirstReaderIOK[E, R, A, B any](f readerio.Kleisli[R, A, B]) Operator[R, E, A, A] {
 	return fromreader.ChainFirstReaderK(
@@ -288,11 +533,49 @@ func ChainFirstReaderIOK[E, R, A, B any](f readerio.Kleisli[R, A, B]) Operator[R
 	)
 }
 
+// TapReaderIOK is an alias for ChainFirstReaderIOK.
+// It returns a function that chains a ReaderIO-returning side effect while preserving
+// the original value.
+//
+// # Type Parameters
+//
+//   - E: The error type
+//   - R: The context/environment type
+//   - A: The input value type (preserved in output)
+//   - B: The side effect result type (discarded)
+//
+// # Parameters
+//
+//   - f: The ReaderIO-returning side effect function
+//
+// # Returns
+//
+//   - Operator that executes the side effect while preserving the original value
+//
 //go:inline
 func TapReaderIOK[E, R, A, B any](f readerio.Kleisli[R, A, B]) Operator[R, E, A, A] {
 	return ChainFirstReaderIOK[E](f)
 }
 
+// MonadChainReaderEitherK chains a ReaderEither-returning computation into a ReaderIOEither.
+// The ReaderEither is automatically lifted into the ReaderIOEither context.
+//
+// # Type Parameters
+//
+//   - R: The context/environment type
+//   - E: The error type
+//   - A: The input value type
+//   - B: The output value type
+//
+// # Parameters
+//
+//   - ma: The ReaderIOEither computation
+//   - f: The ReaderEither-returning function
+//
+// # Returns
+//
+//   - ReaderIOEither with the result of the ReaderEither computation
+//
 //go:inline
 func MonadChainReaderEitherK[R, E, A, B any](ma ReaderIOEither[R, E, A], f RE.Kleisli[R, E, A, B]) ReaderIOEither[R, E, B] {
 	return fromreader.MonadChainReaderK(
@@ -315,6 +598,25 @@ func ChainReaderEitherK[E, R, A, B any](f RE.Kleisli[R, E, A, B]) Operator[R, E,
 	)
 }
 
+// MonadChainFirstReaderEitherK chains a ReaderEither-returning computation while preserving the original value.
+// Useful for performing ReaderEither-based side effects while keeping the original value.
+//
+// # Type Parameters
+//
+//   - R: The context/environment type
+//   - E: The error type
+//   - A: The input value type (preserved in output)
+//   - B: The side effect result type (discarded)
+//
+// # Parameters
+//
+//   - ma: The ReaderIOEither computation
+//   - f: The ReaderEither-returning side effect function
+//
+// # Returns
+//
+//   - ReaderIOEither with the original value preserved
+//
 //go:inline
 func MonadChainFirstReaderEitherK[R, E, A, B any](ma ReaderIOEither[R, E, A], f RE.Kleisli[R, E, A, B]) ReaderIOEither[R, E, A] {
 	return fromreader.MonadChainFirstReaderK(
@@ -325,6 +627,25 @@ func MonadChainFirstReaderEitherK[R, E, A, B any](ma ReaderIOEither[R, E, A], f
 	)
 }
 
+// MonadTapReaderEitherK is an alias for MonadChainFirstReaderEitherK.
+// It chains a ReaderEither-returning side effect while preserving the original value.
+//
+// # Type Parameters
+//
+//   - R: The context/environment type
+//   - E: The error type
+//   - A: The input value type (preserved in output)
+//   - B: The side effect result type (discarded)
+//
+// # Parameters
+//
+//   - ma: The ReaderIOEither computation
+//   - f: The ReaderEither-returning side effect function
+//
+// # Returns
+//
+//   - ReaderIOEither with the original value preserved
+//
 //go:inline
 func MonadTapReaderEitherK[R, E, A, B any](ma ReaderIOEither[R, E, A], f RE.Kleisli[R, E, A, B]) ReaderIOEither[R, E, A] {
 	return MonadChainFirstReaderEitherK(ma, f)
@@ -342,11 +663,48 @@ func ChainFirstReaderEitherK[E, R, A, B any](f RE.Kleisli[R, E, A, B]) Operator[
 	)
 }
 
+// TapReaderEitherK is an alias for ChainFirstReaderEitherK.
+// It returns a function that chains a ReaderEither-returning side effect while preserving
+// the original value.
+//
+// # Type Parameters
+//
+//   - E: The error type
+//   - R: The context/environment type
+//   - A: The input value type (preserved in output)
+//   - B: The side effect result type (discarded)
+//
+// # Parameters
+//
+//   - f: The ReaderEither-returning side effect function
+//
+// # Returns
+//
+//   - Operator that executes the side effect while preserving the original value
+//
 //go:inline
 func TapReaderEitherK[E, R, A, B any](f RE.Kleisli[R, E, A, B]) Operator[R, E, A, A] {
 	return ChainFirstReaderEitherK(f)
 }
 
+// ChainReaderOptionK returns a function that chains a ReaderOption-returning function into ReaderIOEither.
+// When the Option is None, the provided error value is used.
+//
+// # Type Parameters
+//
+//   - R: The context/environment type
+//   - A: The input value type
+//   - B: The output value type
+//   - E: The error type
+//
+// # Parameters
+//
+//   - onNone: Lazy function that provides the error value when Option is None
+//
+// # Returns
+//
+//   - Function that takes a ReaderOption Kleisli and returns an Operator
+//
 //go:inline
 func ChainReaderOptionK[R, A, B, E any](onNone Lazy[E]) func(readeroption.Kleisli[R, A, B]) Operator[R, E, A, B] {
 	fro := FromReaderOption[R, B](onNone)
@@ -359,6 +717,24 @@ func ChainReaderOptionK[R, A, B, E any](onNone Lazy[E]) func(readeroption.Kleisl
 	}
 }
 
+// ChainFirstReaderOptionK returns a function that chains a ReaderOption-returning function
+// while preserving the original value. When the Option is None, the provided error value is used.
+//
+// # Type Parameters
+//
+//   - R: The context/environment type
+//   - A: The input value type (preserved in output)
+//   - B: The side effect result type (discarded)
+//   - E: The error type
+//
+// # Parameters
+//
+//   - onNone: Lazy function that provides the error value when Option is None
+//
+// # Returns
+//
+//   - Function that takes a ReaderOption Kleisli and returns an Operator
+//
 //go:inline
 func ChainFirstReaderOptionK[R, A, B, E any](onNone Lazy[E]) func(readeroption.Kleisli[R, A, B]) Operator[R, E, A, A] {
 	fro := FromReaderOption[R, B](onNone)
@@ -371,6 +747,25 @@ func ChainFirstReaderOptionK[R, A, B, E any](onNone Lazy[E]) func(readeroption.K
 	}
 }
 
+// TapReaderOptionK is an alias for ChainFirstReaderOptionK.
+// It returns a function that chains a ReaderOption-returning side effect while preserving
+// the original value.
+//
+// # Type Parameters
+//
+//   - R: The context/environment type
+//   - A: The input value type (preserved in output)
+//   - B: The side effect result type (discarded)
+//   - E: The error type
+//
+// # Parameters
+//
+//   - onNone: Lazy function that provides the error value when Option is None
+//
+// # Returns
+//
+//   - Function that takes a ReaderOption Kleisli and returns an Operator
+//
 //go:inline
 func TapReaderOptionK[R, A, B, E any](onNone Lazy[E]) func(readeroption.Kleisli[R, A, B]) Operator[R, E, A, A] {
 	return ChainFirstReaderOptionK[R, A, B](onNone)
@@ -401,6 +796,110 @@ func ChainIOEitherK[R, E, A, B any](f IOE.Kleisli[E, A, B]) Operator[R, E, A, B]
 	)
 }
 
+// ChainFirstIOEitherK chains an IOEither computation while preserving the original value.
+// This is useful for performing side effects that may fail (like logging, validation, or
+// external API calls) while keeping the original value in the success case.
+//
+// The function executes the IOEither computation but discards its result, returning the
+// original value if both computations succeed. If either computation fails, the error
+// is propagated.
+//
+// This is the curried version that returns an Operator for use in function composition.
+//
+// # Type Parameters
+//
+//   - R: The context/environment type
+//   - E: The error type
+//   - A: The input value type (preserved in output)
+//   - B: The side effect result type (discarded)
+//
+// # Parameters
+//
+//   - f: IOEither.Kleisli function that performs the side effect
+//
+// # Returns
+//
+//   - Operator that chains the side effect while preserving the original value
+//
+// # Example Usage
+//
+//	type Config struct{ LogEnabled bool }
+//
+//	logValue := func(v int) IOEither[error, string] {
+//	    return IOE.Of[error](fmt.Sprintf("Value: %d", v))
+//	}
+//
+//	pipeline := F.Pipe1(
+//	    Of[Config, error](42),
+//	    ChainFirstIOEitherK[Config](logValue),
+//	)
+//	result := pipeline(Config{LogEnabled: true})() // Right(42)
+//
+// # See Also
+//
+//   - TapIOEitherK: Alias for ChainFirstIOEitherK
+//   - ChainIOEitherK: Chains IOEither and uses its result
+//   - ChainFirstEitherK: Similar but for Either computations
+//
+//go:inline
+func ChainFirstIOEitherK[R, E, A, B any](f IOE.Kleisli[E, A, B]) Operator[R, E, A, A] {
+	return fromioeither.ChainFirstIOEitherK(
+		Chain[R, E, A, A],
+		Map[R, E, B, A],
+		FromIOEither[R, E, B],
+		f,
+	)
+}
+
+// TapIOEitherK is an alias for ChainFirstIOEitherK.
+// It executes an IOEither side effect while preserving the original value.
+//
+// The name "Tap" emphasizes the side-effect nature of the operation, similar to
+// tapping into a pipeline to observe or log values without modifying the flow.
+//
+// # Type Parameters
+//
+//   - R: The context/environment type
+//   - E: The error type
+//   - A: The input value type (preserved in output)
+//   - B: The side effect result type (discarded)
+//
+// # Parameters
+//
+//   - f: IOEither.Kleisli function that performs the side effect
+//
+// # Returns
+//
+//   - Operator that executes the side effect while preserving the original value
+//
+// # Example Usage
+//
+//	type Config struct{}
+//
+//	validatePositive := func(v int) IOEither[error, bool] {
+//	    if v > 0 {
+//	        return IOE.Of[error](true)
+//	    }
+//	    return IOE.Left[bool](errors.New("must be positive"))
+//	}
+//
+//	pipeline := F.Pipe1(
+//	    Of[Config, error](42),
+//	    TapIOEitherK[Config](validatePositive),
+//	)
+//	result := pipeline(Config{})() // Right(42) if validation passes
+//
+// # See Also
+//
+//   - ChainFirstIOEitherK: The underlying implementation
+//   - TapEitherK: Similar but for Either computations
+//   - TapIOK: Similar but for IO computations
+//
+//go:inline
+func TapIOEitherK[R, E, A, B any](f IOE.Kleisli[E, A, B]) Operator[R, E, A, A] {
+	return ChainFirstIOEitherK[R](f)
+}
+
 // MonadChainIOK chains an IO-returning computation into a ReaderIOEither.
 // The IO is automatically lifted into the ReaderIOEither context (always succeeds).
 //
@@ -440,6 +939,25 @@ func MonadChainFirstIOK[R, E, A, B any](ma ReaderIOEither[R, E, A], f io.Kleisli
 	)
 }
 
+// MonadTapIOK is an alias for MonadChainFirstIOK.
+// It chains an IO-returning side effect while preserving the original value.
+//
+// # Type Parameters
+//
+//   - R: The context/environment type
+//   - E: The error type
+//   - A: The input value type (preserved in output)
+//   - B: The side effect result type (discarded)
+//
+// # Parameters
+//
+//   - ma: The ReaderIOEither computation
+//   - f: The IO-returning side effect function
+//
+// # Returns
+//
+//   - ReaderIOEither with the original value preserved
+//
 //go:inline
 func MonadTapIOK[R, E, A, B any](ma ReaderIOEither[R, E, A], f io.Kleisli[A, B]) ReaderIOEither[R, E, A] {
 	return MonadChainFirstIOK(ma, f)
@@ -458,6 +976,25 @@ func ChainFirstIOK[R, E, A, B any](f io.Kleisli[A, B]) Operator[R, E, A, A] {
 	)
 }
 
+// TapIOK is an alias for ChainFirstIOK.
+// It returns a function that chains an IO-returning side effect while preserving
+// the original value.
+//
+// # Type Parameters
+//
+//   - R: The context/environment type
+//   - E: The error type
+//   - A: The input value type (preserved in output)
+//   - B: The side effect result type (discarded)
+//
+// # Parameters
+//
+//   - f: The IO-returning side effect function
+//
+// # Returns
+//
+//   - Operator that executes the side effect while preserving the original value
+//
 //go:inline
 func TapIOK[R, E, A, B any](f io.Kleisli[A, B]) Operator[R, E, A, A] {
 	return ChainFirstIOK[R, E](f)
@@ -540,6 +1077,25 @@ func ChainFirst[R, E, A, B any](f Kleisli[R, E, A, B]) Operator[R, E, A, A] {
 		f)
 }
 
+// Tap is an alias for ChainFirst.
+// It returns a function that sequences computations but keeps the first result,
+// emphasizing the side-effect nature of the operation.
+//
+// # Type Parameters
+//
+//   - R: The context/environment type
+//   - E: The error type
+//   - A: The input value type (preserved in output)
+//   - B: The side effect result type (discarded)
+//
+// # Parameters
+//
+//   - f: The Kleisli arrow for the side effect
+//
+// # Returns
+//
+//   - Operator that executes the side effect while preserving the original value
+//
 //go:inline
 func Tap[R, E, A, B any](f Kleisli[R, E, A, B]) Operator[R, E, A, A] {
 	return ChainFirst(f)

v2/readerioeither/reader_test.go

@@ -733,3 +733,390 @@ func TestChainLeftIdenticalToOrElse(t *testing.T) {
 		assert.Equal(t, cfg, *chainLeftCfg)
 	})
 }
+
+func TestChainFirstIOEitherK(t *testing.T) {
+	type Config struct {
+		logEnabled bool
+	}
+
+	t.Run("Success - preserves original value", func(t *testing.T) {
+		sideEffectRan := false
+
+		logValue := func(v int) IOE.IOEither[error, string] {
+			return func() E.Either[error, string] {
+				sideEffectRan = true
+				return E.Right[error](fmt.Sprintf("Logged: %d", v))
+			}
+		}
+
+		pipeline := F.Pipe1(
+			Of[Config, error](42),
+			ChainFirstIOEitherK[Config](logValue),
+		)
+
+		result := pipeline(Config{logEnabled: true})()
+		assert.Equal(t, E.Right[error](42), result)
+		assert.True(t, sideEffectRan)
+	})
+
+	t.Run("Success - side effect result is discarded", func(t *testing.T) {
+		sideEffect := func(v int) IOE.IOEither[error, string] {
+			return IOE.Of[error]("side effect result")
+		}
+
+		pipeline := F.Pipe1(
+			Of[Config, error](100),
+			ChainFirstIOEitherK[Config](sideEffect),
+		)
+
+		result := pipeline(Config{})()
+		assert.Equal(t, E.Right[error](100), result)
+	})
+
+	t.Run("Failure - side effect fails", func(t *testing.T) {
+		sideEffectError := errors.New("side effect failed")
+
+		failingSideEffect := func(v int) IOE.IOEither[error, string] {
+			return IOE.Left[string](sideEffectError)
+		}
+
+		pipeline := F.Pipe1(
+			Of[Config, error](42),
+			ChainFirstIOEitherK[Config](failingSideEffect),
+		)
+
+		result := pipeline(Config{})()
+		assert.Equal(t, E.Left[int](sideEffectError), result)
+	})
+
+	t.Run("Failure - original computation fails", func(t *testing.T) {
+		originalError := errors.New("original failed")
+		sideEffectRan := false
+
+		sideEffect := func(v int) IOE.IOEither[error, string] {
+			return func() E.Either[error, string] {
+				sideEffectRan = true
+				return E.Right[error]("logged")
+			}
+		}
+
+		pipeline := F.Pipe1(
+			Left[Config, int](originalError),
+			ChainFirstIOEitherK[Config](sideEffect),
+		)
+
+		result := pipeline(Config{})()
+		assert.Equal(t, E.Left[int](originalError), result)
+		assert.False(t, sideEffectRan, "Side effect should not run when original computation fails")
+	})
+
+	t.Run("Chaining multiple side effects", func(t *testing.T) {
+		log1Ran := false
+		log2Ran := false
+
+		log1 := func(v int) IOE.IOEither[error, string] {
+			return func() E.Either[error, string] {
+				log1Ran = true
+				return E.Right[error]("log1")
+			}
+		}
+
+		log2 := func(v int) IOE.IOEither[error, string] {
+			return func() E.Either[error, string] {
+				log2Ran = true
+				return E.Right[error]("log2")
+			}
+		}
+
+		pipeline := F.Pipe2(
+			Of[Config, error](42),
+			ChainFirstIOEitherK[Config](log1),
+			ChainFirstIOEitherK[Config](log2),
+		)
+
+		result := pipeline(Config{})()
+		assert.Equal(t, E.Right[error](42), result)
+		assert.True(t, log1Ran)
+		assert.True(t, log2Ran)
+	})
+
+	t.Run("Integration with Map", func(t *testing.T) {
+		validate := func(v int) IOE.IOEither[error, bool] {
+			if v > 0 {
+				return IOE.Of[error](true)
+			}
+			return IOE.Left[bool](errors.New("must be positive"))
+		}
+
+		pipeline := F.Pipe2(
+			Of[Config, error](10),
+			ChainFirstIOEitherK[Config](validate),
+			Map[Config, error](func(x int) int { return x * 2 }),
+		)
+
+		result := pipeline(Config{})()
+		assert.Equal(t, E.Right[error](20), result)
+	})
+
+	t.Run("Different types for input and side effect result", func(t *testing.T) {
+		convertToString := func(v int) IOE.IOEither[error, string] {
+			return IOE.Of[error](fmt.Sprintf("Value: %d", v))
+		}
+
+		pipeline := F.Pipe1(
+			Of[Config, error](123),
+			ChainFirstIOEitherK[Config](convertToString),
+		)
+
+		result := pipeline(Config{})()
+		assert.Equal(t, E.Right[error](123), result)
+	})
+
+	t.Run("With context-dependent side effect", func(t *testing.T) {
+		logged := ""
+
+		logIfEnabled := func(v int) IOE.IOEither[error, string] {
+			return func() E.Either[error, string] {
+				logged = fmt.Sprintf("Logged: %d", v)
+				return E.Right[error](logged)
+			}
+		}
+
+		pipeline := F.Pipe1(
+			Of[Config, error](99),
+			ChainFirstIOEitherK[Config](logIfEnabled),
+		)
+
+		result := pipeline(Config{logEnabled: true})()
+		assert.Equal(t, E.Right[error](99), result)
+		assert.Equal(t, "Logged: 99", logged)
+	})
+}
+
+func TestTapIOEitherK(t *testing.T) {
+	type Config struct {
+		debugMode bool
+	}
+
+	t.Run("Success - preserves original value", func(t *testing.T) {
+		tapped := false
+
+		tapFunc := func(v int) IOE.IOEither[error, string] {
+			return func() E.Either[error, string] {
+				tapped = true
+				return E.Right[error](fmt.Sprintf("Tapped: %d", v))
+			}
+		}
+
+		pipeline := F.Pipe1(
+			Of[Config, error](42),
+			TapIOEitherK[Config](tapFunc),
+		)
+
+		result := pipeline(Config{})()
+		assert.Equal(t, E.Right[error](42), result)
+		assert.True(t, tapped)
+	})
+
+	t.Run("Failure - tap fails", func(t *testing.T) {
+		tapError := errors.New("tap failed")
+
+		tapFunc := func(v int) IOE.IOEither[error, string] {
+			return IOE.Left[string](tapError)
+		}
+
+		pipeline := F.Pipe1(
+			Of[Config, error](42),
+			TapIOEitherK[Config](tapFunc),
+		)
+
+		result := pipeline(Config{})()
+		assert.Equal(t, E.Left[int](tapError), result)
+	})
+
+	t.Run("Failure - original computation fails", func(t *testing.T) {
+		originalError := errors.New("original failed")
+		tapped := false
+
+		tapFunc := func(v int) IOE.IOEither[error, string] {
+			return func() E.Either[error, string] {
+				tapped = true
+				return E.Right[error]("tapped")
+			}
+		}
+
+		pipeline := F.Pipe1(
+			Left[Config, int](originalError),
+			TapIOEitherK[Config](tapFunc),
+		)
+
+		result := pipeline(Config{})()
+		assert.Equal(t, E.Left[int](originalError), result)
+		assert.False(t, tapped, "Tap should not run when original computation fails")
+	})
+
+	t.Run("Validation use case", func(t *testing.T) {
+		validatePositive := func(v int) IOE.IOEither[error, bool] {
+			if v > 0 {
+				return IOE.Of[error](true)
+			}
+			return IOE.Left[bool](errors.New("must be positive"))
+		}
+
+		pipeline := F.Pipe1(
+			Of[Config, error](42),
+			TapIOEitherK[Config](validatePositive),
+		)
+
+		result := pipeline(Config{})()
+		assert.Equal(t, E.Right[error](42), result)
+	})
+
+	t.Run("Validation failure", func(t *testing.T) {
+		validatePositive := func(v int) IOE.IOEither[error, bool] {
+			if v > 0 {
+				return IOE.Of[error](true)
+			}
+			return IOE.Left[bool](errors.New("must be positive"))
+		}
+
+		pipeline := F.Pipe1(
+			Of[Config, error](-5),
+			TapIOEitherK[Config](validatePositive),
+		)
+
+		result := pipeline(Config{})()
+		assert.True(t, E.IsLeft(result))
+	})
+
+	t.Run("Multiple taps in sequence", func(t *testing.T) {
+		tap1Ran := false
+		tap2Ran := false
+		tap3Ran := false
+
+		tap1 := func(v int) IOE.IOEither[error, string] {
+			return func() E.Either[error, string] {
+				tap1Ran = true
+				return E.Right[error]("tap1")
+			}
+		}
+
+		tap2 := func(v int) IOE.IOEither[error, string] {
+			return func() E.Either[error, string] {
+				tap2Ran = true
+				return E.Right[error]("tap2")
+			}
+		}
+
+		tap3 := func(v int) IOE.IOEither[error, string] {
+			return func() E.Either[error, string] {
+				tap3Ran = true
+				return E.Right[error]("tap3")
+			}
+		}
+
+		pipeline := F.Pipe3(
+			Of[Config, error](100),
+			TapIOEitherK[Config](tap1),
+			TapIOEitherK[Config](tap2),
+			TapIOEitherK[Config](tap3),
+		)
+
+		result := pipeline(Config{})()
+		assert.Equal(t, E.Right[error](100), result)
+		assert.True(t, tap1Ran)
+		assert.True(t, tap2Ran)
+		assert.True(t, tap3Ran)
+	})
+
+	t.Run("Tap with transformation pipeline", func(t *testing.T) {
+		tappedValue := 0
+
+		tapFunc := func(v int) IOE.IOEither[error, string] {
+			return func() E.Either[error, string] {
+				tappedValue = v
+				return E.Right[error]("tapped")
+			}
+		}
+
+		pipeline := F.Pipe3(
+			Of[Config, error](10),
+			Map[Config, error](func(x int) int { return x * 2 }),
+			TapIOEitherK[Config](tapFunc),
+			Map[Config, error](func(x int) int { return x + 5 }),
+		)
+
+		result := pipeline(Config{})()
+		assert.Equal(t, E.Right[error](25), result)
+		assert.Equal(t, 20, tappedValue)
+	})
+
+	t.Run("Tap is alias for ChainFirstIOEitherK", func(t *testing.T) {
+		// Verify that TapIOEitherK and ChainFirstIOEitherK produce identical results
+		sideEffect := func(v int) IOE.IOEither[error, string] {
+			return IOE.Of[error](fmt.Sprintf("Value: %d", v))
+		}
+
+		pipelineWithTap := F.Pipe1(
+			Of[Config, error](42),
+			TapIOEitherK[Config](sideEffect),
+		)
+
+		pipelineWithChainFirst := F.Pipe1(
+			Of[Config, error](42),
+			ChainFirstIOEitherK[Config](sideEffect),
+		)
+
+		resultTap := pipelineWithTap(Config{})()
+		resultChainFirst := pipelineWithChainFirst(Config{})()
+
+		assert.Equal(t, resultChainFirst, resultTap)
+	})
+
+	t.Run("Logging use case", func(t *testing.T) {
+		logs := []string{}
+
+		logValue := func(v int) IOE.IOEither[error, string] {
+			return func() E.Either[error, string] {
+				logMsg := fmt.Sprintf("Processing value: %d", v)
+				logs = append(logs, logMsg)
+				return E.Right[error](logMsg)
+			}
+		}
+
+		pipeline := F.Pipe2(
+			Of[Config, error](5),
+			TapIOEitherK[Config](logValue),
+			Map[Config, error](func(x int) int { return x * x }),
+		)
+
+		result := pipeline(Config{debugMode: true})()
+		assert.Equal(t, E.Right[error](25), result)
+		assert.Len(t, logs, 1)
+		assert.Equal(t, "Processing value: 5", logs[0])
+	})
+
+	t.Run("Error propagation in tap chain", func(t *testing.T) {
+		tap1 := func(v int) IOE.IOEither[error, string] {
+			return IOE.Of[error]("tap1")
+		}
+
+		tap2 := func(v int) IOE.IOEither[error, string] {
+			return IOE.Left[string](errors.New("tap2 failed"))
+		}
+
+		tap3 := func(v int) IOE.IOEither[error, string] {
+			return IOE.Of[error]("tap3")
+		}
+
+		pipeline := F.Pipe3(
+			Of[Config, error](42),
+			TapIOEitherK[Config](tap1),
+			TapIOEitherK[Config](tap2),
+			TapIOEitherK[Config](tap3),
+		)
+
+		result := pipeline(Config{})()
+		assert.True(t, E.IsLeft(result))
+	})
+}

v2/readeriooption/array_test.go

@@ -32,7 +32,7 @@ func TestTraverseArray_AllSuccess(t *testing.T) {
 	}
 
 	input := []int{1, 2, 3, 4, 5}
-	result := TraverseArray[context.Context](double)(input)
+	result := TraverseArray(double)(input)
 
 	expected := O.Of([]int{2, 4, 6, 8, 10})
 	assert.Equal(t, expected, result(context.Background())())
@@ -48,7 +48,7 @@ func TestTraverseArray_OneFailure(t *testing.T) {
 	}
 
 	input := []int{1, 2, 3, 4, 5}
-	result := TraverseArray[context.Context](failOnThree)(input)
+	result := TraverseArray(failOnThree)(input)
 
 	expected := O.None[[]int]()
 	assert.Equal(t, expected, result(context.Background())())
@@ -61,7 +61,7 @@ func TestTraverseArray_EmptyArray(t *testing.T) {
 	}
 
 	input := []int{}
-	result := TraverseArray[context.Context](double)(input)
+	result := TraverseArray(double)(input)
 
 	expected := O.Of([]int{})
 	assert.Equal(t, expected, result(context.Background())())
@@ -82,7 +82,7 @@ func TestTraverseArray_WithEnvironment(t *testing.T) {
 	}
 
 	input := []int{1, 2, 3}
-	result := TraverseArray[Config](multiply)(input)
+	result := TraverseArray(multiply)(input)
 
 	cfg := Config{Multiplier: 10}
 	expected := O.Of([]int{10, 20, 30})
@@ -105,7 +105,7 @@ func TestTraverseArray_ChainedOperation(t *testing.T) {
 
 	result := F.Pipe1(
 		Of[Config]([]int{1, 2, 3, 4}),
-		Chain(TraverseArray[Config](multiplyByFactor)),
+		Chain(TraverseArray(multiplyByFactor)),
 	)
 
 	cfg := Config{Factor: 5}
@@ -120,7 +120,7 @@ func TestTraverseArrayWithIndex_AllSuccess(t *testing.T) {
 	}
 
 	input := []string{"a", "b", "c"}
-	result := TraverseArrayWithIndex[context.Context](addIndex)(input)
+	result := TraverseArrayWithIndex(addIndex)(input)
 
 	expected := O.Of([]string{"0:a", "1:b", "2:c"})
 	assert.Equal(t, expected, result(context.Background())())
@@ -136,7 +136,7 @@ func TestTraverseArrayWithIndex_OneFailure(t *testing.T) {
 	}
 
 	input := []string{"a", "b", "c"}
-	result := TraverseArrayWithIndex[context.Context](failOnIndex)(input)
+	result := TraverseArrayWithIndex(failOnIndex)(input)
 
 	expected := O.None[[]string]()
 	assert.Equal(t, expected, result(context.Background())())
@@ -149,7 +149,7 @@ func TestTraverseArrayWithIndex_EmptyArray(t *testing.T) {
 	}
 
 	input := []string{}
-	result := TraverseArrayWithIndex[context.Context](addIndex)(input)
+	result := TraverseArrayWithIndex(addIndex)(input)
 
 	expected := O.Of([]string{})
 	assert.Equal(t, expected, result(context.Background())())
@@ -170,7 +170,7 @@ func TestTraverseArrayWithIndex_WithEnvironment(t *testing.T) {
 	}
 
 	input := []string{"a", "b", "c"}
-	result := TraverseArrayWithIndex[Config](formatWithIndex)(input)
+	result := TraverseArrayWithIndex(formatWithIndex)(input)
 
 	cfg := Config{Prefix: "item-"}
 	expected := O.Of([]string{"item-0:a", "item-1:b", "item-2:c"})
@@ -184,7 +184,7 @@ func TestTraverseArrayWithIndex_IndexUsedInLogic(t *testing.T) {
 	}
 
 	input := []int{10, 20, 30, 40}
-	result := TraverseArrayWithIndex[context.Context](multiplyByIndex)(input)
+	result := TraverseArrayWithIndex(multiplyByIndex)(input)
 
 	// 10*0=0, 20*1=20, 30*2=60, 40*3=120
 	expected := O.Of([]int{0, 20, 60, 120})
@@ -216,7 +216,7 @@ func TestTraverseArray_ComplexType(t *testing.T) {
 		{ID: 3, Name: "Charlie"},
 	}
 
-	result := TraverseArray[context.Context](loadProfile)(users)
+	result := TraverseArray(loadProfile)(users)
 
 	expected := O.Of([]UserProfile{
 		{UserID: 1, DisplayName: "Profile: Alice"},
@@ -247,12 +247,12 @@ func TestTraverseArray_ConditionalFailure(t *testing.T) {
 
 	// With MaxValue=3, should fail on 4 and 5
 	cfg1 := Config{MaxValue: 3}
-	result1 := TraverseArray[Config](validateAndDouble)(input)
+	result1 := TraverseArray(validateAndDouble)(input)
 	assert.Equal(t, O.None[[]int](), result1(cfg1)())
 
 	// With MaxValue=10, all should succeed
 	cfg2 := Config{MaxValue: 10}
-	result2 := TraverseArray[Config](validateAndDouble)(input)
+	result2 := TraverseArray(validateAndDouble)(input)
 	expected := O.Of([]int{2, 4, 6, 8, 10})
 	assert.Equal(t, expected, result2(cfg2)())
 }

v2/readeriooption/reader_test.go

@@ -67,7 +67,7 @@ func TestFromReader(t *testing.T) {
 		return cfg.Value * 2
 	}
 
-	ro := FromReader[Config](r)
+	ro := FromReader(r)
 	cfg := Config{Value: 21}
 	result := ro(cfg)()
 
@@ -83,7 +83,7 @@ func TestSomeReader(t *testing.T) {
 		return cfg.Value * 2
 	}
 
-	ro := SomeReader[Config](r)
+	ro := SomeReader(r)
 	cfg := Config{Value: 21}
 	result := ro(cfg)()
 

v2/readerioresult/reader.go

@@ -20,6 +20,7 @@ import (
 
 	"github.com/IBM/fp-go/v2/function"
 	"github.com/IBM/fp-go/v2/io"
+	"github.com/IBM/fp-go/v2/ioresult"
 	"github.com/IBM/fp-go/v2/reader"
 	RE "github.com/IBM/fp-go/v2/readereither"
 	"github.com/IBM/fp-go/v2/readerio"
@@ -28,6 +29,9 @@ import (
 	"github.com/IBM/fp-go/v2/result"
 )
 
+// FromReaderOption converts a ReaderOption to a ReaderIOResult.
+// If the ReaderOption is None, the provided function is called to produce the error.
+//
 //go:inline
 func FromReaderOption[R, A any](onNone Lazy[error]) Kleisli[R, ReaderOption[R, A], A] {
 	return RIOE.FromReaderOption[R, A](onNone)
@@ -105,6 +109,9 @@ func MonadChainFirst[R, A, B any](fa ReaderIOResult[R, A], f Kleisli[R, A, B]) R
 	return RIOE.MonadChainFirst(fa, f)
 }
 
+// MonadTap is an alias for MonadChainFirst, executing a side effect while preserving the original value.
+// The name "Tap" emphasizes the side-effect nature of the operation.
+//
 //go:inline
 func MonadTap[R, A, B any](fa ReaderIOResult[R, A], f Kleisli[R, A, B]) ReaderIOResult[R, A] {
 	return RIOE.MonadTap(fa, f)
@@ -150,6 +157,8 @@ func MonadChainFirstEitherK[R, A, B any](ma ReaderIOResult[R, A], f result.Kleis
 	return RIOE.MonadChainFirstEitherK(ma, f)
 }
 
+// MonadTapEitherK is an alias for MonadChainFirstEitherK, executing a Result side effect while preserving the original value.
+//
 //go:inline
 func MonadTapEitherK[R, A, B any](ma ReaderIOResult[R, A], f result.Kleisli[A, B]) ReaderIOResult[R, A] {
 	return RIOE.MonadTapEitherK(ma, f)
@@ -163,11 +172,43 @@ func ChainFirstEitherK[R, A, B any](f result.Kleisli[A, B]) Operator[R, A, A] {
 	return RIOE.ChainFirstEitherK[R](f)
 }
 
+// TapEitherK is an alias for ChainFirstEitherK, executing a Result side effect while preserving the original value.
+//
 //go:inline
 func TapEitherK[R, A, B any](f result.Kleisli[A, B]) Operator[R, A, A] {
 	return RIOE.TapEitherK[R](f)
 }
 
+// ChainFirstIOEitherK chains an IOResult computation while preserving the original value.
+// Useful for performing side effects that may fail while keeping the original value.
+//
+//go:inline
+func ChainFirstIOEitherK[R, A, B any](f ioresult.Kleisli[A, B]) Operator[R, A, A] {
+	return RIOE.ChainFirstIOEitherK[R](f)
+}
+
+// TapIOEitherK is an alias for ChainFirstIOEitherK, executing an IOResult side effect while preserving the original value.
+//
+//go:inline
+func TapIOEitherK[R, A, B any](f ioresult.Kleisli[A, B]) Operator[R, A, A] {
+	return RIOE.TapIOEitherK[R](f)
+}
+
+// ChainFirstIOResultK chains an IOResult computation while preserving the original value.
+// This is an alias for ChainFirstIOEitherK with more explicit naming.
+//
+//go:inline
+func ChainFirstIOResultK[R, A, B any](f ioresult.Kleisli[A, B]) Operator[R, A, A] {
+	return RIOE.ChainFirstIOEitherK[R](f)
+}
+
+// TapIOResultK is an alias for ChainFirstIOResultK, executing an IOResult side effect while preserving the original value.
+//
+//go:inline
+func TapIOResultK[R, A, B any](f ioresult.Kleisli[A, B]) Operator[R, A, A] {
+	return RIOE.TapIOEitherK[R](f)
+}
+
 // MonadChainFirstEitherK chains an Either-returning computation but keeps the original value.
 // Useful for validation or side effects that return Either.
 //
@@ -176,19 +217,23 @@ func MonadChainFirstResultK[R, A, B any](ma ReaderIOResult[R, A], f result.Kleis
 	return RIOE.MonadChainFirstEitherK(ma, f)
 }
 
+// MonadTapResultK is an alias for MonadChainFirstResultK, executing a Result side effect while preserving the original value.
+//
 //go:inline
 func MonadTapResultK[R, A, B any](ma ReaderIOResult[R, A], f result.Kleisli[A, B]) ReaderIOResult[R, A] {
 	return RIOE.MonadTapEitherK(ma, f)
 }
 
-// ChainFirstEitherK returns a function that chains an Either computation while preserving the original value.
-// This is the curried version of MonadChainFirstEitherK.
+// ChainFirstResultK returns a function that chains a Result computation while preserving the original value.
+// This is an alias for ChainFirstEitherK with more explicit naming.
 //
 //go:inline
 func ChainFirstResultK[R, A, B any](f result.Kleisli[A, B]) Operator[R, A, A] {
 	return RIOE.ChainFirstEitherK[R](f)
 }
 
+// TapResultK is an alias for ChainFirstResultK, executing a Result side effect while preserving the original value.
+//
 //go:inline
 func TapResultK[R, A, B any](f result.Kleisli[A, B]) Operator[R, A, A] {
 	return RIOE.TapEitherK[R](f)
@@ -210,36 +255,54 @@ func ChainReaderK[R, A, B any](f reader.Kleisli[R, A, B]) Operator[R, A, B] {
 	return RIOE.ChainReaderK[error](f)
 }
 
+// MonadChainFirstReaderK chains a Reader computation but keeps the original value.
+// Useful for performing Reader-based side effects while preserving the original value.
+//
 //go:inline
 func MonadChainFirstReaderK[R, A, B any](ma ReaderIOResult[R, A], f reader.Kleisli[R, A, B]) ReaderIOResult[R, A] {
 	return RIOE.MonadChainFirstReaderK(ma, f)
 }
 
+// MonadTapReaderK is an alias for MonadChainFirstReaderK, executing a Reader side effect while preserving the original value.
+//
 //go:inline
 func MonadTapReaderK[R, A, B any](ma ReaderIOResult[R, A], f reader.Kleisli[R, A, B]) ReaderIOResult[R, A] {
 	return RIOE.MonadTapReaderK(ma, f)
 }
 
+// ChainFirstReaderK returns a function that chains a Reader computation while preserving the original value.
+// This is the curried version of MonadChainFirstReaderK.
+//
 //go:inline
 func ChainFirstReaderK[R, A, B any](f reader.Kleisli[R, A, B]) Operator[R, A, A] {
 	return RIOE.ChainFirstReaderK[error](f)
 }
 
+// TapReaderK is an alias for ChainFirstReaderK, executing a Reader side effect while preserving the original value.
+//
 //go:inline
 func TapReaderK[R, A, B any](f reader.Kleisli[R, A, B]) Operator[R, A, A] {
 	return RIOE.TapReaderK[error](f)
 }
 
+// ChainReaderOptionK returns a function that chains a ReaderOption-returning function into ReaderIOResult.
+// If the ReaderOption is None, the provided error function is called.
+//
 //go:inline
 func ChainReaderOptionK[R, A, B any](onNone Lazy[error]) func(readeroption.Kleisli[R, A, B]) Operator[R, A, B] {
 	return RIOE.ChainReaderOptionK[R, A, B](onNone)
 }
 
+// ChainFirstReaderOptionK chains a ReaderOption computation while preserving the original value.
+// If the ReaderOption is None, the provided error function is called.
+//
 //go:inline
 func ChainFirstReaderOptionK[R, A, B any](onNone Lazy[error]) func(readeroption.Kleisli[R, A, B]) Operator[R, A, A] {
 	return RIOE.ChainFirstReaderOptionK[R, A, B](onNone)
 }
 
+// TapReaderOptionK is an alias for ChainFirstReaderOptionK, executing a ReaderOption side effect while preserving the original value.
+//
 //go:inline
 func TapReaderOptionK[R, A, B any](onNone Lazy[error]) func(readeroption.Kleisli[R, A, B]) Operator[R, A, A] {
 	return RIOE.TapReaderOptionK[R, A, B](onNone)
@@ -261,84 +324,123 @@ func ChainReaderEitherK[R, A, B any](f RE.Kleisli[R, error, A, B]) Operator[R, A
 	return RIOE.ChainReaderEitherK(f)
 }
 
+// MonadChainFirstReaderEitherK chains a ReaderEither computation but keeps the original value.
+// Useful for performing ReaderEither-based side effects while preserving the original value.
+//
 //go:inline
 func MonadChainFirstReaderEitherK[R, A, B any](ma ReaderIOResult[R, A], f RE.Kleisli[R, error, A, B]) ReaderIOResult[R, A] {
 	return RIOE.MonadChainFirstReaderEitherK(ma, f)
 }
 
+// MonadTapReaderEitherK is an alias for MonadChainFirstReaderEitherK, executing a ReaderEither side effect while preserving the original value.
+//
 //go:inline
 func MonadTapReaderEitherK[R, A, B any](ma ReaderIOResult[R, A], f RE.Kleisli[R, error, A, B]) ReaderIOResult[R, A] {
 	return RIOE.MonadTapReaderEitherK(ma, f)
 }
 
+// ChainFirstReaderEitherK returns a function that chains a ReaderEither computation while preserving the original value.
+// This is the curried version of MonadChainFirstReaderEitherK.
+//
 //go:inline
 func ChainFirstReaderEitherK[R, A, B any](f RE.Kleisli[R, error, A, B]) Operator[R, A, A] {
 	return RIOE.ChainFirstReaderEitherK(f)
 }
 
+// TapReaderEitherK is an alias for ChainFirstReaderEitherK, executing a ReaderEither side effect while preserving the original value.
+//
 //go:inline
 func TapReaderEitherK[R, A, B any](f RE.Kleisli[R, error, A, B]) Operator[R, A, A] {
 	return RIOE.TapReaderEitherK(f)
 }
 
+// MonadChainReaderResultK chains a ReaderResult-returning computation into a ReaderIOResult.
+// This is an alias for MonadChainReaderEitherK with more explicit naming.
+//
 //go:inline
 func MonadChainReaderResultK[R, A, B any](ma ReaderIOResult[R, A], f RE.Kleisli[R, error, A, B]) ReaderIOResult[R, B] {
 	return RIOE.MonadChainReaderEitherK(ma, f)
 }
 
-// ChainReaderK returns a function that chains a Reader-returning function into ReaderIOResult.
-// This is the curried version of MonadChainReaderK.
+// ChainReaderResultK returns a function that chains a ReaderResult-returning function into ReaderIOResult.
+// This is an alias for ChainReaderEitherK with more explicit naming.
 //
 //go:inline
 func ChainReaderResultK[R, A, B any](f RE.Kleisli[R, error, A, B]) Operator[R, A, B] {
 	return RIOE.ChainReaderEitherK(f)
 }
 
+// MonadChainFirstReaderResultK chains a ReaderResult computation but keeps the original value.
+// This is an alias for MonadChainFirstReaderEitherK with more explicit naming.
+//
 //go:inline
 func MonadChainFirstReaderResultK[R, A, B any](ma ReaderIOResult[R, A], f RE.Kleisli[R, error, A, B]) ReaderIOResult[R, A] {
 	return RIOE.MonadChainFirstReaderEitherK(ma, f)
 }
 
+// MonadTapReaderResultK is an alias for MonadChainFirstReaderResultK, executing a ReaderResult side effect while preserving the original value.
+//
 //go:inline
 func MonadTapReaderResultK[R, A, B any](ma ReaderIOResult[R, A], f RE.Kleisli[R, error, A, B]) ReaderIOResult[R, A] {
 	return RIOE.MonadTapReaderEitherK(ma, f)
 }
 
+// ChainFirstReaderResultK returns a function that chains a ReaderResult computation while preserving the original value.
+// This is an alias for ChainFirstReaderEitherK with more explicit naming.
+//
 //go:inline
 func ChainFirstReaderResultK[R, A, B any](f RE.Kleisli[R, error, A, B]) Operator[R, A, A] {
 	return RIOE.ChainFirstReaderEitherK(f)
 }
 
+// TapReaderResultK is an alias for ChainFirstReaderResultK, executing a ReaderResult side effect while preserving the original value.
+//
 //go:inline
 func TapReaderResultK[R, A, B any](f RE.Kleisli[R, error, A, B]) Operator[R, A, A] {
 	return RIOE.TapReaderEitherK(f)
 }
 
+// MonadChainReaderIOK chains a ReaderIO-returning computation into a ReaderIOResult.
+// The ReaderIO is automatically lifted into the ReaderIOResult context (always succeeds).
+//
 //go:inline
 func MonadChainReaderIOK[R, A, B any](ma ReaderIOResult[R, A], f readerio.Kleisli[R, A, B]) ReaderIOResult[R, B] {
 	return RIOE.MonadChainReaderIOK(ma, f)
 }
 
+// ChainReaderIOK returns a function that chains a ReaderIO-returning function into ReaderIOResult.
+// This is the curried version of MonadChainReaderIOK.
+//
 //go:inline
 func ChainReaderIOK[R, A, B any](f readerio.Kleisli[R, A, B]) Operator[R, A, B] {
 	return RIOE.ChainReaderIOK[error](f)
 }
 
+// MonadChainFirstReaderIOK chains a ReaderIO computation but keeps the original value.
+// Useful for performing ReaderIO-based side effects while preserving the original value.
+//
 //go:inline
 func MonadChainFirstReaderIOK[R, A, B any](ma ReaderIOResult[R, A], f readerio.Kleisli[R, A, B]) ReaderIOResult[R, A] {
 	return RIOE.MonadChainFirstReaderIOK(ma, f)
 }
 
+// MonadTapReaderIOK is an alias for MonadChainFirstReaderIOK, executing a ReaderIO side effect while preserving the original value.
+//
 //go:inline
 func MonadTapReaderIOK[R, A, B any](ma ReaderIOResult[R, A], f readerio.Kleisli[R, A, B]) ReaderIOResult[R, A] {
 	return RIOE.MonadTapReaderIOK(ma, f)
 }
 
+// ChainFirstReaderIOK returns a function that chains a ReaderIO computation while preserving the original value.
+// This is the curried version of MonadChainFirstReaderIOK.
+//
 //go:inline
 func ChainFirstReaderIOK[R, A, B any](f readerio.Kleisli[R, A, B]) Operator[R, A, A] {
 	return RIOE.ChainFirstReaderIOK[error](f)
 }
 
+// TapReaderIOK is an alias for ChainFirstReaderIOK, executing a ReaderIO side effect while preserving the original value.
+//
 //go:inline
 func TapReaderIOK[R, A, B any](f readerio.Kleisli[R, A, B]) Operator[R, A, A] {
 	return RIOE.TapReaderIOK[error](f)
@@ -400,6 +502,8 @@ func MonadChainFirstIOK[R, A, B any](ma ReaderIOResult[R, A], f func(A) IO[B]) R
 	return RIOE.MonadChainFirstIOK(ma, f)
 }
 
+// MonadTapIOK is an alias for MonadChainFirstIOK, executing an IO side effect while preserving the original value.
+//
 //go:inline
 func MonadTapIOK[R, A, B any](ma ReaderIOResult[R, A], f func(A) IO[B]) ReaderIOResult[R, A] {
 	return RIOE.MonadTapIOK(ma, f)
@@ -413,6 +517,8 @@ func ChainFirstIOK[R, A, B any](f func(A) IO[B]) Operator[R, A, A] {
 	return RIOE.ChainFirstIOK[R, error](f)
 }
 
+// TapIOK is an alias for ChainFirstIOK, executing an IO side effect while preserving the original value.
+//
 //go:inline
 func TapIOK[R, A, B any](f func(A) IO[B]) Operator[R, A, A] {
 	return RIOE.TapIOK[R, error](f)
@@ -473,6 +579,9 @@ func ChainFirst[R, A, B any](f Kleisli[R, A, B]) Operator[R, A, A] {
 	return RIOE.ChainFirst(f)
 }
 
+// Tap is an alias for ChainFirst, executing a side effect while preserving the original value.
+// The name "Tap" emphasizes the side-effect nature of the operation.
+//
 //go:inline
 func Tap[R, A, B any](f Kleisli[R, A, B]) Operator[R, A, A] {
 	return RIOE.Tap(f)
@@ -767,46 +876,70 @@ func Local[A, R1, R2 any](f func(R2) R1) func(ReaderIOResult[R1, A]) ReaderIORes
 	return RIOE.Local[error, A](f)
 }
 
+// Read executes a ReaderIOResult by providing a concrete environment value.
+// This converts a ReaderIOResult[R, A] into an IOResult[A] by supplying the R value.
+//
 //go:inline
 func Read[A, R any](r R) func(ReaderIOResult[R, A]) IOResult[A] {
 	return RIOE.Read[error, A](r)
 }
 
+// MonadChainLeft chains a computation on the error channel, allowing error recovery or transformation.
+// If the computation is successful (Right), it passes through unchanged.
+//
 //go:inline
 func MonadChainLeft[R, A any](fa ReaderIOResult[R, A], f Kleisli[R, error, A]) ReaderIOResult[R, A] {
 	return RIOE.MonadChainLeft(fa, f)
 }
 
+// ChainLeft returns a function that chains a computation on the error channel.
+// This is the curried version of MonadChainLeft.
+//
 //go:inline
 func ChainLeft[R, A any](f Kleisli[R, error, A]) func(ReaderIOResult[R, A]) ReaderIOResult[R, A] {
 	return RIOE.ChainLeft(f)
 }
 
+// MonadChainFirstLeft chains an error-handling computation but preserves the original error.
+// Useful for logging or side effects on errors without changing the error value.
+//
 //go:inline
 func MonadChainFirstLeft[A, R, B any](ma ReaderIOResult[R, A], f Kleisli[R, error, B]) ReaderIOResult[R, A] {
 	return RIOE.MonadChainFirstLeft(ma, f)
 }
 
+// MonadTapLeft is an alias for MonadChainFirstLeft, executing a side effect on errors while preserving the original error.
+//
 //go:inline
 func MonadTapLeft[A, R, B any](ma ReaderIOResult[R, A], f Kleisli[R, error, B]) ReaderIOResult[R, A] {
 	return RIOE.MonadTapLeft(ma, f)
 }
 
+// ChainFirstLeft returns a function that chains an error-handling computation while preserving the original error.
+// This is the curried version of MonadChainFirstLeft.
+//
 //go:inline
 func ChainFirstLeft[A, R, B any](f Kleisli[R, error, B]) Operator[R, A, A] {
 	return RIOE.ChainFirstLeft[A](f)
 }
 
+// ChainFirstLeftIOK chains an IO computation on errors while preserving the original error.
+// Useful for IO-based error logging or side effects.
+//
 //go:inline
 func ChainFirstLeftIOK[A, R, B any](f io.Kleisli[error, B]) Operator[R, A, A] {
 	return RIOE.ChainFirstLeftIOK[A, R](f)
 }
 
+// TapLeft is an alias for ChainFirstLeft, executing a side effect on errors while preserving the original error.
+//
 //go:inline
 func TapLeft[A, R, B any](f Kleisli[R, error, B]) Operator[R, A, A] {
 	return RIOE.TapLeft[A](f)
 }
 
+// TapLeftIOK is an alias for ChainFirstLeftIOK, executing an IO side effect on errors while preserving the original error.
+//
 //go:inline
 func TapLeftIOK[A, R, B any](f io.Kleisli[error, B]) Operator[R, A, A] {
 	return RIOE.TapLeftIOK[A, R](f)

v2/readerioresult/reader_test.go

@@ -349,7 +349,7 @@ func TestLocalIOK(t *testing.T) {
 		}
 
 		// Compose using LocalIOK
-		adapted := LocalIOK[string, SimpleConfig, string](loadConfig)(useConfig)
+		adapted := LocalIOK[string](loadConfig)(useConfig)
 		res := adapted("config.json")()
 
 		assert.Equal(t, result.Of("Port: 8080"), res)
@@ -371,7 +371,7 @@ func TestLocalIOK(t *testing.T) {
 			}
 		}
 
-		adapted := LocalIOK[string, int, string](loadData)(processData)
+		adapted := LocalIOK[string](loadData)(processData)
 		res := adapted("test")()
 
 		assert.Equal(t, result.Of("Processed: 40"), res)
@@ -392,7 +392,7 @@ func TestLocalIOK(t *testing.T) {
 			}
 		}
 
-		adapted := LocalIOK[string, SimpleConfig, string](loadConfig)(failingOperation)
+		adapted := LocalIOK[string](loadConfig)(failingOperation)
 		res := adapted("config.json")()
 
 		assert.True(t, result.IsLeft(res))
@@ -424,7 +424,7 @@ func TestLocalIOEitherK(t *testing.T) {
 		}
 
 		// Compose using LocalIOEitherK
-		adapted := LocalIOEitherK[string, SimpleConfig, string](loadConfig)(useConfig)
+		adapted := LocalIOEitherK[string](loadConfig)(useConfig)
 
 		// Success case
 		res := adapted("config.json")()
@@ -448,7 +448,7 @@ func TestLocalIOEitherK(t *testing.T) {
 			}
 		}
 
-		adapted := LocalIOEitherK[string, SimpleConfig, string](loadConfig)(useConfig)
+		adapted := LocalIOEitherK[string](loadConfig)(useConfig)
 		res := adapted("missing.json")()
 
 		// Error from loadConfig should propagate
@@ -469,7 +469,7 @@ func TestLocalIOEitherK(t *testing.T) {
 			}
 		}
 
-		adapted := LocalIOEitherK[string, SimpleConfig, string](loadConfig)(failingOperation)
+		adapted := LocalIOEitherK[string](loadConfig)(failingOperation)
 		res := adapted("config.json")()
 
 		// Error from ReaderIOResult should propagate
@@ -502,7 +502,7 @@ func TestLocalIOResultK(t *testing.T) {
 		}
 
 		// Compose using LocalIOResultK
-		adapted := LocalIOResultK[string, SimpleConfig, string](loadConfig)(useConfig)
+		adapted := LocalIOResultK[string](loadConfig)(useConfig)
 
 		// Success case
 		res := adapted("config.json")()
@@ -526,7 +526,7 @@ func TestLocalIOResultK(t *testing.T) {
 			}
 		}
 
-		adapted := LocalIOResultK[string, SimpleConfig, string](loadConfig)(useConfig)
+		adapted := LocalIOResultK[string](loadConfig)(useConfig)
 		res := adapted("missing.json")()
 
 		// Error from loadConfig should propagate
@@ -562,8 +562,8 @@ func TestLocalIOResultK(t *testing.T) {
 		}
 
 		// Compose transformations
-		step1 := LocalIOResultK[string, SimpleConfig, int](loadConfig)(formatConfig)
-		step2 := LocalIOResultK[string, int, string](parseID)(step1)
+		step1 := LocalIOResultK[string](loadConfig)(formatConfig)
+		step2 := LocalIOResultK[string](parseID)(step1)
 
 		// Success case
 		res := step2("test")()
@@ -607,8 +607,8 @@ func TestLocalIOResultK(t *testing.T) {
 		}
 
 		// Compose the pipeline
-		step1 := LocalIOResultK[string, SimpleConfig, string](parseConfig)(useConfig)
-		step2 := LocalIOResultK[string, string, ConfigFile](readFile)(step1)
+		step1 := LocalIOResultK[string](parseConfig)(useConfig)
+		step2 := LocalIOResultK[string](readFile)(step1)
 
 		// Success case
 		res := step2(ConfigFile{Path: "app.json"})()
@@ -619,3 +619,453 @@ func TestLocalIOResultK(t *testing.T) {
 		assert.True(t, result.IsLeft(resErr))
 	})
 }
+
+func TestChainFirstIOResultK(t *testing.T) {
+	type Config struct {
+		logEnabled bool
+	}
+
+	t.Run("Success - preserves original value", func(t *testing.T) {
+		sideEffectRan := false
+
+		logValue := func(v int) IOResult[string] {
+			return func() Result[string] {
+				sideEffectRan = true
+				return result.Of(fmt.Sprintf("Logged: %d", v))
+			}
+		}
+
+		pipeline := F.Pipe1(
+			Of[Config](42),
+			ChainFirstIOResultK[Config](logValue),
+		)
+
+		res := pipeline(Config{logEnabled: true})()
+		assert.Equal(t, result.Of(42), res)
+		assert.True(t, sideEffectRan)
+	})
+
+	t.Run("Failure - side effect fails", func(t *testing.T) {
+		sideEffectError := errors.New("side effect failed")
+
+		failingSideEffect := func(v int) IOResult[string] {
+			return func() Result[string] {
+				return result.Left[string](sideEffectError)
+			}
+		}
+
+		pipeline := F.Pipe1(
+			Of[Config](42),
+			ChainFirstIOResultK[Config](failingSideEffect),
+		)
+
+		res := pipeline(Config{})()
+		assert.True(t, E.IsLeft(res))
+	})
+
+	t.Run("Failure - original computation fails", func(t *testing.T) {
+		originalError := errors.New("original failed")
+		sideEffectRan := false
+
+		sideEffect := func(v int) IOResult[string] {
+			return func() Result[string] {
+				sideEffectRan = true
+				return result.Of("logged")
+			}
+		}
+
+		pipeline := F.Pipe1(
+			Left[Config, int](originalError),
+			ChainFirstIOResultK[Config](sideEffect),
+		)
+
+		res := pipeline(Config{})()
+		assert.Equal(t, result.Left[int](originalError), res)
+		assert.False(t, sideEffectRan)
+	})
+}
+
+func TestTapIOResultK(t *testing.T) {
+	type Config struct{}
+
+	t.Run("Success - preserves original value", func(t *testing.T) {
+		tapped := false
+
+		tapFunc := func(v int) IOResult[string] {
+			return func() Result[string] {
+				tapped = true
+				return result.Of(fmt.Sprintf("Tapped: %d", v))
+			}
+		}
+
+		pipeline := F.Pipe1(
+			Of[Config](42),
+			TapIOResultK[Config](tapFunc),
+		)
+
+		res := pipeline(Config{})()
+		assert.Equal(t, result.Of(42), res)
+		assert.True(t, tapped)
+	})
+
+	t.Run("Validation use case", func(t *testing.T) {
+		validatePositive := func(v int) IOResult[bool] {
+			return func() Result[bool] {
+				if v > 0 {
+					return result.Of(true)
+				}
+				return result.Left[bool](errors.New("must be positive"))
+			}
+		}
+
+		pipeline := F.Pipe1(
+			Of[Config](42),
+			TapIOResultK[Config](validatePositive),
+		)
+
+		res := pipeline(Config{})()
+		assert.Equal(t, result.Of(42), res)
+	})
+
+	t.Run("Validation failure", func(t *testing.T) {
+		validatePositive := func(v int) IOResult[bool] {
+			return func() Result[bool] {
+				if v > 0 {
+					return result.Of(true)
+				}
+				return result.Left[bool](errors.New("must be positive"))
+			}
+		}
+
+		pipeline := F.Pipe1(
+			Of[Config](-5),
+			TapIOResultK[Config](validatePositive),
+		)
+
+		res := pipeline(Config{})()
+		assert.True(t, E.IsLeft(res))
+	})
+}
+
+func TestTap(t *testing.T) {
+	type Config struct{}
+
+	t.Run("Success - preserves original value", func(t *testing.T) {
+		tapped := false
+
+		tapFunc := func(v int) ReaderIOResult[Config, string] {
+			return func(cfg Config) IOResult[string] {
+				return func() Result[string] {
+					tapped = true
+					return result.Of(fmt.Sprintf("Tapped: %d", v))
+				}
+			}
+		}
+
+		pipeline := F.Pipe1(
+			Of[Config](42),
+			Tap(tapFunc),
+		)
+
+		res := pipeline(Config{})()
+		assert.Equal(t, result.Of(42), res)
+		assert.True(t, tapped)
+	})
+
+	t.Run("Tap is alias for ChainFirst", func(t *testing.T) {
+		sideEffect := func(v int) ReaderIOResult[Config, string] {
+			return func(cfg Config) IOResult[string] {
+				return func() Result[string] {
+					return result.Of(fmt.Sprintf("Value: %d", v))
+				}
+			}
+		}
+
+		pipelineWithTap := F.Pipe1(
+			Of[Config](42),
+			Tap(sideEffect),
+		)
+
+		pipelineWithChainFirst := F.Pipe1(
+			Of[Config](42),
+			ChainFirst(sideEffect),
+		)
+
+		resultTap := pipelineWithTap(Config{})()
+		resultChainFirst := pipelineWithChainFirst(Config{})()
+
+		assert.Equal(t, resultChainFirst, resultTap)
+	})
+}
+
+func TestMonadTap(t *testing.T) {
+	type Config struct{}
+
+	t.Run("Success - preserves original value", func(t *testing.T) {
+		tapped := false
+
+		tapFunc := func(v int) ReaderIOResult[Config, string] {
+			return func(cfg Config) IOResult[string] {
+				return func() Result[string] {
+					tapped = true
+					return result.Of("tapped")
+				}
+			}
+		}
+
+		res := MonadTap(Of[Config](42), tapFunc)(Config{})()
+		assert.Equal(t, result.Of(42), res)
+		assert.True(t, tapped)
+	})
+}
+
+func TestTapEitherK(t *testing.T) {
+	type Config struct{}
+
+	t.Run("Success - preserves original value", func(t *testing.T) {
+		tapped := false
+
+		tapFunc := func(v int) Result[string] {
+			tapped = true
+			return result.Of(fmt.Sprintf("Tapped: %d", v))
+		}
+
+		pipeline := F.Pipe1(
+			Of[Config](42),
+			TapEitherK[Config](tapFunc),
+		)
+
+		res := pipeline(Config{})()
+		assert.Equal(t, result.Of(42), res)
+		assert.True(t, tapped)
+	})
+
+	t.Run("Failure - tap fails", func(t *testing.T) {
+		tapError := errors.New("tap failed")
+
+		tapFunc := func(v int) Result[string] {
+			return result.Left[string](tapError)
+		}
+
+		pipeline := F.Pipe1(
+			Of[Config](42),
+			TapEitherK[Config](tapFunc),
+		)
+
+		res := pipeline(Config{})()
+		assert.True(t, E.IsLeft(res))
+	})
+}
+
+func TestTapResultK(t *testing.T) {
+	type Config struct{}
+
+	t.Run("Success - preserves original value", func(t *testing.T) {
+		tapped := false
+
+		tapFunc := func(v int) Result[string] {
+			tapped = true
+			return result.Of("tapped")
+		}
+
+		pipeline := F.Pipe1(
+			Of[Config](42),
+			TapResultK[Config](tapFunc),
+		)
+
+		res := pipeline(Config{})()
+		assert.Equal(t, result.Of(42), res)
+		assert.True(t, tapped)
+	})
+}
+
+func TestTapReaderK(t *testing.T) {
+	type Config struct {
+		multiplier int
+	}
+
+	t.Run("Success - preserves original value with context", func(t *testing.T) {
+		tapped := false
+
+		tapFunc := func(v int) R.Reader[Config, string] {
+			return func(cfg Config) string {
+				tapped = true
+				return fmt.Sprintf("Value: %d, Multiplier: %d", v, cfg.multiplier)
+			}
+		}
+
+		pipeline := F.Pipe1(
+			Of[Config](42),
+			TapReaderK(tapFunc),
+		)
+
+		res := pipeline(Config{multiplier: 2})()
+		assert.Equal(t, result.Of(42), res)
+		assert.True(t, tapped)
+	})
+}
+
+func TestTapIOK(t *testing.T) {
+	type Config struct{}
+
+	t.Run("Success - preserves original value", func(t *testing.T) {
+		tapped := false
+
+		tapFunc := func(v int) IO[string] {
+			return func() string {
+				tapped = true
+				return fmt.Sprintf("Tapped: %d", v)
+			}
+		}
+
+		pipeline := F.Pipe1(
+			Of[Config](42),
+			TapIOK[Config](tapFunc),
+		)
+
+		res := pipeline(Config{})()
+		assert.Equal(t, result.Of(42), res)
+		assert.True(t, tapped)
+	})
+}
+
+func TestRead(t *testing.T) {
+	type Config struct {
+		value int
+	}
+
+	t.Run("Success - provides environment", func(t *testing.T) {
+		computation := func(cfg Config) IOResult[int] {
+			return func() Result[int] {
+				return result.Of(cfg.value * 2)
+			}
+		}
+
+		res := Read[int](Config{value: 21})(computation)()
+		assert.Equal(t, result.Of(42), res)
+	})
+
+	t.Run("Failure - computation fails", func(t *testing.T) {
+		compError := errors.New("computation failed")
+
+		computation := func(cfg Config) IOResult[int] {
+			return func() Result[int] {
+				return result.Left[int](compError)
+			}
+		}
+
+		res := Read[int](Config{value: 21})(computation)()
+		assert.Equal(t, result.Left[int](compError), res)
+	})
+}
+
+func TestChainLeft(t *testing.T) {
+	type Config struct{}
+
+	t.Run("Right passes through unchanged", func(t *testing.T) {
+		pipeline := F.Pipe1(
+			Right[Config](42),
+			ChainLeft(func(err error) ReaderIOResult[Config, int] {
+				return Left[Config, int](errors.New("should not run"))
+			}),
+		)
+
+		res := pipeline(Config{})()
+		assert.Equal(t, result.Of(42), res)
+	})
+
+	t.Run("Left transforms error", func(t *testing.T) {
+		originalError := errors.New("original")
+		newError := errors.New("transformed")
+
+		pipeline := F.Pipe1(
+			Left[Config, int](originalError),
+			ChainLeft(func(err error) ReaderIOResult[Config, int] {
+				return Left[Config, int](newError)
+			}),
+		)
+
+		res := pipeline(Config{})()
+		assert.Equal(t, result.Left[int](newError), res)
+	})
+
+	t.Run("Left recovers to Right", func(t *testing.T) {
+		pipeline := F.Pipe1(
+			Left[Config, int](errors.New("error")),
+			ChainLeft(func(err error) ReaderIOResult[Config, int] {
+				return Right[Config](99)
+			}),
+		)
+
+		res := pipeline(Config{})()
+		assert.Equal(t, result.Of(99), res)
+	})
+}
+
+func TestTapLeft(t *testing.T) {
+	type Config struct{}
+
+	t.Run("Right does not call function", func(t *testing.T) {
+		tapped := false
+
+		pipeline := F.Pipe1(
+			Right[Config](42),
+			TapLeft[int](func(err error) ReaderIOResult[Config, string] {
+				return func(cfg Config) IOResult[string] {
+					return func() Result[string] {
+						tapped = true
+						return result.Of("logged")
+					}
+				}
+			}),
+		)
+
+		res := pipeline(Config{})()
+		assert.Equal(t, result.Of(42), res)
+		assert.False(t, tapped)
+	})
+
+	t.Run("Left calls function but preserves error", func(t *testing.T) {
+		tapped := false
+		originalError := errors.New("original error")
+
+		pipeline := F.Pipe1(
+			Left[Config, int](originalError),
+			TapLeft[int](func(err error) ReaderIOResult[Config, string] {
+				return func(cfg Config) IOResult[string] {
+					return func() Result[string] {
+						tapped = true
+						return result.Of("side effect done")
+					}
+				}
+			}),
+		)
+
+		res := pipeline(Config{})()
+		assert.Equal(t, result.Left[int](originalError), res)
+		assert.True(t, tapped)
+	})
+}
+
+func TestTapLeftIOK(t *testing.T) {
+	type Config struct{}
+
+	t.Run("Left calls IO function but preserves error", func(t *testing.T) {
+		tapped := false
+		originalError := errors.New("original error")
+
+		pipeline := F.Pipe1(
+			Left[Config, int](originalError),
+			TapLeftIOK[int, Config](func(err error) IO[string] {
+				return func() string {
+					tapped = true
+					return "logged error"
+				}
+			}),
+		)
+
+		res := pipeline(Config{})()
+		assert.Equal(t, result.Left[int](originalError), res)
+		assert.True(t, tapped)
+	})
+}

v2/readerreaderioeither/reader.go

@@ -38,51 +38,75 @@ import (
 	"github.com/IBM/fp-go/v2/readeroption"
 )
 
+// FromReaderOption converts a ReaderOption to a ReaderReaderIOEither.
+// If the ReaderOption is None, the provided function is called to produce the error.
+//
 //go:inline
 func FromReaderOption[R, C, A, E any](onNone Lazy[E]) Kleisli[R, C, E, ReaderOption[R, A], A] {
 	return reader.Map[R](RIOE.FromOption[C, A](onNone))
 }
 
+// FromReaderIOEither lifts a ReaderIOEither into a ReaderReaderIOEither context.
+//
 //go:inline
 func FromReaderIOEither[C, E, R, A any](ma ReaderIOEither[R, E, A]) ReaderReaderIOEither[R, C, E, A] {
 	return reader.MonadMap(ma, RIOE.FromIOEither[C])
 }
 
+// FromReaderIO lifts a ReaderIO into a ReaderReaderIOEither, placing the result in the Right side.
+//
 //go:inline
 func FromReaderIO[C, E, R, A any](ma ReaderIO[R, A]) ReaderReaderIOEither[R, C, E, A] {
 	return RightReaderIO[C, E](ma)
 }
 
+// RightReaderIO lifts a ReaderIO into a ReaderReaderIOEither, placing the result in the Right side.
+//
 //go:inline
 func RightReaderIO[C, E, R, A any](ma ReaderIO[R, A]) ReaderReaderIOEither[R, C, E, A] {
 	return reader.MonadMap(ma, RIOE.RightIO[C, E, A])
 }
 
+// LeftReaderIO lifts a ReaderIO into a ReaderReaderIOEither, placing the result in the Left (error) side.
+//
 //go:inline
 func LeftReaderIO[C, A, R, E any](me ReaderIO[R, E]) ReaderReaderIOEither[R, C, E, A] {
 	return reader.MonadMap(me, RIOE.LeftIO[C, A, E])
 }
 
+// MonadMap applies a function to the value inside a ReaderReaderIOEither context.
+// If the computation is successful (Right), the function is applied to the value.
+//
 //go:inline
 func MonadMap[R, C, E, A, B any](fa ReaderReaderIOEither[R, C, E, A], f func(A) B) ReaderReaderIOEither[R, C, E, B] {
 	return reader.MonadMap(fa, RIOE.Map[C, E](f))
 }
 
+// Map returns a function that applies a transformation to the success value.
+// This is the curried version of MonadMap.
+//
 //go:inline
 func Map[R, C, E, A, B any](f func(A) B) Operator[R, C, E, A, B] {
 	return reader.Map[R](RIOE.Map[C, E](f))
 }
 
+// MonadMapTo replaces the success value with a constant value.
+//
 //go:inline
 func MonadMapTo[R, C, E, A, B any](fa ReaderReaderIOEither[R, C, E, A], b B) ReaderReaderIOEither[R, C, E, B] {
 	return reader.MonadMap(fa, RIOE.MapTo[C, E, A](b))
 }
 
+// MapTo returns a function that replaces the success value with a constant.
+// This is the curried version of MonadMapTo.
+//
 //go:inline
 func MapTo[R, C, E, A, B any](b B) Operator[R, C, E, A, B] {
 	return reader.Map[R](RIOE.MapTo[C, E, A](b))
 }
 
+// MonadChain sequences two computations where the second depends on the result of the first.
+//
 //go:inline
 func MonadChain[R, C, E, A, B any](fa ReaderReaderIOEither[R, C, E, A], f Kleisli[R, C, E, A, B]) ReaderReaderIOEither[R, C, E, B] {
 	return readert.MonadChain(
@@ -92,6 +116,9 @@ func MonadChain[R, C, E, A, B any](fa ReaderReaderIOEither[R, C, E, A], f Kleisl
 	)
 }
 
+// MonadChainFirst sequences two computations but keeps the result of the first.
+// Useful for performing side effects while preserving the original value.
+//
 //go:inline
 func MonadChainFirst[R, C, E, A, B any](fa ReaderReaderIOEither[R, C, E, A], f Kleisli[R, C, E, A, B]) ReaderReaderIOEither[R, C, E, A] {
 	return chain.MonadChainFirst(
@@ -101,11 +128,15 @@ func MonadChainFirst[R, C, E, A, B any](fa ReaderReaderIOEither[R, C, E, A], f K
 		f)
 }
 
+// MonadTap is an alias for MonadChainFirst, executing a side effect while preserving the original value.
+//
 //go:inline
 func MonadTap[R, C, E, A, B any](fa ReaderReaderIOEither[R, C, E, A], f Kleisli[R, C, E, A, B]) ReaderReaderIOEither[R, C, E, A] {
 	return MonadChainFirst(fa, f)
 }
 
+// MonadChainEitherK chains a computation that returns an Either into a ReaderReaderIOEither.
+//
 //go:inline
 func MonadChainEitherK[R, C, E, A, B any](ma ReaderReaderIOEither[R, C, E, A], f either.Kleisli[E, A, B]) ReaderReaderIOEither[R, C, E, B] {
 	return fromeither.MonadChainEitherK(
@@ -116,6 +147,9 @@ func MonadChainEitherK[R, C, E, A, B any](ma ReaderReaderIOEither[R, C, E, A], f
 	)
 }
 
+// ChainEitherK returns a function that chains an Either-returning function into ReaderReaderIOEither.
+// This is the curried version of MonadChainEitherK.
+//
 //go:inline
 func ChainEitherK[R, C, E, A, B any](f either.Kleisli[E, A, B]) Operator[R, C, E, A, B] {
 	return fromeither.ChainEitherK(
@@ -125,6 +159,8 @@ func ChainEitherK[R, C, E, A, B any](f either.Kleisli[E, A, B]) Operator[R, C, E
 	)
 }
 
+// MonadChainFirstEitherK chains an Either-returning computation but keeps the original value.
+//
 //go:inline
 func MonadChainFirstEitherK[R, C, E, A, B any](ma ReaderReaderIOEither[R, C, E, A], f either.Kleisli[E, A, B]) ReaderReaderIOEither[R, C, E, A] {
 	return fromeither.MonadChainFirstEitherK(
@@ -136,11 +172,16 @@ func MonadChainFirstEitherK[R, C, E, A, B any](ma ReaderReaderIOEither[R, C, E,
 	)
 }
 
+// MonadTapEitherK is an alias for MonadChainFirstEitherK, executing an Either side effect while preserving the original value.
+//
 //go:inline
 func MonadTapEitherK[R, C, E, A, B any](ma ReaderReaderIOEither[R, C, E, A], f either.Kleisli[E, A, B]) ReaderReaderIOEither[R, C, E, A] {
 	return MonadChainFirstEitherK(ma, f)
 }
 
+// ChainFirstEitherK returns a function that chains an Either computation while preserving the original value.
+// This is the curried version of MonadChainFirstEitherK.
+//
 //go:inline
 func ChainFirstEitherK[R, C, E, A, B any](f either.Kleisli[E, A, B]) Operator[R, C, E, A, A] {
 	return fromeither.ChainFirstEitherK(
@@ -151,11 +192,15 @@ func ChainFirstEitherK[R, C, E, A, B any](f either.Kleisli[E, A, B]) Operator[R,
 	)
 }
 
+// TapEitherK is an alias for ChainFirstEitherK, executing an Either side effect while preserving the original value.
+//
 //go:inline
 func TapEitherK[R, C, E, A, B any](f either.Kleisli[E, A, B]) Operator[R, C, E, A, A] {
 	return ChainFirstEitherK[R, C](f)
 }
 
+// MonadChainReaderK chains a Reader-returning computation into a ReaderReaderIOEither.
+//
 //go:inline
 func MonadChainReaderK[C, E, R, A, B any](ma ReaderReaderIOEither[R, C, E, A], f reader.Kleisli[R, A, B]) ReaderReaderIOEither[R, C, E, B] {
 	return fromreader.MonadChainReaderK(
@@ -166,6 +211,9 @@ func MonadChainReaderK[C, E, R, A, B any](ma ReaderReaderIOEither[R, C, E, A], f
 	)
 }
 
+// ChainReaderK returns a function that chains a Reader-returning function into ReaderReaderIOEither.
+// This is the curried version of MonadChainReaderK.
+//
 //go:inline
 func ChainReaderK[C, E, R, A, B any](f reader.Kleisli[R, A, B]) Operator[R, C, E, A, B] {
 	return fromreader.ChainReaderK(
@@ -175,6 +223,8 @@ func ChainReaderK[C, E, R, A, B any](f reader.Kleisli[R, A, B]) Operator[R, C, E
 	)
 }
 
+// MonadChainFirstReaderK chains a Reader computation but keeps the original value.
+//
 //go:inline
 func MonadChainFirstReaderK[C, E, R, A, B any](ma ReaderReaderIOEither[R, C, E, A], f reader.Kleisli[R, A, B]) ReaderReaderIOEither[R, C, E, A] {
 	return fromreader.MonadChainFirstReaderK(
@@ -185,11 +235,16 @@ func MonadChainFirstReaderK[C, E, R, A, B any](ma ReaderReaderIOEither[R, C, E,
 	)
 }
 
+// MonadTapReaderK is an alias for MonadChainFirstReaderK, executing a Reader side effect while preserving the original value.
+//
 //go:inline
 func MonadTapReaderK[C, E, R, A, B any](ma ReaderReaderIOEither[R, C, E, A], f reader.Kleisli[R, A, B]) ReaderReaderIOEither[R, C, E, A] {
 	return MonadChainFirstReaderK(ma, f)
 }
 
+// ChainFirstReaderK returns a function that chains a Reader computation while preserving the original value.
+// This is the curried version of MonadChainFirstReaderK.
+//
 //go:inline
 func ChainFirstReaderK[C, E, R, A, B any](f reader.Kleisli[R, A, B]) Operator[R, C, E, A, A] {
 	return fromreader.ChainFirstReaderK(
@@ -199,11 +254,15 @@ func ChainFirstReaderK[C, E, R, A, B any](f reader.Kleisli[R, A, B]) Operator[R,
 	)
 }
 
+// TapReaderK is an alias for ChainFirstReaderK, executing a Reader side effect while preserving the original value.
+//
 //go:inline
 func TapReaderK[C, E, R, A, B any](f reader.Kleisli[R, A, B]) Operator[R, C, E, A, A] {
 	return ChainFirstReaderK[C, E](f)
 }
 
+// MonadChainReaderIOK chains a ReaderIO-returning computation into a ReaderReaderIOEither.
+//
 //go:inline
 func MonadChainReaderIOK[C, E, R, A, B any](ma ReaderReaderIOEither[R, C, E, A], f readerio.Kleisli[R, A, B]) ReaderReaderIOEither[R, C, E, B] {
 	return fromreader.MonadChainReaderK(
@@ -214,6 +273,9 @@ func MonadChainReaderIOK[C, E, R, A, B any](ma ReaderReaderIOEither[R, C, E, A],
 	)
 }
 
+// ChainReaderIOK returns a function that chains a ReaderIO-returning function into ReaderReaderIOEither.
+// This is the curried version of MonadChainReaderIOK.
+//
 //go:inline
 func ChainReaderIOK[C, E, R, A, B any](f readerio.Kleisli[R, A, B]) Operator[R, C, E, A, B] {
 	return fromreader.ChainReaderK(
@@ -223,6 +285,8 @@ func ChainReaderIOK[C, E, R, A, B any](f readerio.Kleisli[R, A, B]) Operator[R,
 	)
 }
 
+// MonadChainFirstReaderIOK chains a ReaderIO computation but keeps the original value.
+//
 //go:inline
 func MonadChainFirstReaderIOK[C, E, R, A, B any](ma ReaderReaderIOEither[R, C, E, A], f readerio.Kleisli[R, A, B]) ReaderReaderIOEither[R, C, E, A] {
 	return fromreader.MonadChainFirstReaderK(
@@ -233,11 +297,16 @@ func MonadChainFirstReaderIOK[C, E, R, A, B any](ma ReaderReaderIOEither[R, C, E
 	)
 }
 
+// MonadTapReaderIOK is an alias for MonadChainFirstReaderIOK, executing a ReaderIO side effect while preserving the original value.
+//
 //go:inline
 func MonadTapReaderIOK[C, E, R, A, B any](ma ReaderReaderIOEither[R, C, E, A], f readerio.Kleisli[R, A, B]) ReaderReaderIOEither[R, C, E, A] {
 	return MonadChainFirstReaderIOK(ma, f)
 }
 
+// ChainFirstReaderIOK returns a function that chains a ReaderIO computation while preserving the original value.
+// This is the curried version of MonadChainFirstReaderIOK.
+//
 //go:inline
 func ChainFirstReaderIOK[C, E, R, A, B any](f readerio.Kleisli[R, A, B]) Operator[R, C, E, A, A] {
 	return fromreader.ChainFirstReaderK(
@@ -247,11 +316,15 @@ func ChainFirstReaderIOK[C, E, R, A, B any](f readerio.Kleisli[R, A, B]) Operato
 	)
 }
 
+// TapReaderIOK is an alias for ChainFirstReaderIOK, executing a ReaderIO side effect while preserving the original value.
+//
 //go:inline
 func TapReaderIOK[C, E, R, A, B any](f readerio.Kleisli[R, A, B]) Operator[R, C, E, A, A] {
 	return ChainFirstReaderIOK[C, E](f)
 }
 
+// MonadChainReaderEitherK chains a ReaderEither-returning computation into a ReaderReaderIOEither.
+//
 //go:inline
 func MonadChainReaderEitherK[R, C, E, A, B any](ma ReaderReaderIOEither[R, C, E, A], f RE.Kleisli[R, E, A, B]) ReaderReaderIOEither[R, C, E, B] {
 	return fromreader.MonadChainReaderK(
@@ -262,6 +335,9 @@ func MonadChainReaderEitherK[R, C, E, A, B any](ma ReaderReaderIOEither[R, C, E,
 	)
 }
 
+// ChainReaderEitherK returns a function that chains a ReaderEither-returning function into ReaderReaderIOEither.
+// This is the curried version of MonadChainReaderEitherK.
+//
 //go:inline
 func ChainReaderEitherK[C, E, R, A, B any](f RE.Kleisli[R, E, A, B]) Operator[R, C, E, A, B] {
 	return fromreader.ChainReaderK(
@@ -271,6 +347,8 @@ func ChainReaderEitherK[C, E, R, A, B any](f RE.Kleisli[R, E, A, B]) Operator[R,
 	)
 }
 
+// ChainReaderIOEitherK returns a function that chains a ReaderIOEither-returning function into ReaderReaderIOEither.
+//
 //go:inline
 func ChainReaderIOEitherK[C, R, E, A, B any](f RIOE.Kleisli[R, E, A, B]) Operator[R, C, E, A, B] {
 	return fromreader.ChainReaderK(
@@ -280,6 +358,8 @@ func ChainReaderIOEitherK[C, R, E, A, B any](f RIOE.Kleisli[R, E, A, B]) Operato
 	)
 }
 
+// MonadChainFirstReaderEitherK chains a ReaderEither computation but keeps the original value.
+//
 //go:inline
 func MonadChainFirstReaderEitherK[R, C, E, A, B any](ma ReaderReaderIOEither[R, C, E, A], f RE.Kleisli[R, E, A, B]) ReaderReaderIOEither[R, C, E, A] {
 	return fromreader.MonadChainFirstReaderK(
@@ -290,11 +370,16 @@ func MonadChainFirstReaderEitherK[R, C, E, A, B any](ma ReaderReaderIOEither[R,
 	)
 }
 
+// MonadTapReaderEitherK is an alias for MonadChainFirstReaderEitherK, executing a ReaderEither side effect while preserving the original value.
+//
 //go:inline
 func MonadTapReaderEitherK[R, C, E, A, B any](ma ReaderReaderIOEither[R, C, E, A], f RE.Kleisli[R, E, A, B]) ReaderReaderIOEither[R, C, E, A] {
 	return MonadChainFirstReaderEitherK(ma, f)
 }
 
+// ChainFirstReaderEitherK returns a function that chains a ReaderEither computation while preserving the original value.
+// This is the curried version of MonadChainFirstReaderEitherK.
+//
 //go:inline
 func ChainFirstReaderEitherK[C, E, R, A, B any](f RE.Kleisli[R, E, A, B]) Operator[R, C, E, A, A] {
 	return fromreader.ChainFirstReaderK(
@@ -304,11 +389,15 @@ func ChainFirstReaderEitherK[C, E, R, A, B any](f RE.Kleisli[R, E, A, B]) Operat
 	)
 }
 
+// TapReaderEitherK is an alias for ChainFirstReaderEitherK, executing a ReaderEither side effect while preserving the original value.
+//
 //go:inline
 func TapReaderEitherK[C, E, R, A, B any](f RE.Kleisli[R, E, A, B]) Operator[R, C, E, A, A] {
 	return ChainFirstReaderEitherK[C](f)
 }
 
+// ChainReaderOptionK returns a function that chains a ReaderOption-returning function into ReaderReaderIOEither.
+// If the ReaderOption is None, the provided error function is called.
 func ChainReaderOptionK[R, C, A, B, E any](onNone Lazy[E]) func(readeroption.Kleisli[R, A, B]) Operator[R, C, E, A, B] {
 
 	fro := FromReaderOption[R, C, B](onNone)
@@ -323,6 +412,8 @@ func ChainReaderOptionK[R, C, A, B, E any](onNone Lazy[E]) func(readeroption.Kle
 	}
 }
 
+// ChainFirstReaderOptionK chains a ReaderOption computation while preserving the original value.
+// If the ReaderOption is None, the provided error function is called.
 func ChainFirstReaderOptionK[R, C, A, B, E any](onNone Lazy[E]) func(readeroption.Kleisli[R, A, B]) Operator[R, C, E, A, A] {
 	fro := FromReaderOption[R, C, B](onNone)
 	return func(f readeroption.Kleisli[R, A, B]) Operator[R, C, E, A, A] {
@@ -334,11 +425,15 @@ func ChainFirstReaderOptionK[R, C, A, B, E any](onNone Lazy[E]) func(readeroptio
 	}
 }
 
+// TapReaderOptionK is an alias for ChainFirstReaderOptionK, executing a ReaderOption side effect while preserving the original value.
+//
 //go:inline
 func TapReaderOptionK[R, C, A, B, E any](onNone Lazy[E]) func(readeroption.Kleisli[R, A, B]) Operator[R, C, E, A, A] {
 	return ChainFirstReaderOptionK[R, C, A, B](onNone)
 }
 
+// MonadChainIOEitherK chains an IOEither-returning computation into a ReaderReaderIOEither.
+//
 //go:inline
 func MonadChainIOEitherK[R, C, E, A, B any](ma ReaderReaderIOEither[R, C, E, A], f IOE.Kleisli[E, A, B]) ReaderReaderIOEither[R, C, E, B] {
 	return fromioeither.MonadChainIOEitherK(
@@ -349,6 +444,9 @@ func MonadChainIOEitherK[R, C, E, A, B any](ma ReaderReaderIOEither[R, C, E, A],
 	)
 }
 
+// ChainIOEitherK returns a function that chains an IOEither-returning function into ReaderReaderIOEither.
+// This is the curried version of MonadChainIOEitherK.
+//
 //go:inline
 func ChainIOEitherK[R, C, E, A, B any](f IOE.Kleisli[E, A, B]) Operator[R, C, E, A, B] {
 	return fromioeither.ChainIOEitherK(
@@ -358,6 +456,8 @@ func ChainIOEitherK[R, C, E, A, B any](f IOE.Kleisli[E, A, B]) Operator[R, C, E,
 	)
 }
 
+// MonadChainIOK chains an IO-returning computation into a ReaderReaderIOEither.
+//
 //go:inline
 func MonadChainIOK[R, C, E, A, B any](ma ReaderReaderIOEither[R, C, E, A], f io.Kleisli[A, B]) ReaderReaderIOEither[R, C, E, B] {
 	return fromio.MonadChainIOK(
@@ -368,6 +468,9 @@ func MonadChainIOK[R, C, E, A, B any](ma ReaderReaderIOEither[R, C, E, A], f io.
 	)
 }
 
+// ChainIOK returns a function that chains an IO-returning function into ReaderReaderIOEither.
+// This is the curried version of MonadChainIOK.
+//
 //go:inline
 func ChainIOK[R, C, E, A, B any](f io.Kleisli[A, B]) Operator[R, C, E, A, B] {
 	return fromio.ChainIOK(
@@ -377,6 +480,8 @@ func ChainIOK[R, C, E, A, B any](f io.Kleisli[A, B]) Operator[R, C, E, A, B] {
 	)
 }
 
+// MonadChainFirstIOK chains an IO computation but keeps the original value.
+//
 //go:inline
 func MonadChainFirstIOK[R, C, E, A, B any](ma ReaderReaderIOEither[R, C, E, A], f io.Kleisli[A, B]) ReaderReaderIOEither[R, C, E, A] {
 	return fromio.MonadChainFirstIOK(
@@ -388,11 +493,16 @@ func MonadChainFirstIOK[R, C, E, A, B any](ma ReaderReaderIOEither[R, C, E, A],
 	)
 }
 
+// MonadTapIOK is an alias for MonadChainFirstIOK, executing an IO side effect while preserving the original value.
+//
 //go:inline
 func MonadTapIOK[R, C, E, A, B any](ma ReaderReaderIOEither[R, C, E, A], f io.Kleisli[A, B]) ReaderReaderIOEither[R, C, E, A] {
 	return MonadChainFirstIOK(ma, f)
 }
 
+// ChainFirstIOK returns a function that chains an IO computation while preserving the original value.
+// This is the curried version of MonadChainFirstIOK.
+//
 //go:inline
 func ChainFirstIOK[R, C, E, A, B any](f io.Kleisli[A, B]) Operator[R, C, E, A, A] {
 	return fromio.ChainFirstIOK(
@@ -403,11 +513,16 @@ func ChainFirstIOK[R, C, E, A, B any](f io.Kleisli[A, B]) Operator[R, C, E, A, A
 	)
 }
 
+// TapIOK is an alias for ChainFirstIOK, executing an IO side effect while preserving the original value.
+//
 //go:inline
 func TapIOK[R, C, E, A, B any](f io.Kleisli[A, B]) Operator[R, C, E, A, A] {
 	return ChainFirstIOK[R, C, E](f)
 }
 
+// ChainOptionK returns a function that chains an Option-returning function into ReaderReaderIOEither.
+// If the Option is None, the provided error function is called.
+//
 //go:inline
 func ChainOptionK[R, C, A, B, E any](onNone Lazy[E]) func(option.Kleisli[A, B]) Operator[R, C, E, A, B] {
 	return fromeither.ChainOptionK(
@@ -417,6 +532,8 @@ func ChainOptionK[R, C, A, B, E any](onNone Lazy[E]) func(option.Kleisli[A, B])
 	)
 }
 
+// MonadAp applies a function wrapped in a context to a value wrapped in a context.
+//
 //go:inline
 func MonadAp[R, C, E, A, B any](fab ReaderReaderIOEither[R, C, E, func(A) B], fa ReaderReaderIOEither[R, C, E, A]) ReaderReaderIOEither[R, C, E, B] {
 	return readert.MonadAp[
@@ -429,6 +546,8 @@ func MonadAp[R, C, E, A, B any](fab ReaderReaderIOEither[R, C, E, func(A) B], fa
 	)
 }
 
+// MonadApSeq applies a function in a context to a value in a context, executing them sequentially.
+//
 //go:inline
 func MonadApSeq[R, C, E, A, B any](fab ReaderReaderIOEither[R, C, E, func(A) B], fa ReaderReaderIOEither[R, C, E, A]) ReaderReaderIOEither[R, C, E, B] {
 	return readert.MonadAp[
@@ -441,6 +560,8 @@ func MonadApSeq[R, C, E, A, B any](fab ReaderReaderIOEither[R, C, E, func(A) B],
 	)
 }
 
+// MonadApPar applies a function in a context to a value in a context, executing them in parallel.
+//
 //go:inline
 func MonadApPar[R, C, E, A, B any](fab ReaderReaderIOEither[R, C, E, func(A) B], fa ReaderReaderIOEither[R, C, E, A]) ReaderReaderIOEither[R, C, E, B] {
 	return readert.MonadAp[
@@ -453,6 +574,9 @@ func MonadApPar[R, C, E, A, B any](fab ReaderReaderIOEither[R, C, E, func(A) B],
 	)
 }
 
+// Ap returns a function that applies a function in a context to a value in a context.
+// This is the curried version of MonadAp.
+//
 //go:inline
 func Ap[B, R, C, E, A any](fa ReaderReaderIOEither[R, C, E, A]) Operator[R, C, E, func(A) B, B] {
 	return readert.Ap[
@@ -464,6 +588,9 @@ func Ap[B, R, C, E, A any](fa ReaderReaderIOEither[R, C, E, A]) Operator[R, C, E
 	)
 }
 
+// Chain returns a function that sequences computations where the second depends on the first.
+// This is the curried version of MonadChain.
+//
 //go:inline
 func Chain[R, C, E, A, B any](f Kleisli[R, C, E, A, B]) Operator[R, C, E, A, B] {
 	return readert.Chain[ReaderReaderIOEither[R, C, E, A]](
@@ -472,6 +599,9 @@ func Chain[R, C, E, A, B any](f Kleisli[R, C, E, A, B]) Operator[R, C, E, A, B]
 	)
 }
 
+// ChainFirst returns a function that sequences computations but keeps the first result.
+// This is the curried version of MonadChainFirst.
+//
 //go:inline
 func ChainFirst[R, C, E, A, B any](f Kleisli[R, C, E, A, B]) Operator[R, C, E, A, A] {
 	return chain.ChainFirst(
@@ -480,96 +610,137 @@ func ChainFirst[R, C, E, A, B any](f Kleisli[R, C, E, A, B]) Operator[R, C, E, A
 		f)
 }
 
+// Tap is an alias for ChainFirst, executing a side effect while preserving the original value.
+//
 //go:inline
 func Tap[R, C, E, A, B any](f Kleisli[R, C, E, A, B]) Operator[R, C, E, A, A] {
 	return ChainFirst(f)
 }
 
+// Right creates a successful ReaderReaderIOEither with the given value.
+//
 //go:inline
 func Right[R, C, E, A any](a A) ReaderReaderIOEither[R, C, E, A] {
 	return reader.Of[R](RIOE.Right[C, E](a))
 }
 
+// Left creates a failed ReaderReaderIOEither with the given error.
+//
 //go:inline
 func Left[R, C, A, E any](e E) ReaderReaderIOEither[R, C, E, A] {
 	return reader.Of[R](RIOE.Left[C, A](e))
 }
 
+// Of creates a successful ReaderReaderIOEither with the given value.
+// This is the pointed functor operation.
+//
 //go:inline
 func Of[R, C, E, A any](a A) ReaderReaderIOEither[R, C, E, A] {
 	return Right[R, C, E](a)
 }
 
+// Flatten removes one level of nesting from a nested ReaderReaderIOEither.
+//
 //go:inline
 func Flatten[R, C, E, A any](mma ReaderReaderIOEither[R, C, E, ReaderReaderIOEither[R, C, E, A]]) ReaderReaderIOEither[R, C, E, A] {
 	return MonadChain(mma, function.Identity[ReaderReaderIOEither[R, C, E, A]])
 }
 
+// FromEither lifts an Either into a ReaderReaderIOEither context.
+//
 //go:inline
 func FromEither[R, C, E, A any](t Either[E, A]) ReaderReaderIOEither[R, C, E, A] {
 	return reader.Of[R](RIOE.FromEither[C](t))
 }
 
+// RightReader lifts a Reader into a ReaderReaderIOEither, placing the result in the Right side.
+//
 //go:inline
 func RightReader[C, E, R, A any](ma Reader[R, A]) ReaderReaderIOEither[R, C, E, A] {
 	return reader.MonadMap(ma, RIOE.Right[C, E])
 }
 
+// LeftReader lifts a Reader into a ReaderReaderIOEither, placing the result in the Left (error) side.
+//
 //go:inline
 func LeftReader[C, A, R, E any](ma Reader[R, E]) ReaderReaderIOEither[R, C, E, A] {
 	return reader.MonadMap(ma, RIOE.Left[C, A])
 }
 
+// FromReader lifts a Reader into a ReaderReaderIOEither context.
+//
 //go:inline
 func FromReader[C, E, R, A any](ma Reader[R, A]) ReaderReaderIOEither[R, C, E, A] {
 	return RightReader[C, E](ma)
 }
 
+// RightIO lifts an IO into a ReaderReaderIOEither, placing the result in the Right side.
+//
 //go:inline
 func RightIO[R, C, E, A any](ma IO[A]) ReaderReaderIOEither[R, C, E, A] {
 	return reader.Of[R](RIOE.RightIO[C, E](ma))
 }
 
+// LeftIO lifts an IO into a ReaderReaderIOEither, placing the result in the Left (error) side.
+//
 //go:inline
 func LeftIO[R, C, A, E any](ma IO[E]) ReaderReaderIOEither[R, C, E, A] {
 	return reader.Of[R](RIOE.LeftIO[C, A](ma))
 }
 
+// FromIO lifts an IO into a ReaderReaderIOEither context.
+//
 //go:inline
 func FromIO[R, C, E, A any](ma IO[A]) ReaderReaderIOEither[R, C, E, A] {
 	return RightIO[R, C, E](ma)
 }
 
+// FromIOEither lifts an IOEither into a ReaderReaderIOEither context.
+//
 //go:inline
 func FromIOEither[R, C, E, A any](ma IOEither[E, A]) ReaderReaderIOEither[R, C, E, A] {
 	return reader.Of[R](RIOE.FromIOEither[C](ma))
 }
 
+// FromReaderEither lifts a ReaderEither into a ReaderReaderIOEither context.
+//
 //go:inline
 func FromReaderEither[R, C, E, A any](ma RE.ReaderEither[R, E, A]) ReaderReaderIOEither[R, C, E, A] {
 	return reader.MonadMap(ma, RIOE.FromEither[C])
 }
 
+// Ask returns a ReaderReaderIOEither that retrieves the outer context.
+//
 //go:inline
 func Ask[R, C, E any]() ReaderReaderIOEither[R, C, E, R] {
 	return fromreader.Ask(FromReader[C, E, R, R])()
 }
 
+// Asks returns a ReaderReaderIOEither that retrieves a value derived from the outer context.
+//
 //go:inline
 func Asks[C, E, R, A any](r Reader[R, A]) ReaderReaderIOEither[R, C, E, A] {
 	return fromreader.Asks(FromReader[C, E, R, A])(r)
 }
 
+// FromOption converts an Option to a ReaderReaderIOEither.
+// If the Option is None, the provided function is called to produce the error.
+//
 //go:inline
 func FromOption[R, C, A, E any](onNone Lazy[E]) func(Option[A]) ReaderReaderIOEither[R, C, E, A] {
 	return fromeither.FromOption(FromEither[R, C, E, A], onNone)
 }
 
+// FromPredicate creates a ReaderReaderIOEither from a predicate.
+// If the predicate returns false, the onFalse function is called to produce the error.
+//
 //go:inline
 func FromPredicate[R, C, E, A any](pred func(A) bool, onFalse func(A) E) func(A) ReaderReaderIOEither[R, C, E, A] {
 	return fromeither.FromPredicate(FromEither[R, C, E, A], pred, onFalse)
 }
 
+// MonadAlt tries the first computation, and if it fails, tries the second.
+//
 //go:inline
 func MonadAlt[R, C, E, A any](first ReaderReaderIOEither[R, C, E, A], second Lazy[ReaderReaderIOEither[R, C, E, A]]) ReaderReaderIOEither[R, C, E, A] {
 	return func(r R) ReaderIOEither[C, E, A] {
@@ -579,36 +750,53 @@ func MonadAlt[R, C, E, A any](first ReaderReaderIOEither[R, C, E, A], second Laz
 	}
 }
 
+// Alt returns a function that tries an alternative computation if the first fails.
+// This is the curried version of MonadAlt.
+//
 //go:inline
 func Alt[R, C, E, A any](second Lazy[ReaderReaderIOEither[R, C, E, A]]) Operator[R, C, E, A, A] {
 	return function.Bind2nd(MonadAlt, second)
 }
 
+// MonadFlap applies a value to a function wrapped in a context.
+//
 //go:inline
 func MonadFlap[R, C, E, B, A any](fab ReaderReaderIOEither[R, C, E, func(A) B], a A) ReaderReaderIOEither[R, C, E, B] {
 	return functor.MonadFlap(MonadMap[R, C, E, func(A) B, B], fab, a)
 }
 
+// Flap returns a function that applies a fixed value to a function in a context.
+// This is the curried version of MonadFlap.
+//
 //go:inline
 func Flap[R, C, E, B, A any](a A) Operator[R, C, E, func(A) B, B] {
 	return functor.Flap(Map[R, C, E, func(A) B, B], a)
 }
 
+// MonadMapLeft applies a function to the error value, leaving success unchanged.
+//
 //go:inline
 func MonadMapLeft[R, C, E1, E2, A any](fa ReaderReaderIOEither[R, C, E1, A], f func(E1) E2) ReaderReaderIOEither[R, C, E2, A] {
 	return reader.MonadMap(fa, RIOE.MapLeft[C, A](f))
 }
 
+// MapLeft returns a function that transforms the error channel.
+// This is the curried version of MonadMapLeft.
+//
 //go:inline
 func MapLeft[R, C, A, E1, E2 any](f func(E1) E2) func(ReaderReaderIOEither[R, C, E1, A]) ReaderReaderIOEither[R, C, E2, A] {
 	return reader.Map[R](RIOE.MapLeft[C, A](f))
 }
 
+// Read executes a ReaderReaderIOEither by providing a concrete outer environment value.
+//
 //go:inline
 func Read[C, E, A, R any](r R) func(ReaderReaderIOEither[R, C, E, A]) ReaderIOEither[C, E, A] {
 	return reader.Read[ReaderIOEither[C, E, A]](r)
 }
 
+// ReadIOEither executes a ReaderReaderIOEither by providing an outer environment obtained from an IOEither.
+//
 //go:inline
 func ReadIOEither[A, R, C, E any](rio IOEither[E, R]) func(ReaderReaderIOEither[R, C, E, A]) ReaderIOEither[C, E, A] {
 	return func(rri ReaderReaderIOEither[R, C, E, A]) ReaderIOEither[C, E, A] {
@@ -623,6 +811,8 @@ func ReadIOEither[A, R, C, E any](rio IOEither[E, R]) func(ReaderReaderIOEither[
 	}
 }
 
+// ReadIO executes a ReaderReaderIOEither by providing an outer environment obtained from an IO.
+//
 //go:inline
 func ReadIO[C, E, A, R any](rio IO[R]) func(ReaderReaderIOEither[R, C, E, A]) ReaderIOEither[C, E, A] {
 	return func(rri ReaderReaderIOEither[R, C, E, A]) ReaderIOEither[C, E, A] {
@@ -637,6 +827,8 @@ func ReadIO[C, E, A, R any](rio IO[R]) func(ReaderReaderIOEither[R, C, E, A]) Re
 	}
 }
 
+// MonadChainLeft chains a computation on the error channel, allowing error recovery or transformation.
+//
 //go:inline
 func MonadChainLeft[R, C, EA, EB, A any](fa ReaderReaderIOEither[R, C, EA, A], f Kleisli[R, C, EB, EA, A]) ReaderReaderIOEither[R, C, EB, A] {
 	return readert.MonadChain(
@@ -646,6 +838,9 @@ func MonadChainLeft[R, C, EA, EB, A any](fa ReaderReaderIOEither[R, C, EA, A], f
 	)
 }
 
+// ChainLeft returns a function that chains a computation on the error channel.
+// This is the curried version of MonadChainLeft.
+//
 //go:inline
 func ChainLeft[R, C, EA, EB, A any](f Kleisli[R, C, EB, EA, A]) func(ReaderReaderIOEither[R, C, EA, A]) ReaderReaderIOEither[R, C, EB, A] {
 	return readert.Chain[ReaderReaderIOEither[R, C, EA, A]](
@@ -654,16 +849,22 @@ func ChainLeft[R, C, EA, EB, A any](f Kleisli[R, C, EB, EA, A]) func(ReaderReade
 	)
 }
 
+// Delay creates an operation that passes in the value after some delay.
+//
 //go:inline
 func Delay[R, C, E, A any](delay time.Duration) Operator[R, C, E, A, A] {
 	return reader.Map[R](RIOE.Delay[C, E, A](delay))
 }
 
+// After creates an operation that passes after the given time.Time.
+//
 //go:inline
 func After[R, C, E, A any](timestamp time.Time) Operator[R, C, E, A, A] {
 	return reader.Map[R](RIOE.After[C, E, A](timestamp))
 }
 
+// Defer creates a ReaderReaderIOEither lazily via a generator function.
+// The generator is called each time the ReaderReaderIOEither is executed.
 func Defer[R, C, E, A any](fa Lazy[ReaderReaderIOEither[R, C, E, A]]) ReaderReaderIOEither[R, C, E, A] {
 	return func(r R) ReaderIOEither[C, E, A] {
 		return func(c C) RIOE.IOEither[E, A] {

v2/readerreaderioeither/reader_test.go

@@ -91,7 +91,7 @@ func TestMonadMapTo(t *testing.T) {
 func TestChain(t *testing.T) {
 	g := F.Pipe1(
 		Of[OuterConfig, InnerConfig, error](1),
-		Chain[OuterConfig, InnerConfig, error](func(v int) ReaderReaderIOEither[OuterConfig, InnerConfig, error, string] {
+		Chain(func(v int) ReaderReaderIOEither[OuterConfig, InnerConfig, error, string] {
 			return Of[OuterConfig, InnerConfig, error](fmt.Sprintf("%d", v))
 		}),
 	)
@@ -193,7 +193,7 @@ func TestFromEither(t *testing.T) {
 
 	t.Run("Left", func(t *testing.T) {
 		err := errors.New("test error")
-		result := FromEither[OuterConfig, InnerConfig, error, int](E.Left[int](err))
+		result := FromEither[OuterConfig, InnerConfig](E.Left[int](err))
 		assert.Equal(t, E.Left[int](err), result(OuterConfig{})(InnerConfig{})())
 	})
 }
@@ -239,7 +239,7 @@ func TestLeftIO(t *testing.T) {
 func TestFromIOEither(t *testing.T) {
 	t.Run("Right", func(t *testing.T) {
 		ioe := IOE.Right[error](42)
-		result := FromIOEither[OuterConfig, InnerConfig, error](ioe)
+		result := FromIOEither[OuterConfig, InnerConfig](ioe)
 		assert.Equal(t, E.Right[error](42), result(OuterConfig{})(InnerConfig{})())
 	})
 
@@ -344,7 +344,7 @@ func TestFromPredicate(t *testing.T) {
 	})
 
 	t.Run("Predicate false", func(t *testing.T) {
-		result := FromPredicate[OuterConfig, InnerConfig, error](isPositive, onFalse)(-5)
+		result := FromPredicate[OuterConfig, InnerConfig](isPositive, onFalse)(-5)
 		expected := E.Left[int](fmt.Errorf("not positive: -5"))
 		assert.Equal(t, expected, result(OuterConfig{})(InnerConfig{})())
 	})
@@ -391,7 +391,7 @@ func TestRead(t *testing.T) {
 func TestChainEitherK(t *testing.T) {
 	g := F.Pipe1(
 		Of[OuterConfig, InnerConfig, error](1),
-		ChainEitherK[OuterConfig, InnerConfig, error](func(v int) E.Either[error, string] {
+		ChainEitherK[OuterConfig, InnerConfig](func(v int) E.Either[error, string] {
 			return E.Right[error](fmt.Sprintf("%d", v))
 		}),
 	)

v2/samples/README.md

@@ -6,9 +6,62 @@ This folder is meant to contain examples that illustrate how to use the library.
 
 [![introduction to fp-go](presentation/cover.jpg)](https://www.youtube.com/watch?v=Jif3jL6DRdw "introduction to fp-go")
 
-### References
+## External Documentation References
 
-- [Ryan's Blog](https://rlee.dev/practical-guide-to-fp-ts-part-1) - practical introduction into FP concepts
-- [Investigate Functional Programming Concepts in Go](https://betterprogramming.pub/investigate-functional-programming-concepts-in-go-1dada09bc913) - discussion around FP concepts in golang
-- [Investigating the I/O Monad in Go](https://medium.com/better-programming/investigating-the-i-o-monad-in-go-3c0fabbb4b3d) - a closer look at I/O monads in golang
-- 
+### Official Documentation
+
+- [API Documentation](https://pkg.go.dev/github.com/IBM/fp-go/v2) - Complete API reference
+- [Go 1.24 Release Notes](https://tip.golang.org/doc/go1.24) - Information about generic type aliases
+- [Go Blog: Generating code](https://go.dev/blog/generate) - Using `go generate`
+- [Go Context Package](https://pkg.go.dev/context) - Standard library context documentation
+
+### Functional Programming Concepts
+
+#### Introductory Resources
+- [Ryan's Blog](https://rlee.dev/practical-guide-to-fp-ts-part-1) - Practical introduction into FP concepts
+- [Investigate Functional Programming Concepts in Go](https://betterprogramming.pub/investigate-functional-programming-concepts-in-go-1dada09bc913) - Discussion around FP concepts in golang
+- [Investigating the I/O Monad in Go](https://medium.com/better-programming/investigating-the-i-o-monad-in-go-3c0fabbb4b3d) - A closer look at I/O monads in golang
+- [Professor Frisby's Mostly Adequate Guide](https://github.com/MostlyAdequate/mostly-adequate-guide) - Comprehensive FP guide
+- [mostly-adequate-fp-ts](https://github.com/ChuckJonas/mostly-adequate-fp-ts/) - TypeScript companion to Frisby's guide
+
+#### Currying and Function Composition
+- [Mostly Adequate Guide - Ch. 4: Currying](https://mostly-adequate.gitbook.io/mostly-adequate-guide/ch04) - Excellent introduction with clear examples
+- [Curry and Function Composition](https://medium.com/javascript-scene/curry-and-function-composition-2c208d774983) by Eric Elliott
+- [Why Curry Helps](https://hughfdjackson.com/javascript/why-curry-helps/) - Practical benefits of currying
+
+### Haskell and Type Theory
+
+- [Haskell Wiki - Currying](https://wiki.haskell.org/Currying) - Comprehensive explanation of currying in Haskell
+- [Learn You a Haskell - Higher Order Functions](http://learnyouahaskell.com/higher-order-functions) - Introduction to currying and partial application
+- [Haskell's Prelude](https://hackage.haskell.org/package/base/docs/Prelude.html) - Standard library showing data-last convention
+- [Haskell Pair Type](https://hackage.haskell.org/package/TypeCompose-0.9.14/docs/Data-Pair.html) - Haskell definition of Pair
+- [Haskell Lens Library](https://hackage.haskell.org/package/lens) - Pioneering optics library
+
+### Optics
+
+- [Introduction to optics: lenses and prisms](https://medium.com/@gcanti/introduction-to-optics-lenses-and-prisms-3230e73bfcfe) by Giulio Canti - Excellent introduction to optics concepts
+- [Lenses in Functional Programming](https://www.schoolofhaskell.com/school/to-infinity-and-beyond/pick-of-the-week/a-little-lens-starter-tutorial) - Tutorial on lens fundamentals
+- [Profunctor Optics: The Categorical View](https://bartoszmilewski.com/2017/07/07/profunctor-optics-the-categorical-view/) by Bartosz Milewski - Deep dive into the theory
+- [Why Optics?](https://www.tweag.io/blog/2022-01-06-optics-vs-lenses/) - Discussion of benefits and use cases
+
+### Related Libraries
+
+- [fp-ts](https://github.com/gcanti/fp-ts) - TypeScript library that inspired fp-go
+- [fp-ts Documentation](https://gcanti.github.io/fp-ts/) - TypeScript library documentation
+- [fp-ts Issue #1238](https://github.com/gcanti/fp-ts/issues/1238) - Real-world examples of data-last refactoring
+- [urfave/cli/v3](https://github.com/urfave/cli) - Underlying CLI framework
+
+### Project Resources
+
+- [GitHub Repository](https://github.com/IBM/fp-go) - Source code and issues
+- [Coverage Status](https://coveralls.io/github/IBM/fp-go?branch=main) - Test coverage reports
+- [Go Report Card](https://goreportcard.com/report/github.com/IBM/fp-go/v2) - Code quality metrics
+- [Apache License 2.0](https://github.com/IBM/fp-go/blob/main/LICENSE) - Project license
+
+### Internal Documentation
+
+- [DESIGN.md](../DESIGN.md) - Design philosophy and patterns
+- [IDIOMATIC_COMPARISON.md](../IDIOMATIC_COMPARISON.md) - Performance comparison between standard and idiomatic packages
+- [Optics Overview](../optics/README.md) - Complete guide to lenses, prisms, and other optics
+- [CLI Package](../cli/README.md) - Command-line interface utilities
+- [ReaderResult Package](../idiomatic/context/readerresult/README.md) - Context-aware result handling

v2/semigroup/semigroup.go

@@ -123,3 +123,78 @@ func Last[A any]() Semigroup[A] {
 func ToMagma[A any](s Semigroup[A]) M.Magma[A] {
 	return s
 }
+
+// ConcatWith creates a curried version of the Concat operation with the left argument fixed first.
+// It returns a function that takes the left operand and returns another function that takes
+// the right operand and performs the concatenation.
+//
+// This is useful for partial application and function composition patterns.
+//
+// # Type Parameters
+//
+//   - A: The type of elements in the semigroup
+//
+// # Parameters
+//
+//   - s: The semigroup to use for concatenation
+//
+// # Returns
+//
+//   - func(A) func(A) A: A curried function that takes left then right operand
+//
+// # Example Usage
+//
+//	import N "github.com/IBM/fp-go/v2/number"
+//	sum := N.SemigroupSum[int]()
+//	concatWith := ConcatWith(sum)
+//	add5 := concatWith(5)
+//	result := add5(3)  // 5 + 3 = 8
+//
+// # See Also
+//
+//   - AppendTo: Similar but fixes the right argument first
+func ConcatWith[A any](s Semigroup[A]) func(A) func(A) A {
+	return func(l A) func(A) A {
+		return func(r A) A {
+			return s.Concat(l, r)
+		}
+	}
+}
+
+// AppendTo creates a curried version of the Concat operation with the right argument fixed first.
+// It returns a function that takes the right operand and returns another function that takes
+// the left operand and performs the concatenation.
+//
+// This is useful for partial application where you want to fix the second argument first,
+// which is common in append-style operations.
+//
+// # Type Parameters
+//
+//   - A: The type of elements in the semigroup
+//
+// # Parameters
+//
+//   - s: The semigroup to use for concatenation
+//
+// # Returns
+//
+//   - func(A) func(A) A: A curried function that takes right then left operand
+//
+// # Example Usage
+//
+//	import S "github.com/IBM/fp-go/v2/string"
+//	strConcat := S.Semigroup
+//	appendTo := AppendTo(strConcat)
+//	addSuffix := appendTo("!")
+//	result := addSuffix("Hello")  // "Hello" + "!" = "Hello!"
+//
+// # See Also
+//
+//   - ConcatWith: Similar but fixes the left argument first
+func AppendTo[A any](s Semigroup[A]) func(A) func(A) A {
+	return func(r A) func(A) A {
+		return func(l A) A {
+			return s.Concat(l, r)
+		}
+	}
+}

v2/semigroup/semigroup_test.go

@@ -444,3 +444,261 @@ func BenchmarkFunctionSemigroup(b *testing.B) {
 		combined("hello")
 	}
 }
+
+// Test ConcatWith function
+func TestConcatWith(t *testing.T) {
+	t.Run("with integer addition", func(t *testing.T) {
+		add := MakeSemigroup(func(a, b int) int { return a + b })
+		concatWith := ConcatWith(add)
+
+		// Fix left operand to 5
+		add5 := concatWith(5)
+		assert.Equal(t, 8, add5(3))   // 5 + 3 = 8
+		assert.Equal(t, 15, add5(10)) // 5 + 10 = 15
+		assert.Equal(t, 5, add5(0))   // 5 + 0 = 5
+	})
+
+	t.Run("with string concatenation", func(t *testing.T) {
+		concat := MakeSemigroup(func(a, b string) string { return a + b })
+		concatWith := ConcatWith(concat)
+
+		// Fix left operand to "Hello, "
+		greet := concatWith("Hello, ")
+		assert.Equal(t, "Hello, World", greet("World"))
+		assert.Equal(t, "Hello, Bob", greet("Bob"))
+		assert.Equal(t, "Hello, ", greet(""))
+	})
+
+	t.Run("with subtraction (non-commutative)", func(t *testing.T) {
+		sub := MakeSemigroup(func(a, b int) int { return a - b })
+		concatWith := ConcatWith(sub)
+
+		// Fix left operand to 10
+		subtract10 := concatWith(10)
+		assert.Equal(t, 7, subtract10(3))   // 10 - 3 = 7
+		assert.Equal(t, 5, subtract10(5))   // 10 - 5 = 5
+		assert.Equal(t, -5, subtract10(15)) // 10 - 15 = -5
+	})
+
+	t.Run("with First semigroup", func(t *testing.T) {
+		first := First[int]()
+		concatWith := ConcatWith(first)
+
+		// Fix left operand to 42
+		always42 := concatWith(42)
+		assert.Equal(t, 42, always42(1))
+		assert.Equal(t, 42, always42(100))
+		assert.Equal(t, 42, always42(0))
+	})
+
+	t.Run("with Last semigroup", func(t *testing.T) {
+		last := Last[string]()
+		concatWith := ConcatWith(last)
+
+		// Fix left operand to "first"
+		alwaysSecond := concatWith("first")
+		assert.Equal(t, "second", alwaysSecond("second"))
+		assert.Equal(t, "other", alwaysSecond("other"))
+		assert.Equal(t, "", alwaysSecond(""))
+	})
+
+	t.Run("currying behavior", func(t *testing.T) {
+		mul := MakeSemigroup(func(a, b int) int { return a * b })
+		concatWith := ConcatWith(mul)
+
+		// Create multiple partially applied functions
+		double := concatWith(2)
+		triple := concatWith(3)
+		quadruple := concatWith(4)
+
+		assert.Equal(t, 10, double(5))    // 2 * 5 = 10
+		assert.Equal(t, 15, triple(5))    // 3 * 5 = 15
+		assert.Equal(t, 20, quadruple(5)) // 4 * 5 = 20
+	})
+
+	t.Run("with complex types", func(t *testing.T) {
+		type Point struct {
+			X, Y int
+		}
+
+		pointAdd := MakeSemigroup(func(a, b Point) Point {
+			return Point{X: a.X + b.X, Y: a.Y + b.Y}
+		})
+		concatWith := ConcatWith(pointAdd)
+
+		// Fix left operand to origin offset
+		offset := concatWith(Point{X: 10, Y: 20})
+		assert.Equal(t, Point{X: 15, Y: 25}, offset(Point{X: 5, Y: 5}))
+		assert.Equal(t, Point{X: 10, Y: 20}, offset(Point{X: 0, Y: 0}))
+	})
+}
+
+// Test AppendTo function
+func TestAppendTo(t *testing.T) {
+	t.Run("with integer addition", func(t *testing.T) {
+		add := MakeSemigroup(func(a, b int) int { return a + b })
+		appendTo := AppendTo(add)
+
+		// Fix right operand to 5
+		addTo5 := appendTo(5)
+		assert.Equal(t, 8, addTo5(3))   // 3 + 5 = 8
+		assert.Equal(t, 15, addTo5(10)) // 10 + 5 = 15
+		assert.Equal(t, 5, addTo5(0))   // 0 + 5 = 5
+	})
+
+	t.Run("with string concatenation", func(t *testing.T) {
+		concat := MakeSemigroup(func(a, b string) string { return a + b })
+		appendTo := AppendTo(concat)
+
+		// Fix right operand to "!"
+		addExclamation := appendTo("!")
+		assert.Equal(t, "Hello!", addExclamation("Hello"))
+		assert.Equal(t, "World!", addExclamation("World"))
+		assert.Equal(t, "!", addExclamation(""))
+	})
+
+	t.Run("with subtraction (non-commutative)", func(t *testing.T) {
+		sub := MakeSemigroup(func(a, b int) int { return a - b })
+		appendTo := AppendTo(sub)
+
+		// Fix right operand to 3
+		subtract3 := appendTo(3)
+		assert.Equal(t, 7, subtract3(10))  // 10 - 3 = 7
+		assert.Equal(t, 2, subtract3(5))   // 5 - 3 = 2
+		assert.Equal(t, -3, subtract3(0))  // 0 - 3 = -3
+		assert.Equal(t, -8, subtract3(-5)) // -5 - 3 = -8
+	})
+
+	t.Run("with First semigroup", func(t *testing.T) {
+		first := First[string]()
+		appendTo := AppendTo(first)
+
+		// Fix right operand to "second"
+		alwaysFirst := appendTo("second")
+		assert.Equal(t, "first", alwaysFirst("first"))
+		assert.Equal(t, "other", alwaysFirst("other"))
+		assert.Equal(t, "", alwaysFirst(""))
+	})
+
+	t.Run("with Last semigroup", func(t *testing.T) {
+		last := Last[int]()
+		appendTo := AppendTo(last)
+
+		// Fix right operand to 42
+		always42 := appendTo(42)
+		assert.Equal(t, 42, always42(1))
+		assert.Equal(t, 42, always42(100))
+		assert.Equal(t, 42, always42(0))
+	})
+
+	t.Run("currying behavior", func(t *testing.T) {
+		mul := MakeSemigroup(func(a, b int) int { return a * b })
+		appendTo := AppendTo(mul)
+
+		// Create multiple partially applied functions
+		multiplyBy2 := appendTo(2)
+		multiplyBy3 := appendTo(3)
+		multiplyBy4 := appendTo(4)
+
+		assert.Equal(t, 10, multiplyBy2(5)) // 5 * 2 = 10
+		assert.Equal(t, 15, multiplyBy3(5)) // 5 * 3 = 15
+		assert.Equal(t, 20, multiplyBy4(5)) // 5 * 4 = 20
+	})
+
+	t.Run("with complex types", func(t *testing.T) {
+		type Point struct {
+			X, Y int
+		}
+
+		pointAdd := MakeSemigroup(func(a, b Point) Point {
+			return Point{X: a.X + b.X, Y: a.Y + b.Y}
+		})
+		appendTo := AppendTo(pointAdd)
+
+		// Fix right operand to offset
+		addOffset := appendTo(Point{X: 10, Y: 20})
+		assert.Equal(t, Point{X: 15, Y: 25}, addOffset(Point{X: 5, Y: 5}))
+		assert.Equal(t, Point{X: 10, Y: 20}, addOffset(Point{X: 0, Y: 0}))
+	})
+}
+
+// Test ConcatWith vs AppendTo difference
+func TestConcatWithVsAppendTo(t *testing.T) {
+	t.Run("demonstrates order difference with non-commutative operation", func(t *testing.T) {
+		sub := MakeSemigroup(func(a, b int) int { return a - b })
+
+		concatWith := ConcatWith(sub)
+		appendTo := AppendTo(sub)
+
+		// ConcatWith fixes left operand first
+		subtract10From := concatWith(10)      // 10 - x
+		assert.Equal(t, 7, subtract10From(3)) // 10 - 3 = 7
+
+		// AppendTo fixes right operand first
+		subtract3From := appendTo(3)          // x - 3
+		assert.Equal(t, 7, subtract3From(10)) // 10 - 3 = 7
+
+		// Same result but different partial application order
+		assert.Equal(t, subtract10From(3), subtract3From(10))
+	})
+
+	t.Run("demonstrates order difference with string concatenation", func(t *testing.T) {
+		concat := MakeSemigroup(func(a, b string) string { return a + b })
+
+		concatWith := ConcatWith(concat)
+		appendTo := AppendTo(concat)
+
+		// ConcatWith: prefix is fixed
+		addPrefix := concatWith("Hello, ")
+		assert.Equal(t, "Hello, World", addPrefix("World"))
+
+		// AppendTo: suffix is fixed
+		addSuffix := appendTo("!")
+		assert.Equal(t, "Hello!", addSuffix("Hello"))
+
+		// Different results due to different order
+		assert.NotEqual(t, addPrefix("test"), addSuffix("test"))
+	})
+}
+
+// Test composition with ConcatWith and AppendTo
+func TestConcatWithAppendToComposition(t *testing.T) {
+	t.Run("composing multiple operations", func(t *testing.T) {
+		add := MakeSemigroup(func(a, b int) int { return a + b })
+
+		// Create a pipeline: add 5, then add 3
+		concatWith := ConcatWith(add)
+		appendTo := AppendTo(add)
+
+		add5 := concatWith(5)
+		add3 := appendTo(3)
+
+		// Apply both operations
+		result := add3(add5(2)) // (2 + 5) + 3 = 10
+		assert.Equal(t, 10, result)
+	})
+}
+
+// Benchmark ConcatWith
+func BenchmarkConcatWith(b *testing.B) {
+	add := MakeSemigroup(func(a, b int) int { return a + b })
+	concatWith := ConcatWith(add)
+	add5 := concatWith(5)
+
+	b.ResetTimer()
+	for b.Loop() {
+		add5(3)
+	}
+}
+
+// Benchmark AppendTo
+func BenchmarkAppendTo(b *testing.B) {
+	add := MakeSemigroup(func(a, b int) int { return a + b })
+	appendTo := AppendTo(add)
+	addTo5 := appendTo(5)
+
+	b.ResetTimer()
+	for b.Loop() {
+		addTo5(3)
+	}
+}