fix: add template based logger

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

v2/IDIOMATIC_COMPARISON.md

@@ -314,7 +314,7 @@ if err != nil {
 
 ```go
 // Map transforms the success value
-double := result.Map(func(x int) int { return x * 2 })
+double := result.Map(N.Mul(2))
 result := double(result.Right[error](21))  // Right(42)
 
 // Chain sequences operations
@@ -330,7 +330,7 @@ validate := result.Chain(func(x int) result.Result[int] {
 
 ```go
 // Map transforms the success value
-double := result.Map(func(x int) int { return x * 2 })
+double := result.Map(N.Mul(2))
 value, err := double(21, nil)  // (42, nil)
 
 // Chain sequences operations

v2/README.md

@@ -205,7 +205,7 @@ The `Compose` function for endomorphisms now follows **mathematical function com
 ```go
 // Compose executed left-to-right
 double := N.Mul(2)
-increment := func(x int) int { return x + 1 }
+increment := N.Add(1)
 composed := Compose(double, increment)
 result := composed(5) // (5 * 2) + 1 = 11
 ```
@@ -214,7 +214,7 @@ result := composed(5) // (5 * 2) + 1 = 11
 ```go
 // Compose executes RIGHT-TO-LEFT (mathematical composition)
 double := N.Mul(2)
-increment := func(x int) int { return x + 1 }
+increment := N.Add(1)
 composed := Compose(double, increment)
 result := composed(5) // (5 + 1) * 2 = 12
 

v2/array/array_extended_test.go

@@ -35,7 +35,7 @@ func TestReplicate(t *testing.T) {
 
 func TestMonadMap(t *testing.T) {
 	src := []int{1, 2, 3}
-	result := MonadMap(src, func(x int) int { return x * 2 })
+	result := MonadMap(src, N.Mul(2))
 	assert.Equal(t, []int{2, 4, 6}, result)
 }
 
@@ -173,8 +173,8 @@ func TestChain(t *testing.T) {
 
 func TestMonadAp(t *testing.T) {
 	fns := []func(int) int{
-		func(x int) int { return x * 2 },
-		func(x int) int { return x + 10 },
+		N.Mul(2),
+		N.Add(10),
 	}
 	values := []int{1, 2}
 	result := MonadAp(fns, values)
@@ -268,7 +268,7 @@ func TestCopy(t *testing.T) {
 
 func TestClone(t *testing.T) {
 	src := []int{1, 2, 3}
-	cloner := Clone(func(x int) int { return x * 2 })
+	cloner := Clone(N.Mul(2))
 	result := cloner(src)
 	assert.Equal(t, []int{2, 4, 6}, result)
 }

v2/assert/assert.go

@@ -50,6 +50,7 @@ import (
 
 	"github.com/IBM/fp-go/v2/boolean"
 	"github.com/IBM/fp-go/v2/eq"
+	"github.com/IBM/fp-go/v2/option"
 	"github.com/IBM/fp-go/v2/reader"
 	"github.com/IBM/fp-go/v2/result"
 	"github.com/stretchr/testify/assert"
@@ -106,6 +107,13 @@ func RecordNotEmpty[K comparable, T any](mp map[K]T) Reader {
 	}
 }
 
+// StringNotEmpty checks if a string is not empty
+func StringNotEmpty(s string) Reader {
+	return func(t *testing.T) bool {
+		return assert.NotEmpty(t, s)
+	}
+}
+
 // ArrayLength tests if an array has the expected length
 func ArrayLength[T any](expected int) Kleisli[[]T] {
 	return func(actual []T) Reader {
@@ -266,3 +274,197 @@ func RunAll(testcases map[string]Reader) Reader {
 		return current
 	}
 }
+
+// Local transforms a Reader that works on type R1 into a Reader that works on type R2,
+// by providing a function that converts R2 to R1. This allows you to focus a test on a
+// specific property or subset of a larger data structure.
+//
+// This is particularly useful when you have an assertion that operates on a specific field
+// or property, and you want to apply it to a complete object. Instead of extracting the
+// property and then asserting on it, you can transform the assertion to work directly
+// on the whole object.
+//
+// Parameters:
+//   - f: A function that extracts or transforms R2 into R1
+//
+// Returns:
+//   - A function that transforms a Reader[R1, Reader] into a Reader[R2, Reader]
+//
+// Example:
+//
+//	type User struct {
+//	    Name string
+//	    Age  int
+//	}
+//
+//	// Create an assertion that checks if age is positive
+//	ageIsPositive := assert.That(func(age int) bool { return age > 0 })
+//
+//	// Focus this assertion on the Age field of User
+//	userAgeIsPositive := assert.Local(func(u User) int { return u.Age })(ageIsPositive)
+//
+//	// Now we can test the whole User object
+//	user := User{Name: "Alice", Age: 30}
+//	userAgeIsPositive(user)(t)
+//
+//go:inline
+func Local[R1, R2 any](f func(R2) R1) func(Kleisli[R1]) Kleisli[R2] {
+	return reader.Local[Reader](f)
+}
+
+// LocalL is similar to Local but uses a Lens to focus on a specific property.
+// A Lens is a functional programming construct that provides a composable way to
+// focus on a part of a data structure.
+//
+// This function is particularly useful when you want to focus a test on a specific
+// field of a struct using a lens, making the code more declarative and composable.
+// Lenses are often code-generated or predefined for common data structures.
+//
+// Parameters:
+//   - l: A Lens that focuses from type S to type T
+//
+// Returns:
+//   - A function that transforms a Reader[T, Reader] into a Reader[S, Reader]
+//
+// Example:
+//
+//	type Person struct {
+//	    Name  string
+//	    Email string
+//	}
+//
+//	// Assume we have a lens that focuses on the Email field
+//	var emailLens = lens.Prop[Person, string]("Email")
+//
+//	// Create an assertion for email format
+//	validEmail := assert.That(func(email string) bool {
+//	    return strings.Contains(email, "@")
+//	})
+//
+//	// Focus this assertion on the Email property using a lens
+//	validPersonEmail := assert.LocalL(emailLens)(validEmail)
+//
+//	// Test a Person object
+//	person := Person{Name: "Bob", Email: "bob@example.com"}
+//	validPersonEmail(person)(t)
+//
+//go:inline
+func LocalL[S, T any](l Lens[S, T]) func(Kleisli[T]) Kleisli[S] {
+	return reader.Local[Reader](l.Get)
+}
+
+// fromOptionalGetter is an internal helper that creates an assertion Reader from
+// an optional getter function. It asserts that the optional value is present (Some).
+func fromOptionalGetter[S, T any](getter func(S) option.Option[T], msgAndArgs ...any) Kleisli[S] {
+	return func(s S) Reader {
+		return func(t *testing.T) bool {
+			return assert.True(t, option.IsSome(getter(s)), msgAndArgs...)
+		}
+	}
+}
+
+// FromOptional creates an assertion that checks if an Optional can successfully extract a value.
+// An Optional is an optic that represents an optional reference to a subpart of a data structure.
+//
+// This function is useful when you have an Optional optic and want to assert that the optional
+// value is present (Some) rather than absent (None). The assertion passes if the Optional's
+// GetOption returns Some, and fails if it returns None.
+//
+// This enables property-focused testing where you verify that a particular optional field or
+// sub-structure exists and is accessible.
+//
+// Parameters:
+//   - opt: An Optional optic that focuses from type S to type T
+//
+// Returns:
+//   - A Reader that asserts the optional value is present when applied to a value of type S
+//
+// Example:
+//
+//	type Config struct {
+//	    Database *DatabaseConfig  // Optional field
+//	}
+//
+//	type DatabaseConfig struct {
+//	    Host string
+//	    Port int
+//	}
+//
+//	// Create an Optional that focuses on the Database field
+//	dbOptional := optional.MakeOptional(
+//	    func(c Config) option.Option[*DatabaseConfig] {
+//	        if c.Database != nil {
+//	            return option.Some(c.Database)
+//	        }
+//	        return option.None[*DatabaseConfig]()
+//	    },
+//	    func(c Config, db *DatabaseConfig) Config {
+//	        c.Database = db
+//	        return c
+//	    },
+//	)
+//
+//	// Assert that the database config is present
+//	hasDatabaseConfig := assert.FromOptional(dbOptional)
+//
+//	config := Config{Database: &DatabaseConfig{Host: "localhost", Port: 5432}}
+//	hasDatabaseConfig(config)(t)  // Passes
+//
+//	emptyConfig := Config{Database: nil}
+//	hasDatabaseConfig(emptyConfig)(t)  // Fails
+//
+//go:inline
+func FromOptional[S, T any](opt Optional[S, T]) reader.Reader[S, Reader] {
+	return fromOptionalGetter(opt.GetOption, "Optional: %s", opt)
+}
+
+// FromPrism creates an assertion that checks if a Prism can successfully extract a value.
+// A Prism is an optic used to select part of a sum type (tagged union or variant).
+//
+// This function is useful when you have a Prism optic and want to assert that a value
+// matches a specific variant of a sum type. The assertion passes if the Prism's GetOption
+// returns Some (meaning the value is of the expected variant), and fails if it returns None
+// (meaning the value is a different variant).
+//
+// This enables variant-focused testing where you verify that a value is of a particular
+// type or matches a specific condition within a sum type.
+//
+// Parameters:
+//   - p: A Prism optic that focuses from type S to type T
+//
+// Returns:
+//   - A Reader that asserts the prism successfully extracts when applied to a value of type S
+//
+// Example:
+//
+//	type Result interface{ isResult() }
+//	type Success struct{ Value int }
+//	type Failure struct{ Error string }
+//
+//	func (Success) isResult() {}
+//	func (Failure) isResult() {}
+//
+//	// Create a Prism that focuses on Success variant
+//	successPrism := prism.MakePrism(
+//	    func(r Result) option.Option[int] {
+//	        if s, ok := r.(Success); ok {
+//	            return option.Some(s.Value)
+//	        }
+//	        return option.None[int]()
+//	    },
+//	    func(v int) Result { return Success{Value: v} },
+//	)
+//
+//	// Assert that the result is a Success
+//	isSuccess := assert.FromPrism(successPrism)
+//
+//	result1 := Success{Value: 42}
+//	isSuccess(result1)(t)  // Passes
+//
+//	result2 := Failure{Error: "something went wrong"}
+//	isSuccess(result2)(t)  // Fails
+//
+//go:inline
+func FromPrism[S, T any](p Prism[S, T]) reader.Reader[S, Reader] {
+	return fromOptionalGetter(p.GetOption, "Prism: %s", p)
+}

v2/assert/assert_test.go

@@ -19,6 +19,8 @@ import (
 	"errors"
 	"testing"
 
+	"github.com/IBM/fp-go/v2/optics/prism"
+	"github.com/IBM/fp-go/v2/option"
 	"github.com/IBM/fp-go/v2/result"
 )
 
@@ -212,7 +214,7 @@ func TestError(t *testing.T) {
 
 func TestSuccess(t *testing.T) {
 	t.Run("should pass for successful result", func(t *testing.T) {
-		res := result.Of[int](42)
+		res := result.Of(42)
 		result := Success(res)(t)
 		if !result {
 			t.Error("Expected Success to pass for successful result")
@@ -240,7 +242,7 @@ func TestFailure(t *testing.T) {
 
 	t.Run("should fail for successful result", func(t *testing.T) {
 		mockT := &testing.T{}
-		res := result.Of[int](42)
+		res := result.Of(42)
 		result := Failure(res)(mockT)
 		if result {
 			t.Error("Expected Failure to fail for successful result")
@@ -445,41 +447,245 @@ func TestEq(t *testing.T) {
 	})
 }
 
-func TestIntegration(t *testing.T) {
-	t.Run("complex assertion composition", func(t *testing.T) {
-		type User struct {
-			Name  string
-			Age   int
-			Email string
+func TestLocal(t *testing.T) {
+	type User struct {
+		Name string
+		Age  int
+	}
+
+	t.Run("should focus assertion on a property", func(t *testing.T) {
+		// Create an assertion that checks if age is positive
+		ageIsPositive := That(func(age int) bool { return age > 0 })
+
+		// Focus this assertion on the Age field of User
+		userAgeIsPositive := Local(func(u User) int { return u.Age })(ageIsPositive)
+
+		// Test with a user who has a positive age
+		user := User{Name: "Alice", Age: 30}
+		result := userAgeIsPositive(user)(t)
+		if !result {
+			t.Error("Expected focused assertion to pass for positive age")
 		}
+	})
 
-		user := User{Name: "Alice", Age: 30, Email: "alice@example.com"}
+	t.Run("should fail when focused property doesn't match", func(t *testing.T) {
+		mockT := &testing.T{}
+		ageIsPositive := That(func(age int) bool { return age > 0 })
+		userAgeIsPositive := Local(func(u User) int { return u.Age })(ageIsPositive)
 
+		// Test with a user who has zero age
+		user := User{Name: "Bob", Age: 0}
+		result := userAgeIsPositive(user)(mockT)
+		if result {
+			t.Error("Expected focused assertion to fail for zero age")
+		}
+	})
+
+	t.Run("should compose with other assertions", func(t *testing.T) {
+		// Create multiple focused assertions
+		nameNotEmpty := Local(func(u User) string { return u.Name })(
+			That(func(name string) bool { return len(name) > 0 }),
+		)
+		ageInRange := Local(func(u User) int { return u.Age })(
+			That(func(age int) bool { return age >= 18 && age <= 100 }),
+		)
+
+		user := User{Name: "Charlie", Age: 25}
 		assertions := AllOf([]Reader{
-			Equal("Alice")(user.Name),
-			Equal(30)(user.Age),
-			That(func(s string) bool { return len(s) > 0 })(user.Email),
+			nameNotEmpty(user),
+			ageInRange(user),
 		})
 
 		result := assertions(t)
 		if !result {
-			t.Error("Expected complex assertion composition to pass")
+			t.Error("Expected composed focused assertions to pass")
 		}
 	})
 
-	t.Run("test suite with RunAll", func(t *testing.T) {
-		data := []int{1, 2, 3, 4, 5}
+	t.Run("should work with Equal assertion", func(t *testing.T) {
+		// Focus Equal assertion on Name field
+		nameIsAlice := Local(func(u User) string { return u.Name })(Equal("Alice"))
 
-		suite := RunAll(map[string]Reader{
-			"not_empty":     ArrayNotEmpty(data),
-			"correct_size":  ArrayLength[int](5)(data),
-			"contains_one":  ArrayContains(1)(data),
-			"contains_five": ArrayContains(5)(data),
-		})
-
-		result := suite(t)
+		user := User{Name: "Alice", Age: 30}
+		result := nameIsAlice(user)(t)
 		if !result {
-			t.Error("Expected test suite to pass")
+			t.Error("Expected focused Equal assertion to pass")
+		}
+	})
+}
+
+func TestLocalL(t *testing.T) {
+	// Note: LocalL requires lens package which provides lens operations.
+	// This test demonstrates the concept, but actual usage would require
+	// proper lens definitions.
+
+	t.Run("conceptual test for LocalL", func(t *testing.T) {
+		// LocalL is similar to Local but uses lenses for focusing.
+		// It would be used like:
+		// validEmail := That(func(email string) bool { return strings.Contains(email, "@") })
+		// validPersonEmail := LocalL(emailLens)(validEmail)
+		//
+		// The actual implementation would require lens definitions from the lens package.
+		// This test serves as documentation for the intended usage.
+	})
+}
+
+func TestFromOptional(t *testing.T) {
+	type DatabaseConfig struct {
+		Host string
+		Port int
+	}
+
+	type Config struct {
+		Database *DatabaseConfig
+	}
+
+	// Create an Optional that focuses on the Database field
+	dbOptional := Optional[Config, *DatabaseConfig]{
+		GetOption: func(c Config) option.Option[*DatabaseConfig] {
+			if c.Database != nil {
+				return option.Of(c.Database)
+			}
+			return option.None[*DatabaseConfig]()
+		},
+		Set: func(db *DatabaseConfig) func(Config) Config {
+			return func(c Config) Config {
+				c.Database = db
+				return c
+			}
+		},
+	}
+
+	t.Run("should pass when optional value is present", func(t *testing.T) {
+		config := Config{Database: &DatabaseConfig{Host: "localhost", Port: 5432}}
+		hasDatabaseConfig := FromOptional(dbOptional)
+		result := hasDatabaseConfig(config)(t)
+		if !result {
+			t.Error("Expected FromOptional to pass when optional value is present")
+		}
+	})
+
+	t.Run("should fail when optional value is absent", func(t *testing.T) {
+		mockT := &testing.T{}
+		emptyConfig := Config{Database: nil}
+		hasDatabaseConfig := FromOptional(dbOptional)
+		result := hasDatabaseConfig(emptyConfig)(mockT)
+		if result {
+			t.Error("Expected FromOptional to fail when optional value is absent")
+		}
+	})
+
+	t.Run("should work with nested optionals", func(t *testing.T) {
+		type AdvancedSettings struct {
+			Cache bool
+		}
+
+		type Settings struct {
+			Advanced *AdvancedSettings
+		}
+
+		advancedOptional := Optional[Settings, *AdvancedSettings]{
+			GetOption: func(s Settings) option.Option[*AdvancedSettings] {
+				if s.Advanced != nil {
+					return option.Of(s.Advanced)
+				}
+				return option.None[*AdvancedSettings]()
+			},
+			Set: func(adv *AdvancedSettings) func(Settings) Settings {
+				return func(s Settings) Settings {
+					s.Advanced = adv
+					return s
+				}
+			},
+		}
+
+		settings := Settings{Advanced: &AdvancedSettings{Cache: true}}
+		hasAdvanced := FromOptional(advancedOptional)
+		result := hasAdvanced(settings)(t)
+		if !result {
+			t.Error("Expected FromOptional to pass for nested optional")
+		}
+	})
+}
+
+// Helper types for Prism testing
+type PrismTestResult interface {
+	isPrismTestResult()
+}
+
+type PrismTestSuccess struct {
+	Value int
+}
+
+type PrismTestFailure struct {
+	Error string
+}
+
+func (PrismTestSuccess) isPrismTestResult() {}
+func (PrismTestFailure) isPrismTestResult() {}
+
+func TestFromPrism(t *testing.T) {
+	// Create a Prism that focuses on Success variant using prism.MakePrism
+	successPrism := prism.MakePrism(
+		func(r PrismTestResult) option.Option[int] {
+			if s, ok := r.(PrismTestSuccess); ok {
+				return option.Of(s.Value)
+			}
+			return option.None[int]()
+		},
+		func(v int) PrismTestResult {
+			return PrismTestSuccess{Value: v}
+		},
+	)
+
+	// Create a Prism that focuses on Failure variant
+	failurePrism := prism.MakePrism(
+		func(r PrismTestResult) option.Option[string] {
+			if f, ok := r.(PrismTestFailure); ok {
+				return option.Of(f.Error)
+			}
+			return option.None[string]()
+		},
+		func(err string) PrismTestResult {
+			return PrismTestFailure{Error: err}
+		},
+	)
+
+	t.Run("should pass when prism successfully extracts", func(t *testing.T) {
+		result := PrismTestSuccess{Value: 42}
+		isSuccess := FromPrism(successPrism)
+		testResult := isSuccess(result)(t)
+		if !testResult {
+			t.Error("Expected FromPrism to pass when prism extracts successfully")
+		}
+	})
+
+	t.Run("should fail when prism cannot extract", func(t *testing.T) {
+		mockT := &testing.T{}
+		result := PrismTestFailure{Error: "something went wrong"}
+		isSuccess := FromPrism(successPrism)
+		testResult := isSuccess(result)(mockT)
+		if testResult {
+			t.Error("Expected FromPrism to fail when prism cannot extract")
+		}
+	})
+
+	t.Run("should work with failure prism", func(t *testing.T) {
+		result := PrismTestFailure{Error: "test error"}
+		isFailure := FromPrism(failurePrism)
+		testResult := isFailure(result)(t)
+		if !testResult {
+			t.Error("Expected FromPrism to pass for failure prism on failure result")
+		}
+	})
+
+	t.Run("should fail with failure prism on success result", func(t *testing.T) {
+		mockT := &testing.T{}
+		result := PrismTestSuccess{Value: 100}
+		isFailure := FromPrism(failurePrism)
+		testResult := isFailure(result)(mockT)
+		if testResult {
+			t.Error("Expected FromPrism to fail for failure prism on success result")
 		}
 	})
 }

v2/assert/types.go

@@ -3,14 +3,20 @@ package assert
 import (
 	"testing"
 
+	"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/predicate"
 	"github.com/IBM/fp-go/v2/reader"
 	"github.com/IBM/fp-go/v2/result"
 )
 
 type (
-	Result[T any]    = result.Result[T]
-	Reader           = reader.Reader[*testing.T, bool]
-	Kleisli[T any]   = reader.Reader[T, Reader]
-	Predicate[T any] = predicate.Predicate[T]
+	Result[T any]      = result.Result[T]
+	Reader             = reader.Reader[*testing.T, bool]
+	Kleisli[T any]     = reader.Reader[T, Reader]
+	Predicate[T any]   = predicate.Predicate[T]
+	Lens[S, T any]     = lens.Lens[S, T]
+	Optional[S, T any] = optional.Optional[S, T]
+	Prism[S, T any]    = prism.Prism[S, T]
 )

v2/builder/prism.go

@@ -8,5 +8,5 @@ import (
 
 // BuilderPrism createa a [Prism] that converts between a builder and its type
 func BuilderPrism[T any, B Builder[T]](creator func(T) B) Prism[B, T] {
-	return prism.MakePrism(F.Flow2(B.Build, result.ToOption[T]), creator)
+	return prism.MakePrismWithName(F.Flow2(B.Build, result.ToOption[T]), creator, "BuilderPrism")
 }

v2/context/statereaderioresult/resource_test.go

@@ -27,9 +27,9 @@ import (
 
 // resourceState tracks the lifecycle of resources for testing
 type resourceState struct {
-	resourcesCreated int
+	resourcesCreated  int
 	resourcesReleased int
-	lastError        error
+	lastError         error
 }
 
 // mockResource represents a test resource

v2/context/statereaderioresult/state.go

@@ -68,7 +68,7 @@ func Of[S, A any](a A) StateReaderIOResult[S, A] {
 //
 //	result := statereaderioresult.MonadMap(
 //	    statereaderioresult.Of[AppState](21),
-//	    func(x int) int { return x * 2 },
+//	    N.Mul(2),
 //	) // Result contains 42
 func MonadMap[S, A, B any](fa StateReaderIOResult[S, A], f func(A) B) StateReaderIOResult[S, B] {
 	return statet.MonadMap[StateReaderIOResult[S, A], StateReaderIOResult[S, B]](
@@ -83,7 +83,7 @@ func MonadMap[S, A, B any](fa StateReaderIOResult[S, A], f func(A) B) StateReade
 //
 // Example:
 //
-//	double := statereaderioresult.Map[AppState](func(x int) int { return x * 2 })
+//	double := statereaderioresult.Map[AppState](N.Mul(2))
 //	result := function.Pipe1(statereaderioresult.Of[AppState](21), double)
 func Map[S, A, B any](f func(A) B) Operator[S, A, B] {
 	return statet.Map[StateReaderIOResult[S, A], StateReaderIOResult[S, B]](
@@ -135,7 +135,7 @@ func Chain[S, A, B any](f Kleisli[S, A, B]) Operator[S, A, B] {
 //
 // Example:
 //
-//	fab := statereaderioresult.Of[AppState](func(x int) int { return x * 2 })
+//	fab := statereaderioresult.Of[AppState](N.Mul(2))
 //	fa := statereaderioresult.Of[AppState](21)
 //	result := statereaderioresult.MonadAp(fab, fa) // Result contains 42
 func MonadAp[B, S, A any](fab StateReaderIOResult[S, func(A) B], fa StateReaderIOResult[S, A]) StateReaderIOResult[S, B] {

v2/context/statereaderioresult/statereaderioresult_test.go

@@ -215,7 +215,7 @@ func TestFromState(t *testing.T) {
 
 	assert.True(t, RES.IsRight(res))
 	RES.Map(func(p P.Pair[testState, int]) P.Pair[testState, int] {
-		assert.Equal(t, 11, P.Tail(p)) // Incremented value
+		assert.Equal(t, 11, P.Tail(p))         // Incremented value
 		assert.Equal(t, 11, P.Head(p).counter) // State updated
 		return p
 	})(res)
@@ -473,7 +473,7 @@ func TestStatefulComputation(t *testing.T) {
 	res := result(initialState)(ctx)()
 	assert.True(t, RES.IsRight(res))
 	RES.Map(func(p P.Pair[testState, int]) P.Pair[testState, int] {
-		assert.Equal(t, 3, P.Tail(p)) // Last incremented value
+		assert.Equal(t, 3, P.Tail(p))         // Last incremented value
 		assert.Equal(t, 3, P.Head(p).counter) // State updated three times
 		return p
 	})(res)

v2/context/statereaderioresult/testing/laws.go

@@ -19,12 +19,12 @@ import (
 	"context"
 	"testing"
 
+	RIORES "github.com/IBM/fp-go/v2/context/readerioresult"
+	ST "github.com/IBM/fp-go/v2/context/statereaderioresult"
 	EQ "github.com/IBM/fp-go/v2/eq"
 	L "github.com/IBM/fp-go/v2/internal/monad/testing"
 	P "github.com/IBM/fp-go/v2/pair"
 	RES "github.com/IBM/fp-go/v2/result"
-	RIORES "github.com/IBM/fp-go/v2/context/readerioresult"
-	ST "github.com/IBM/fp-go/v2/context/statereaderioresult"
 )
 
 // AssertLaws asserts the monad laws for the StateReaderIOResult monad

v2/either/monad.go

@@ -95,11 +95,11 @@ func (o *eitherMonad[E, A, B]) Chain(f Kleisli[E, A, B]) Operator[E, A, B] {
 //	m := either.Monad[error, int, int]()
 //
 //	// Map transforms the value
-//	value := m.Map(func(x int) int { return x * 2 })(either.Right[error](21))
+//	value := m.Map(N.Mul(2))(either.Right[error](21))
 //	// value is Right(42)
 //
 //	// Ap applies wrapped functions (also fails fast)
-//	fn := either.Right[error](func(x int) int { return x + 1 })
+//	fn := either.Right[error](N.Add(1))
 //	result := m.Ap(value)(fn)
 //	// result is Right(43)
 //

v2/endomorphism/builder.go

@@ -0,0 +1,406 @@
+// 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 endomorphism
+
+import (
+	"github.com/IBM/fp-go/v2/function"
+	A "github.com/IBM/fp-go/v2/internal/array"
+)
+
+// Build applies an endomorphism to the zero value of type A, effectively using
+// the endomorphism as a builder pattern.
+//
+// # Endomorphism as Builder Pattern
+//
+// An endomorphism (a function from type A to type A) can be viewed as a builder pattern
+// because it transforms a value of a type into another value of the same type. When you
+// compose multiple endomorphisms together, you create a pipeline of transformations that
+// build up a final value step by step.
+//
+// The Build function starts with the zero value of type A and applies the endomorphism
+// to it, making it particularly useful for building complex values from scratch using
+// a functional composition of transformations.
+//
+// # Builder Pattern Characteristics
+//
+// Traditional builder patterns have these characteristics:
+//  1. Start with an initial (often empty) state
+//  2. Apply a series of transformations/configurations
+//  3. Return the final built object
+//
+// Endomorphisms provide the same pattern functionally:
+//  1. Start with zero value: var a A
+//  2. Apply composed endomorphisms: e(a)
+//  3. Return the transformed value
+//
+// # Type Parameters
+//
+//   - A: The type being built/transformed
+//
+// # Parameters
+//
+//   - e: An endomorphism (or composition of endomorphisms) that transforms type A
+//
+// # Returns
+//
+//	The result of applying the endomorphism to the zero value of type A
+//
+// # Example - Building a Configuration Object
+//
+//	type Config struct {
+//	    Host     string
+//	    Port     int
+//	    Timeout  time.Duration
+//	    Debug    bool
+//	}
+//
+//	// Define builder functions as endomorphisms
+//	withHost := func(host string) Endomorphism[Config] {
+//	    return func(c Config) Config {
+//	        c.Host = host
+//	        return c
+//	    }
+//	}
+//
+//	withPort := func(port int) Endomorphism[Config] {
+//	    return func(c Config) Config {
+//	        c.Port = port
+//	        return c
+//	    }
+//	}
+//
+//	withTimeout := func(d time.Duration) Endomorphism[Config] {
+//	    return func(c Config) Config {
+//	        c.Timeout = d
+//	        return c
+//	    }
+//	}
+//
+//	withDebug := func(debug bool) Endomorphism[Config] {
+//	    return func(c Config) Config {
+//	        c.Debug = debug
+//	        return c
+//	    }
+//	}
+//
+//	// Compose builders using monoid operations
+//	import M "github.com/IBM/fp-go/v2/monoid"
+//
+//	configBuilder := M.ConcatAll(Monoid[Config]())(
+//	    withHost("localhost"),
+//	    withPort(8080),
+//	    withTimeout(30 * time.Second),
+//	    withDebug(true),
+//	)
+//
+//	// Build the final configuration
+//	config := Build(configBuilder)
+//	// Result: Config{Host: "localhost", Port: 8080, Timeout: 30s, Debug: true}
+//
+// # Example - Building a String with Transformations
+//
+//	import (
+//	    "strings"
+//	    M "github.com/IBM/fp-go/v2/monoid"
+//	)
+//
+//	// Define string transformation endomorphisms
+//	appendHello := func(s string) string { return s + "Hello" }
+//	appendSpace := func(s string) string { return s + " " }
+//	appendWorld := func(s string) string { return s + "World" }
+//	toUpper := strings.ToUpper
+//
+//	// Compose transformations
+//	stringBuilder := M.ConcatAll(Monoid[string]())(
+//	    appendHello,
+//	    appendSpace,
+//	    appendWorld,
+//	    toUpper,
+//	)
+//
+//	// Build the final string from empty string
+//	result := Build(stringBuilder)
+//	// Result: "HELLO WORLD"
+//
+// # Example - Building a Slice with Operations
+//
+//	type IntSlice []int
+//
+//	appendValue := func(v int) Endomorphism[IntSlice] {
+//	    return func(s IntSlice) IntSlice {
+//	        return append(s, v)
+//	    }
+//	}
+//
+//	sortSlice := func(s IntSlice) IntSlice {
+//	    sorted := make(IntSlice, len(s))
+//	    copy(sorted, s)
+//	    sort.Ints(sorted)
+//	    return sorted
+//	}
+//
+//	// Build a sorted slice
+//	sliceBuilder := M.ConcatAll(Monoid[IntSlice]())(
+//	    appendValue(5),
+//	    appendValue(2),
+//	    appendValue(8),
+//	    appendValue(1),
+//	    sortSlice,
+//	)
+//
+//	result := Build(sliceBuilder)
+//	// Result: IntSlice{1, 2, 5, 8}
+//
+// # Advantages of Endomorphism Builder Pattern
+//
+//  1. **Composability**: Builders can be composed using monoid operations
+//  2. **Immutability**: Each transformation returns a new value (if implemented immutably)
+//  3. **Type Safety**: The type system ensures all transformations work on the same type
+//  4. **Reusability**: Individual builder functions can be reused and combined differently
+//  5. **Testability**: Each transformation can be tested independently
+//  6. **Declarative**: The composition clearly expresses the building process
+//
+// # Comparison with Traditional Builder Pattern
+//
+// Traditional OOP Builder:
+//
+//	config := NewConfigBuilder().
+//	    WithHost("localhost").
+//	    WithPort(8080).
+//	    WithTimeout(30 * time.Second).
+//	    Build()
+//
+// Endomorphism Builder:
+//
+//	config := Build(M.ConcatAll(Monoid[Config]())(
+//	    withHost("localhost"),
+//	    withPort(8080),
+//	    withTimeout(30 * time.Second),
+//	))
+//
+// Both achieve the same goal, but the endomorphism approach:
+//   - Uses pure functions instead of methods
+//   - Leverages algebraic properties (monoid) for composition
+//   - Allows for more flexible composition patterns
+//   - Integrates naturally with other functional programming constructs
+func Build[A any](e Endomorphism[A]) A {
+	var a A
+	return e(a)
+}
+
+// ConcatAll combines multiple endomorphisms into a single endomorphism using composition.
+//
+// This function takes a slice of endomorphisms and combines them using the monoid's
+// concat operation (which is composition). The resulting endomorphism, when applied,
+// will execute all the input endomorphisms in RIGHT-TO-LEFT order (mathematical composition order).
+//
+// IMPORTANT: Execution order is RIGHT-TO-LEFT:
+//   - ConcatAll([]Endomorphism{f, g, h}) creates an endomorphism that applies h, then g, then f
+//   - This is equivalent to f ∘ g ∘ h in mathematical notation
+//   - The last endomorphism in the slice is applied first
+//
+// If the slice is empty, returns the identity endomorphism.
+//
+// # Type Parameters
+//
+//   - T: The type that the endomorphisms operate on
+//
+// # Parameters
+//
+//   - es: A slice of endomorphisms to combine
+//
+// # Returns
+//
+//	A single endomorphism that represents the composition of all input endomorphisms
+//
+// # Example - Basic Composition
+//
+//	double := N.Mul(2)
+//	increment := N.Add(1)
+//	square := func(x int) int { return x * x }
+//
+//	// Combine endomorphisms (RIGHT-TO-LEFT execution)
+//	combined := ConcatAll([]Endomorphism[int]{double, increment, square})
+//	result := combined(5)
+//	// Execution: square(5) = 25, increment(25) = 26, double(26) = 52
+//	// Result: 52
+//
+// # Example - Building with ConcatAll
+//
+//	type Config struct {
+//	    Host string
+//	    Port int
+//	}
+//
+//	withHost := func(host string) Endomorphism[Config] {
+//	    return func(c Config) Config {
+//	        c.Host = host
+//	        return c
+//	    }
+//	}
+//
+//	withPort := func(port int) Endomorphism[Config] {
+//	    return func(c Config) Config {
+//	        c.Port = port
+//	        return c
+//	    }
+//	}
+//
+//	// Combine configuration builders
+//	configBuilder := ConcatAll([]Endomorphism[Config]{
+//	    withHost("localhost"),
+//	    withPort(8080),
+//	})
+//
+//	// Apply to zero value
+//	config := Build(configBuilder)
+//	// Result: Config{Host: "localhost", Port: 8080}
+//
+// # Example - Empty Slice
+//
+//	// Empty slice returns identity
+//	identity := ConcatAll([]Endomorphism[int]{})
+//	result := identity(42) // Returns: 42
+//
+// # Relationship to Monoid
+//
+// ConcatAll is equivalent to using M.ConcatAll with the endomorphism Monoid:
+//
+//	import M "github.com/IBM/fp-go/v2/monoid"
+//
+//	// These are equivalent:
+//	result1 := ConcatAll(endomorphisms)
+//	result2 := M.ConcatAll(Monoid[T]())(endomorphisms)
+//
+// # Use Cases
+//
+//  1. **Pipeline Construction**: Build transformation pipelines from individual steps
+//  2. **Configuration Building**: Combine multiple configuration setters
+//  3. **Data Transformation**: Chain multiple data transformations
+//  4. **Middleware Composition**: Combine middleware functions
+//  5. **Validation Chains**: Compose multiple validation functions
+func ConcatAll[T any](es []Endomorphism[T]) Endomorphism[T] {
+	return A.Reduce(es, MonadCompose[T], function.Identity[T])
+}
+
+// Reduce applies a slice of endomorphisms to the zero value of type T in LEFT-TO-RIGHT order.
+//
+// This function is a convenience wrapper that:
+//  1. Starts with the zero value of type T
+//  2. Applies each endomorphism in the slice from left to right
+//  3. Returns the final transformed value
+//
+// IMPORTANT: Execution order is LEFT-TO-RIGHT:
+//   - Reduce([]Endomorphism{f, g, h}) applies f first, then g, then h
+//   - This is the opposite of ConcatAll's RIGHT-TO-LEFT order
+//   - Each endomorphism receives the result of the previous one
+//
+// This is equivalent to: Build(ConcatAll(reverse(es))) but more efficient and clearer
+// for left-to-right sequential application.
+//
+// # Type Parameters
+//
+//   - T: The type being transformed
+//
+// # Parameters
+//
+//   - es: A slice of endomorphisms to apply sequentially
+//
+// # Returns
+//
+//	The final value after applying all endomorphisms to the zero value
+//
+// # Example - Sequential Transformations
+//
+//	double := N.Mul(2)
+//	increment := N.Add(1)
+//	square := func(x int) int { return x * x }
+//
+//	// Apply transformations LEFT-TO-RIGHT
+//	result := Reduce([]Endomorphism[int]{double, increment, square})
+//	// Execution: 0 -> double(0) = 0 -> increment(0) = 1 -> square(1) = 1
+//	// Result: 1
+//
+//	// With a non-zero starting point, use a custom initial value:
+//	addTen := N.Add(10)
+//	result2 := Reduce([]Endomorphism[int]{addTen, double, increment})
+//	// Execution: 0 -> addTen(0) = 10 -> double(10) = 20 -> increment(20) = 21
+//	// Result: 21
+//
+// # Example - Building a String
+//
+//	appendHello := func(s string) string { return s + "Hello" }
+//	appendSpace := func(s string) string { return s + " " }
+//	appendWorld := func(s string) string { return s + "World" }
+//
+//	// Build string LEFT-TO-RIGHT
+//	result := Reduce([]Endomorphism[string]{
+//	    appendHello,
+//	    appendSpace,
+//	    appendWorld,
+//	})
+//	// Execution: "" -> "Hello" -> "Hello " -> "Hello World"
+//	// Result: "Hello World"
+//
+// # Example - Configuration Building
+//
+//	type Settings struct {
+//	    Theme    string
+//	    FontSize int
+//	}
+//
+//	withTheme := func(theme string) Endomorphism[Settings] {
+//	    return func(s Settings) Settings {
+//	        s.Theme = theme
+//	        return s
+//	    }
+//	}
+//
+//	withFontSize := func(size int) Endomorphism[Settings] {
+//	    return func(s Settings) Settings {
+//	        s.FontSize = size
+//	        return s
+//	    }
+//	}
+//
+//	// Build settings LEFT-TO-RIGHT
+//	settings := Reduce([]Endomorphism[Settings]{
+//	    withTheme("dark"),
+//	    withFontSize(14),
+//	})
+//	// Result: Settings{Theme: "dark", FontSize: 14}
+//
+// # Comparison with ConcatAll
+//
+//	// ConcatAll: RIGHT-TO-LEFT composition, returns endomorphism
+//	endo := ConcatAll([]Endomorphism[int]{f, g, h})
+//	result1 := endo(value) // Applies h, then g, then f
+//
+//	// Reduce: LEFT-TO-RIGHT application, returns final value
+//	result2 := Reduce([]Endomorphism[int]{f, g, h})
+//	// Applies f to zero, then g, then h
+//
+// # Use Cases
+//
+//  1. **Sequential Processing**: Apply transformations in order
+//  2. **Pipeline Execution**: Execute a pipeline from start to finish
+//  3. **Builder Pattern**: Build objects step by step
+//  4. **State Machines**: Apply state transitions in sequence
+//  5. **Data Flow**: Transform data through multiple stages
+func Reduce[T any](es []Endomorphism[T]) T {
+	var t T
+	return A.Reduce(es, func(t T, e Endomorphism[T]) T { return e(t) }, t)
+}

v2/endomorphism/builder_example_test.go

@@ -0,0 +1,254 @@
+// 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 endomorphism_test
+
+import (
+	"fmt"
+	"time"
+
+	A "github.com/IBM/fp-go/v2/array"
+	"github.com/IBM/fp-go/v2/endomorphism"
+	M "github.com/IBM/fp-go/v2/monoid"
+	N "github.com/IBM/fp-go/v2/number"
+)
+
+// Example_build_basicUsage demonstrates basic usage of the Build function
+// to construct a value from the zero value using endomorphisms.
+func Example_build_basicUsage() {
+	// Define simple endomorphisms
+	addTen := N.Add(10)
+	double := N.Mul(2)
+
+	// Compose them using monoid (RIGHT-TO-LEFT execution)
+	// double is applied first, then addTen
+	builder := M.ConcatAll(endomorphism.Monoid[int]())(A.From(
+		addTen,
+		double,
+	))
+
+	// Build from zero value: 0 * 2 = 0, 0 + 10 = 10
+	result := endomorphism.Build(builder)
+	fmt.Println(result)
+	// Output: 10
+}
+
+// Example_build_configBuilder demonstrates using Build as a configuration builder pattern.
+func Example_build_configBuilder() {
+	type Config struct {
+		Host    string
+		Port    int
+		Timeout time.Duration
+		Debug   bool
+	}
+
+	// Define builder functions as endomorphisms
+	withHost := func(host string) endomorphism.Endomorphism[Config] {
+		return func(c Config) Config {
+			c.Host = host
+			return c
+		}
+	}
+
+	withPort := func(port int) endomorphism.Endomorphism[Config] {
+		return func(c Config) Config {
+			c.Port = port
+			return c
+		}
+	}
+
+	withTimeout := func(d time.Duration) endomorphism.Endomorphism[Config] {
+		return func(c Config) Config {
+			c.Timeout = d
+			return c
+		}
+	}
+
+	withDebug := func(debug bool) endomorphism.Endomorphism[Config] {
+		return func(c Config) Config {
+			c.Debug = debug
+			return c
+		}
+	}
+
+	// Compose builders using monoid
+	configBuilder := M.ConcatAll(endomorphism.Monoid[Config]())([]endomorphism.Endomorphism[Config]{
+		withHost("localhost"),
+		withPort(8080),
+		withTimeout(30 * time.Second),
+		withDebug(true),
+	})
+
+	// Build the configuration from zero value
+	config := endomorphism.Build(configBuilder)
+
+	fmt.Printf("Host: %s\n", config.Host)
+	fmt.Printf("Port: %d\n", config.Port)
+	fmt.Printf("Timeout: %v\n", config.Timeout)
+	fmt.Printf("Debug: %v\n", config.Debug)
+	// Output:
+	// Host: localhost
+	// Port: 8080
+	// Timeout: 30s
+	// Debug: true
+}
+
+// Example_build_stringBuilder demonstrates building a string using endomorphisms.
+func Example_build_stringBuilder() {
+	// Define string transformation endomorphisms
+	appendHello := func(s string) string { return s + "Hello" }
+	appendSpace := func(s string) string { return s + " " }
+	appendWorld := func(s string) string { return s + "World" }
+	appendExclamation := func(s string) string { return s + "!" }
+
+	// Compose transformations (RIGHT-TO-LEFT execution)
+	stringBuilder := M.ConcatAll(endomorphism.Monoid[string]())([]endomorphism.Endomorphism[string]{
+		appendHello,
+		appendSpace,
+		appendWorld,
+		appendExclamation,
+	})
+
+	// Build the string from empty string
+	result := endomorphism.Build(stringBuilder)
+	fmt.Println(result)
+	// Output: !World Hello
+}
+
+// Example_build_personBuilder demonstrates building a complex struct using the builder pattern.
+func Example_build_personBuilder() {
+	type Person struct {
+		FirstName string
+		LastName  string
+		Age       int
+		Email     string
+	}
+
+	// Define builder functions
+	withFirstName := func(name string) endomorphism.Endomorphism[Person] {
+		return func(p Person) Person {
+			p.FirstName = name
+			return p
+		}
+	}
+
+	withLastName := func(name string) endomorphism.Endomorphism[Person] {
+		return func(p Person) Person {
+			p.LastName = name
+			return p
+		}
+	}
+
+	withAge := func(age int) endomorphism.Endomorphism[Person] {
+		return func(p Person) Person {
+			p.Age = age
+			return p
+		}
+	}
+
+	withEmail := func(email string) endomorphism.Endomorphism[Person] {
+		return func(p Person) Person {
+			p.Email = email
+			return p
+		}
+	}
+
+	// Build a person
+	personBuilder := M.ConcatAll(endomorphism.Monoid[Person]())([]endomorphism.Endomorphism[Person]{
+		withFirstName("Alice"),
+		withLastName("Smith"),
+		withAge(30),
+		withEmail("alice.smith@example.com"),
+	})
+
+	person := endomorphism.Build(personBuilder)
+
+	fmt.Printf("%s %s, Age: %d, Email: %s\n",
+		person.FirstName, person.LastName, person.Age, person.Email)
+	// Output: Alice Smith, Age: 30, Email: alice.smith@example.com
+}
+
+// Example_build_conditionalBuilder demonstrates conditional building using endomorphisms.
+func Example_build_conditionalBuilder() {
+	type Settings struct {
+		Theme      string
+		FontSize   int
+		AutoSave   bool
+		Animations bool
+	}
+
+	withTheme := func(theme string) endomorphism.Endomorphism[Settings] {
+		return func(s Settings) Settings {
+			s.Theme = theme
+			return s
+		}
+	}
+
+	withFontSize := func(size int) endomorphism.Endomorphism[Settings] {
+		return func(s Settings) Settings {
+			s.FontSize = size
+			return s
+		}
+	}
+
+	withAutoSave := func(enabled bool) endomorphism.Endomorphism[Settings] {
+		return func(s Settings) Settings {
+			s.AutoSave = enabled
+			return s
+		}
+	}
+
+	withAnimations := func(enabled bool) endomorphism.Endomorphism[Settings] {
+		return func(s Settings) Settings {
+			s.Animations = enabled
+			return s
+		}
+	}
+
+	// Build settings conditionally
+	isDarkMode := true
+	isAccessibilityMode := true
+
+	// Note: Monoid executes RIGHT-TO-LEFT, so later items in the slice are applied first
+	// We need to add items in reverse order for the desired effect
+	builders := []endomorphism.Endomorphism[Settings]{}
+
+	if isAccessibilityMode {
+		builders = append(builders, withFontSize(18)) // Will be applied last (overrides)
+		builders = append(builders, withAnimations(false))
+	}
+
+	if isDarkMode {
+		builders = append(builders, withTheme("dark"))
+	} else {
+		builders = append(builders, withTheme("light"))
+	}
+
+	builders = append(builders, withAutoSave(true))
+	builders = append(builders, withFontSize(14)) // Will be applied first
+
+	settingsBuilder := M.ConcatAll(endomorphism.Monoid[Settings]())(builders)
+	settings := endomorphism.Build(settingsBuilder)
+
+	fmt.Printf("Theme: %s\n", settings.Theme)
+	fmt.Printf("FontSize: %d\n", settings.FontSize)
+	fmt.Printf("AutoSave: %v\n", settings.AutoSave)
+	fmt.Printf("Animations: %v\n", settings.Animations)
+	// Output:
+	// Theme: dark
+	// FontSize: 18
+	// AutoSave: true
+	// Animations: false
+}

v2/endomorphism/doc.go

@@ -37,7 +37,7 @@
 //
 //	// Define some endomorphisms
 //	double := N.Mul(2)
-//	increment := func(x int) int { return x + 1 }
+//	increment := N.Add(1)
 //
 //	// Compose them (RIGHT-TO-LEFT execution)
 //	composed := endomorphism.Compose(double, increment)
@@ -63,8 +63,8 @@
 //	// Combine multiple endomorphisms (RIGHT-TO-LEFT execution)
 //	combined := M.ConcatAll(monoid)(
 //		N.Mul(2),  // applied third
-//		func(x int) int { return x + 1 },  // applied second
-//		func(x int) int { return x * 3 },  // applied first
+//		N.Add(1),  // applied second
+//		N.Mul(3),  // applied first
 //	)
 //	result := combined(5) // (5 * 3) = 15, (15 + 1) = 16, (16 * 2) = 32
 //
@@ -75,7 +75,7 @@
 //
 //	// Chain allows sequencing of endomorphisms (LEFT-TO-RIGHT)
 //	f := N.Mul(2)
-//	g := func(x int) int { return x + 1 }
+//	g := N.Add(1)
 //	chained := endomorphism.MonadChain(f, g)  // f first, then g
 //	result := chained(5) // (5 * 2) + 1 = 11
 //
@@ -84,7 +84,7 @@
 // The key difference between Compose and Chain/MonadChain is execution order:
 //
 //	double := N.Mul(2)
-//	increment := func(x int) int { return x + 1 }
+//	increment := N.Add(1)
 //
 //	// Compose: RIGHT-TO-LEFT (mathematical composition)
 //	composed := endomorphism.Compose(double, increment)

v2/endomorphism/endo.go

@@ -38,7 +38,7 @@ import (
 // Example:
 //
 //	double := N.Mul(2)
-//	increment := func(x int) int { return x + 1 }
+//	increment := N.Add(1)
 //	result := endomorphism.MonadAp(double, increment) // Composes: double ∘ increment
 //	// result(5) = double(increment(5)) = double(6) = 12
 func MonadAp[A any](fab Endomorphism[A], fa Endomorphism[A]) Endomorphism[A] {
@@ -62,7 +62,7 @@ func MonadAp[A any](fab Endomorphism[A], fa Endomorphism[A]) Endomorphism[A] {
 //
 // Example:
 //
-//	increment := func(x int) int { return x + 1 }
+//	increment := N.Add(1)
 //	applyIncrement := endomorphism.Ap(increment)
 //	double := N.Mul(2)
 //	composed := applyIncrement(double) // double ∘ increment
@@ -92,7 +92,7 @@ func Ap[A any](fa Endomorphism[A]) Operator[A] {
 // Example:
 //
 //	double := N.Mul(2)
-//	increment := func(x int) int { return x + 1 }
+//	increment := N.Add(1)
 //
 //	// MonadCompose executes RIGHT-TO-LEFT: increment first, then double
 //	composed := endomorphism.MonadCompose(double, increment)
@@ -124,7 +124,7 @@ func MonadCompose[A any](f, g Endomorphism[A]) Endomorphism[A] {
 // Example:
 //
 //	double := N.Mul(2)
-//	increment := func(x int) int { return x + 1 }
+//	increment := N.Add(1)
 //	mapped := endomorphism.MonadMap(double, increment)
 //	// mapped(5) = double(increment(5)) = double(6) = 12
 func MonadMap[A any](f, g Endomorphism[A]) Endomorphism[A] {
@@ -151,7 +151,7 @@ func MonadMap[A any](f, g Endomorphism[A]) Endomorphism[A] {
 //
 // Example:
 //
-//	increment := func(x int) int { return x + 1 }
+//	increment := N.Add(1)
 //	composeWithIncrement := endomorphism.Compose(increment)
 //	double := N.Mul(2)
 //
@@ -188,7 +188,7 @@ func Compose[A any](g Endomorphism[A]) Operator[A] {
 //
 //	double := N.Mul(2)
 //	mapDouble := endomorphism.Map(double)
-//	increment := func(x int) int { return x + 1 }
+//	increment := N.Add(1)
 //	mapped := mapDouble(increment)
 //	// mapped(5) = double(increment(5)) = double(6) = 12
 func Map[A any](f Endomorphism[A]) Operator[A] {
@@ -216,7 +216,7 @@ func Map[A any](f Endomorphism[A]) Operator[A] {
 // Example:
 //
 //	double := N.Mul(2)
-//	increment := func(x int) int { return x + 1 }
+//	increment := N.Add(1)
 //
 //	// MonadChain executes LEFT-TO-RIGHT: double first, then increment
 //	chained := endomorphism.MonadChain(double, increment)
@@ -294,7 +294,7 @@ func ChainFirst[A any](f Endomorphism[A]) Operator[A] {
 //
 // Example:
 //
-//	increment := func(x int) int { return x + 1 }
+//	increment := N.Add(1)
 //	chainWithIncrement := endomorphism.Chain(increment)
 //	double := N.Mul(2)
 //

v2/endomorphism/endomorphism_test.go

@@ -206,7 +206,7 @@ func TestCompose(t *testing.T) {
 // TestMonadComposeVsCompose demonstrates the relationship between MonadCompose and Compose
 func TestMonadComposeVsCompose(t *testing.T) {
 	double := N.Mul(2)
-	increment := func(x int) int { return x + 1 }
+	increment := N.Add(1)
 
 	// MonadCompose takes both functions at once
 	monadComposed := MonadCompose(double, increment)
@@ -458,7 +458,7 @@ func BenchmarkCompose(b *testing.B) {
 // TestComposeVsChain demonstrates the key difference between Compose and Chain
 func TestComposeVsChain(t *testing.T) {
 	double := N.Mul(2)
-	increment := func(x int) int { return x + 1 }
+	increment := N.Add(1)
 
 	// Compose executes RIGHT-TO-LEFT
 	// Compose(double, increment) means: increment first, then double
@@ -722,3 +722,352 @@ func TestChainFirst(t *testing.T) {
 	// But side effect should have been executed with double's result
 	assert.Equal(t, 10, sideEffect, "ChainFirst should execute second function for effect")
 }
+
+// TestBuild tests the Build function
+func TestBuild(t *testing.T) {
+	t.Run("build with single transformation", func(t *testing.T) {
+		// Build applies endomorphism to zero value
+		result := Build(double)
+		assert.Equal(t, 0, result, "Build(double) on zero value should be 0")
+	})
+
+	t.Run("build with composed transformations", func(t *testing.T) {
+		// Create a builder that starts from zero and applies transformations
+		builder := M.ConcatAll(Monoid[int]())([]Endomorphism[int]{
+			N.Add(10),
+			N.Mul(2),
+			N.Add(5),
+		})
+
+		result := Build(builder)
+		// RIGHT-TO-LEFT: 0 + 5 = 5, 5 * 2 = 10, 10 + 10 = 20
+		assert.Equal(t, 20, result, "Build should apply composed transformations to zero value")
+	})
+
+	t.Run("build with identity", func(t *testing.T) {
+		result := Build(Identity[int]())
+		assert.Equal(t, 0, result, "Build(identity) should return zero value")
+	})
+
+	t.Run("build string from empty", func(t *testing.T) {
+		builder := M.ConcatAll(Monoid[string]())([]Endomorphism[string]{
+			func(s string) string { return s + "Hello" },
+			func(s string) string { return s + " " },
+			func(s string) string { return s + "World" },
+		})
+
+		result := Build(builder)
+		// RIGHT-TO-LEFT: "" + "World" = "World", "World" + " " = "World ", "World " + "Hello" = "World Hello"
+		assert.Equal(t, "World Hello", result, "Build should work with strings")
+	})
+
+	t.Run("build struct with builder pattern", func(t *testing.T) {
+		type Config struct {
+			Host string
+			Port int
+		}
+
+		withHost := func(host string) Endomorphism[Config] {
+			return func(c Config) Config {
+				c.Host = host
+				return c
+			}
+		}
+
+		withPort := func(port int) Endomorphism[Config] {
+			return func(c Config) Config {
+				c.Port = port
+				return c
+			}
+		}
+
+		builder := M.ConcatAll(Monoid[Config]())([]Endomorphism[Config]{
+			withHost("localhost"),
+			withPort(8080),
+		})
+
+		result := Build(builder)
+		assert.Equal(t, "localhost", result.Host, "Build should set Host")
+		assert.Equal(t, 8080, result.Port, "Build should set Port")
+	})
+
+	t.Run("build slice with operations", func(t *testing.T) {
+		type IntSlice []int
+
+		appendValue := func(v int) Endomorphism[IntSlice] {
+			return func(s IntSlice) IntSlice {
+				return append(s, v)
+			}
+		}
+
+		builder := M.ConcatAll(Monoid[IntSlice]())([]Endomorphism[IntSlice]{
+			appendValue(1),
+			appendValue(2),
+			appendValue(3),
+		})
+
+		result := Build(builder)
+		// RIGHT-TO-LEFT: append 3, append 2, append 1
+		assert.Equal(t, IntSlice{3, 2, 1}, result, "Build should construct slice")
+	})
+}
+
+// TestBuildAsBuilderPattern demonstrates using Build as a builder pattern
+func TestBuildAsBuilderPattern(t *testing.T) {
+	type Person struct {
+		Name   string
+		Age    int
+		Email  string
+		Active bool
+	}
+
+	// Define builder functions
+	withName := func(name string) Endomorphism[Person] {
+		return func(p Person) Person {
+			p.Name = name
+			return p
+		}
+	}
+
+	withAge := func(age int) Endomorphism[Person] {
+		return func(p Person) Person {
+			p.Age = age
+			return p
+		}
+	}
+
+	withEmail := func(email string) Endomorphism[Person] {
+		return func(p Person) Person {
+			p.Email = email
+			return p
+		}
+	}
+
+	withActive := func(active bool) Endomorphism[Person] {
+		return func(p Person) Person {
+			p.Active = active
+			return p
+		}
+	}
+
+	// Build a person using the builder pattern
+	personBuilder := M.ConcatAll(Monoid[Person]())([]Endomorphism[Person]{
+		withName("Alice"),
+		withAge(30),
+		withEmail("alice@example.com"),
+		withActive(true),
+	})
+
+	person := Build(personBuilder)
+
+	assert.Equal(t, "Alice", person.Name)
+	assert.Equal(t, 30, person.Age)
+	assert.Equal(t, "alice@example.com", person.Email)
+	assert.True(t, person.Active)
+}
+
+// TestConcatAll tests the ConcatAll function
+func TestConcatAll(t *testing.T) {
+	t.Run("concat all with multiple endomorphisms", func(t *testing.T) {
+		// ConcatAll executes RIGHT-TO-LEFT
+		combined := ConcatAll([]Endomorphism[int]{double, increment, square})
+		result := combined(5)
+		// RIGHT-TO-LEFT: square(5) = 25, increment(25) = 26, double(26) = 52
+		assert.Equal(t, 52, result, "ConcatAll should execute right-to-left")
+	})
+
+	t.Run("concat all with empty slice", func(t *testing.T) {
+		// Empty slice should return identity
+		identity := ConcatAll([]Endomorphism[int]{})
+		result := identity(42)
+		assert.Equal(t, 42, result, "ConcatAll with empty slice should return identity")
+	})
+
+	t.Run("concat all with single endomorphism", func(t *testing.T) {
+		combined := ConcatAll([]Endomorphism[int]{double})
+		result := combined(5)
+		assert.Equal(t, 10, result, "ConcatAll with single endomorphism should apply it")
+	})
+
+	t.Run("concat all with two endomorphisms", func(t *testing.T) {
+		// RIGHT-TO-LEFT: increment first, then double
+		combined := ConcatAll([]Endomorphism[int]{double, increment})
+		result := combined(5)
+		assert.Equal(t, 12, result, "ConcatAll should execute right-to-left: (5 + 1) * 2 = 12")
+	})
+
+	t.Run("concat all with strings", func(t *testing.T) {
+		appendHello := func(s string) string { return s + "Hello" }
+		appendSpace := func(s string) string { return s + " " }
+		appendWorld := func(s string) string { return s + "World" }
+
+		// RIGHT-TO-LEFT execution
+		combined := ConcatAll([]Endomorphism[string]{appendHello, appendSpace, appendWorld})
+		result := combined("")
+		// RIGHT-TO-LEFT: "" + "World" = "World", "World" + " " = "World ", "World " + "Hello" = "World Hello"
+		assert.Equal(t, "World Hello", result, "ConcatAll should work with strings")
+	})
+
+	t.Run("concat all for building structs", func(t *testing.T) {
+		type Config struct {
+			Host string
+			Port int
+		}
+
+		withHost := func(host string) Endomorphism[Config] {
+			return func(c Config) Config {
+				c.Host = host
+				return c
+			}
+		}
+
+		withPort := func(port int) Endomorphism[Config] {
+			return func(c Config) Config {
+				c.Port = port
+				return c
+			}
+		}
+
+		combined := ConcatAll([]Endomorphism[Config]{
+			withHost("localhost"),
+			withPort(8080),
+		})
+
+		result := combined(Config{})
+		assert.Equal(t, "localhost", result.Host)
+		assert.Equal(t, 8080, result.Port)
+	})
+
+	t.Run("concat all is equivalent to monoid ConcatAll", func(t *testing.T) {
+		endos := []Endomorphism[int]{double, increment, square}
+
+		result1 := ConcatAll(endos)(5)
+		result2 := M.ConcatAll(Monoid[int]())(endos)(5)
+
+		assert.Equal(t, result1, result2, "ConcatAll should be equivalent to M.ConcatAll(Monoid())")
+	})
+}
+
+// TestReduce tests the Reduce function
+func TestReduce(t *testing.T) {
+	t.Run("reduce with multiple endomorphisms", func(t *testing.T) {
+		// Reduce executes LEFT-TO-RIGHT starting from zero value
+		result := Reduce([]Endomorphism[int]{double, increment, square})
+		// LEFT-TO-RIGHT: 0 -> double(0) = 0 -> increment(0) = 1 -> square(1) = 1
+		assert.Equal(t, 1, result, "Reduce should execute left-to-right from zero value")
+	})
+
+	t.Run("reduce with empty slice", func(t *testing.T) {
+		// Empty slice should return zero value
+		result := Reduce([]Endomorphism[int]{})
+		assert.Equal(t, 0, result, "Reduce with empty slice should return zero value")
+	})
+
+	t.Run("reduce with single endomorphism", func(t *testing.T) {
+		addTen := N.Add(10)
+		result := Reduce([]Endomorphism[int]{addTen})
+		// 0 + 10 = 10
+		assert.Equal(t, 10, result, "Reduce with single endomorphism should apply it to zero")
+	})
+
+	t.Run("reduce with sequential transformations", func(t *testing.T) {
+		addTen := N.Add(10)
+		// LEFT-TO-RIGHT: 0 -> addTen(0) = 10 -> double(10) = 20 -> increment(20) = 21
+		result := Reduce([]Endomorphism[int]{addTen, double, increment})
+		assert.Equal(t, 21, result, "Reduce should apply transformations left-to-right")
+	})
+
+	t.Run("reduce with strings", func(t *testing.T) {
+		appendHello := func(s string) string { return s + "Hello" }
+		appendSpace := func(s string) string { return s + " " }
+		appendWorld := func(s string) string { return s + "World" }
+
+		// LEFT-TO-RIGHT execution
+		result := Reduce([]Endomorphism[string]{appendHello, appendSpace, appendWorld})
+		// "" -> "Hello" -> "Hello " -> "Hello World"
+		assert.Equal(t, "Hello World", result, "Reduce should work with strings left-to-right")
+	})
+
+	t.Run("reduce for building structs", func(t *testing.T) {
+		type Settings struct {
+			Theme    string
+			FontSize int
+		}
+
+		withTheme := func(theme string) Endomorphism[Settings] {
+			return func(s Settings) Settings {
+				s.Theme = theme
+				return s
+			}
+		}
+
+		withFontSize := func(size int) Endomorphism[Settings] {
+			return func(s Settings) Settings {
+				s.FontSize = size
+				return s
+			}
+		}
+
+		// LEFT-TO-RIGHT application
+		result := Reduce([]Endomorphism[Settings]{
+			withTheme("dark"),
+			withFontSize(14),
+		})
+
+		assert.Equal(t, "dark", result.Theme)
+		assert.Equal(t, 14, result.FontSize)
+	})
+
+	t.Run("reduce is equivalent to Build(ConcatAll(reverse))", func(t *testing.T) {
+		addTen := N.Add(10)
+		endos := []Endomorphism[int]{addTen, double, increment}
+
+		// Reduce applies left-to-right
+		result1 := Reduce(endos)
+
+		// Reverse and use ConcatAll (which is right-to-left)
+		reversed := []Endomorphism[int]{increment, double, addTen}
+		result2 := Build(ConcatAll(reversed))
+
+		assert.Equal(t, result1, result2, "Reduce should be equivalent to Build(ConcatAll(reverse))")
+	})
+}
+
+// TestConcatAllVsReduce demonstrates the difference between ConcatAll and Reduce
+func TestConcatAllVsReduce(t *testing.T) {
+	addTen := N.Add(10)
+
+	endos := []Endomorphism[int]{addTen, double, increment}
+
+	// ConcatAll: RIGHT-TO-LEFT composition, returns endomorphism
+	concatResult := ConcatAll(endos)(5)
+	// 5 -> increment(5) = 6 -> double(6) = 12 -> addTen(12) = 22
+
+	// Reduce: LEFT-TO-RIGHT application, returns value from zero
+	reduceResult := Reduce(endos)
+	// 0 -> addTen(0) = 10 -> double(10) = 20 -> increment(20) = 21
+
+	assert.NotEqual(t, concatResult, reduceResult, "ConcatAll and Reduce should produce different results")
+	assert.Equal(t, 22, concatResult, "ConcatAll should execute right-to-left on input value")
+	assert.Equal(t, 21, reduceResult, "Reduce should execute left-to-right from zero value")
+}
+
+// TestReduceWithBuild demonstrates using Reduce vs Build with ConcatAll
+func TestReduceWithBuild(t *testing.T) {
+	addFive := N.Add(5)
+	multiplyByThree := N.Mul(3)
+
+	endos := []Endomorphism[int]{addFive, multiplyByThree}
+
+	// Reduce: LEFT-TO-RIGHT from zero
+	reduceResult := Reduce(endos)
+	// 0 -> addFive(0) = 5 -> multiplyByThree(5) = 15
+	assert.Equal(t, 15, reduceResult)
+
+	// Build with ConcatAll: RIGHT-TO-LEFT from zero
+	buildResult := Build(ConcatAll(endos))
+	// 0 -> multiplyByThree(0) = 0 -> addFive(0) = 5
+	assert.Equal(t, 5, buildResult)
+
+	assert.NotEqual(t, reduceResult, buildResult, "Reduce and Build(ConcatAll) produce different results due to execution order")
+}

v2/endomorphism/monoid.go

@@ -104,7 +104,7 @@ func Identity[A any]() Endomorphism[A] {
 //
 //	sg := endomorphism.Semigroup[int]()
 //	double := N.Mul(2)
-//	increment := func(x int) int { return x + 1 }
+//	increment := N.Add(1)
 //
 //	// Combine using the semigroup (RIGHT-TO-LEFT execution)
 //	combined := sg.Concat(double, increment)
@@ -140,7 +140,7 @@ func Semigroup[A any]() S.Semigroup[Endomorphism[A]] {
 //
 //	monoid := endomorphism.Monoid[int]()
 //	double := N.Mul(2)
-//	increment := func(x int) int { return x + 1 }
+//	increment := N.Add(1)
 //	square := func(x int) int { return x * x }
 //
 //	// Combine multiple endomorphisms (RIGHT-TO-LEFT execution)

v2/endomorphism/types.go

@@ -30,7 +30,7 @@ type (
 	//
 	//	// Simple endomorphisms on integers
 	//	double := N.Mul(2)
-	//	increment := func(x int) int { return x + 1 }
+	//	increment := N.Add(1)
 	//
 	//	// Both are endomorphisms of type Endomorphism[int]
 	//	var f endomorphism.Endomorphism[int] = double

v2/idiomatic/REVIEW_SUMMARY.md

@@ -0,0 +1,226 @@
+# Idiomatic Package Review Summary
+
+**Date:** 2025-11-26  
+**Reviewer:** Code Review Assistant
+
+## Overview
+
+This document summarizes the comprehensive review of the `idiomatic` package and its subpackages, including documentation fixes, additions, and test coverage analysis.
+
+## Documentation Improvements
+
+### 1. Main Package (`idiomatic/`)
+- ✅ **Status:** Documentation is comprehensive and well-structured
+- **File:** `doc.go` (505 lines)
+- **Quality:** Excellent - includes overview, performance comparisons, usage examples, and best practices
+
+### 2. Option Package (`idiomatic/option/`)
+- ✅ **Fixed:** Added missing copyright headers to `types.go` and `function.go`
+- ✅ **Fixed:** Added comprehensive documentation for type aliases in `types.go`
+- ✅ **Fixed:** Enhanced function documentation in `function.go` with examples
+- ✅ **Fixed:** Added missing documentation for `FromZero`, `FromNonZero`, and `FromEq` functions
+- **Files Updated:**
+  - `types.go` - Added copyright header and type documentation
+  - `function.go` - Added copyright header and improved function docs
+  - `option.go` - Enhanced documentation for utility functions
+
+### 3. Result Package (`idiomatic/result/`)
+- ✅ **Fixed:** Added missing copyright header to `function.go`
+- ✅ **Fixed:** Enhanced function documentation with examples
+- **Files Updated:**
+  - `function.go` - Added copyright header and improved documentation
+  - `types.go` - Already had good documentation
+
+### 4. IOResult Package (`idiomatic/ioresult/`)
+- ✅ **Status:** Documentation is comprehensive
+- **File:** `doc.go` (198 lines)
+- **Quality:** Excellent - includes detailed explanations of IO operations, lazy evaluation, and side effects
+
+### 5. ReaderIOResult Package (`idiomatic/readerioresult/`)
+- ✅ **Created:** New `doc.go` file (96 lines)
+- ✅ **Fixed:** Added comprehensive type documentation to `types.go`
+- **New Documentation Includes:**
+  - Package overview and use cases
+  - Basic usage examples
+  - Composition patterns
+  - Error handling strategies
+  - Relationship to other monads
+
+### 6. ReaderResult Package (`idiomatic/readerresult/`)
+- ✅ **Fixed:** Added comprehensive type documentation to `types.go`
+- **Existing:** `doc.go` already present (178 lines) with excellent documentation
+
+## Test Coverage Analysis
+
+### Option Package Tests
+**File:** `idiomatic/option/option_test.go`
+
+**Existing Coverage:**
+- ✅ `IsNone` - Tested
+- ✅ `IsSome` - Tested
+- ✅ `Map` - Tested
+- ✅ `Ap` - Tested
+- ✅ `Chain` - Tested
+- ✅ `ChainTo` - Comprehensive tests with multiple scenarios
+
+**Missing Tests (Commented Out):**
+- ⚠️ `Flatten` - Test commented out
+- ⚠️ `Fold` - Test commented out
+- ⚠️ `FromPredicate` - Test commented out
+- ⚠️ `Alt` - Test commented out
+
+**Recommendations:**
+1. Uncomment and fix the commented-out tests
+2. Add tests for:
+   - `FromZero`
+   - `FromNonZero`
+   - `FromEq`
+   - `FromNillable`
+   - `MapTo`
+   - `GetOrElse`
+   - `ChainFirst`
+   - `Reduce`
+   - `Filter`
+   - `Flap`
+   - `ToString`
+
+### Result Package Tests
+**File:** `idiomatic/result/either_test.go`
+
+**Existing Coverage:**
+- ✅ `IsLeft` - Tested
+- ✅ `IsRight` - Tested
+- ✅ `Map` - Tested
+- ✅ `Ap` - Tested
+- ✅ `Alt` - Tested
+- ✅ `ChainFirst` - Tested
+- ✅ `ChainOptionK` - Tested
+- ✅ `FromOption` - Tested
+- ✅ `ToString` - Tested
+
+**Missing Tests:**
+- ⚠️ `Of` - Not explicitly tested
+- ⚠️ `BiMap` - Not tested
+- ⚠️ `MapTo` - Not tested
+- ⚠️ `MapLeft` - Not tested
+- ⚠️ `Chain` - Not tested
+- ⚠️ `ChainTo` - Not tested
+- ⚠️ `ToOption` - Not tested
+- ⚠️ `FromError` - Not tested
+- ⚠️ `ToError` - Not tested
+- ⚠️ `Fold` - Not tested
+- ⚠️ `FromPredicate` - Not tested
+- ⚠️ `FromNillable` - Not tested
+- ⚠️ `GetOrElse` - Not tested
+- ⚠️ `Reduce` - Not tested
+- ⚠️ `OrElse` - Not tested
+- ⚠️ `ToType` - Not tested
+- ⚠️ `Memoize` - Not tested
+- ⚠️ `Flap` - Not tested
+
+### IOResult Package Tests
+**File:** `idiomatic/ioresult/monad_test.go`
+
+**Existing Coverage:** ✅ **EXCELLENT**
+- ✅ Comprehensive monad law tests (left identity, right identity, associativity)
+- ✅ Functor law tests (composition, identity)
+- ✅ Pointed, Functor, and Monad interface tests
+- ✅ Parallel vs Sequential execution tests
+- ✅ Integration tests with complex pipelines
+- ✅ Error handling scenarios
+
+**Status:** This package has exemplary test coverage and can serve as a model for other packages.
+
+### ReaderIOResult Package
+**Status:** ⚠️ **NO TESTS FOUND**
+
+**Recommendations:**
+Create comprehensive test suite covering:
+- Basic construction and execution
+- Map, Chain, Ap operations
+- Error handling
+- Environment dependency injection
+- Integration with IOResult
+
+### ReaderResult Package
+**Files:** Multiple test files exist
+- `array_test.go`
+- `bind_test.go`
+- `curry_test.go`
+- `from_test.go`
+- `monoid_test.go`
+- `reader_test.go`
+- `sequence_test.go`
+
+**Status:** ✅ Good coverage exists
+
+## Subpackages Review
+
+### Packages Requiring Review:
+1. **idiomatic/option/number/** - Needs documentation and test review
+2. **idiomatic/option/testing/** - Contains disabled test files (`laws_test._go`, `laws._go`)
+3. **idiomatic/result/exec/** - Needs review
+4. **idiomatic/result/http/** - Needs review
+5. **idiomatic/result/testing/** - Contains disabled test files
+6. **idiomatic/ioresult/exec/** - Needs review
+7. **idiomatic/ioresult/file/** - Needs review
+8. **idiomatic/ioresult/http/** - Needs review
+9. **idiomatic/ioresult/http/builder/** - Needs review
+10. **idiomatic/ioresult/testing/** - Needs review
+
+## Priority Recommendations
+
+### High Priority
+1. **Enable Commented Tests:** Uncomment and fix tests in `option/option_test.go`
+2. **Add Missing Option Tests:** Create tests for all untested functions in option package
+3. **Add Missing Result Tests:** Create comprehensive test suite for result package
+4. **Create ReaderIOResult Tests:** This package has no tests at all
+
+### Medium Priority
+5. **Review Subpackages:** Systematically review exec, file, http, and testing subpackages
+6. **Enable Testing Package Tests:** Investigate why `laws_test._go` files are disabled
+
+### Low Priority
+7. **Benchmark Tests:** Consider adding benchmark tests for performance-critical operations
+8. **Property-Based Tests:** Consider adding property-based tests using testing/quick
+
+## Files Modified in This Review
+
+1. `idiomatic/option/types.go` - Added copyright and documentation
+2. `idiomatic/option/function.go` - Added copyright and enhanced docs
+3. `idiomatic/option/option.go` - Enhanced function documentation
+4. `idiomatic/result/function.go` - Added copyright and enhanced docs
+5. `idiomatic/readerioresult/doc.go` - **CREATED NEW FILE**
+6. `idiomatic/readerioresult/types.go` - Added comprehensive type docs
+7. `idiomatic/readerresult/types.go` - Added comprehensive type docs
+
+## Summary Statistics
+
+- **Packages Reviewed:** 6 main packages
+- **Documentation Files Created:** 1 (readerioresult/doc.go)
+- **Files Modified:** 7
+- **Lines of Documentation Added:** ~150+
+- **Test Coverage Status:**
+  - ✅ Excellent: ioresult
+  - ✅ Good: readerresult
+  - ⚠️ Needs Improvement: option, result
+  - ⚠️ Missing: readerioresult
+
+## Next Steps
+
+1. Create missing unit tests for option package functions
+2. Create missing unit tests for result package functions
+3. Create complete test suite for readerioresult package
+4. Review and document subpackages (exec, file, http, testing, number)
+5. Investigate and potentially enable disabled test files in testing subpackages
+6. Consider adding integration tests that demonstrate real-world usage patterns
+
+## Conclusion
+
+The idiomatic package has excellent documentation at the package level, with comprehensive explanations of concepts, usage patterns, and performance characteristics. The main areas for improvement are:
+
+1. **Test Coverage:** Several functions lack unit tests, particularly in option and result packages
+2. **Subpackage Documentation:** Some subpackages need documentation review
+3. **Disabled Tests:** Some test files are disabled and should be investigated
+
+The IOResult package serves as an excellent example of comprehensive testing, including monad law verification and integration tests. This approach should be replicated across other packages.

v2/idiomatic/doc.go

@@ -27,21 +27,21 @@
 // Unlike the standard fp-go packages (option, either, result) which use struct wrappers,
 // the idiomatic package uses Go's native tuple patterns:
 //
-//   Standard either:  Either[E, A]              (struct wrapper)
-//   Idiomatic result: (A, error)                (native Go tuple)
+//	Standard either:  Either[E, A]              (struct wrapper)
+//	Idiomatic result: (A, error)                (native Go tuple)
 //
-//   Standard option:  Option[A]                 (struct wrapper)
-//   Idiomatic option: (A, bool)                 (native Go tuple)
+//	Standard option:  Option[A]                 (struct wrapper)
+//	Idiomatic option: (A, bool)                 (native Go tuple)
 //
 // # Performance Benefits
 //
 // The idiomatic approach offers several performance advantages:
 //
-//  - Zero allocation for creating values (no heap allocations)
-//  - Better CPU cache locality (no pointer indirection)
-//  - Native Go compiler optimizations for tuples
-//  - Reduced garbage collection pressure
-//  - Smaller memory footprint
+//   - Zero allocation for creating values (no heap allocations)
+//   - Better CPU cache locality (no pointer indirection)
+//   - Native Go compiler optimizations for tuples
+//   - Reduced garbage collection pressure
+//   - Smaller memory footprint
 //
 // Benchmarks show 2-10x performance improvements for common operations compared to struct-based
 // implementations, especially for simple operations like Map, Chain, and Fold.
@@ -74,7 +74,7 @@
 //	none := option.None[int]()     // (0, false)
 //
 //	// Transforming values
-//	double := option.Map(func(x int) int { return x * 2 })
+//	double := option.Map(N.Mul(2))
 //	result := double(some)         // (84, true)
 //	result = double(none)          // (0, false)
 //
@@ -103,7 +103,7 @@
 //	failure := result.Left[int](errors.New("oops"))    // (0, error)
 //
 //	// Transforming values
-//	double := result.Map(func(x int) int { return x * 2 })
+//	double := result.Map(N.Mul(2))
 //	res := double(success)                             // (84, nil)
 //	res = double(failure)                              // (0, error)
 //
@@ -175,11 +175,11 @@
 //	)()
 //
 // Key features:
-//  - Lazy evaluation: Operations are not executed until the IOResult is called
-//  - Composable: Chain IO operations that may fail
-//  - Error handling: Automatic error propagation and recovery
-//  - Resource safety: Bracket ensures proper resource cleanup
-//  - Parallel execution: ApPar and TraverseArrayPar for concurrent operations
+//   - Lazy evaluation: Operations are not executed until the IOResult is called
+//   - Composable: Chain IO operations that may fail
+//   - Error handling: Automatic error propagation and recovery
+//   - Resource safety: Bracket ensures proper resource cleanup
+//   - Parallel execution: ApPar and TraverseArrayPar for concurrent operations
 //
 // # Type Signatures
 //
@@ -204,33 +204,33 @@
 // # When to Use Idiomatic vs Standard Packages
 //
 // Use idiomatic packages when:
-//  - Performance is critical (hot paths, tight loops)
-//  - You want zero-allocation functional patterns
-//  - You prefer Go's native error handling style
-//  - You're integrating with existing Go code that uses tuples
-//  - Memory efficiency matters (embedded systems, high-scale services)
-//  - You need IO operations with error handling (use ioresult)
+//   - Performance is critical (hot paths, tight loops)
+//   - You want zero-allocation functional patterns
+//   - You prefer Go's native error handling style
+//   - You're integrating with existing Go code that uses tuples
+//   - Memory efficiency matters (embedded systems, high-scale services)
+//   - You need IO operations with error handling (use ioresult)
 //
 // Use standard packages when:
-//  - You need full algebraic data type semantics
-//  - You're porting code from other FP languages
-//  - You want explicit Either[E, A] with custom error types
-//  - You need the complete suite of FP abstractions
-//  - Code clarity outweighs performance concerns
+//   - You need full algebraic data type semantics
+//   - You're porting code from other FP languages
+//   - You want explicit Either[E, A] with custom error types
+//   - You need the complete suite of FP abstractions
+//   - Code clarity outweighs performance concerns
 //
 // # Choosing Between result and ioresult
 //
 // Use result when:
-//  - Operations are pure (same input always produces same output)
-//  - No side effects are involved (no IO, no state mutation)
-//  - You want to represent success/failure without execution delay
+//   - Operations are pure (same input always produces same output)
+//   - No side effects are involved (no IO, no state mutation)
+//   - You want to represent success/failure without execution delay
 //
 // Use ioresult when:
-//  - Operations perform IO (file system, network, database)
-//  - Side effects are part of the computation
-//  - You need lazy evaluation (defer execution until needed)
-//  - You want to compose IO operations that may fail
-//  - Resource management is required (files, connections, locks)
+//   - Operations perform IO (file system, network, database)
+//   - Side effects are part of the computation
+//   - You need lazy evaluation (defer execution until needed)
+//   - You want to compose IO operations that may fail
+//   - Resource management is required (files, connections, locks)
 //
 // # Performance Comparison
 //
@@ -473,7 +473,7 @@
 //	    result, err := F.Pipe2(
 //	        input,
 //	        result.Right[int],
-//	        result.Map(func(x int) int { return x * 2 }),
+//	        result.Map(N.Mul(2)),
 //	    )
 //	    assert.NoError(t, err)
 //	    assert.Equal(t, 42, result)
@@ -483,7 +483,7 @@
 //	    value, ok := F.Pipe2(
 //	        42,
 //	        option.Some[int],
-//	        option.Map(func(x int) int { return x * 2 }),
+//	        option.Map(N.Mul(2)),
 //	    )
 //	    assert.True(t, ok)
 //	    assert.Equal(t, 84, value)

v2/idiomatic/ioresult/ap_test.go

@@ -20,6 +20,7 @@ import (
 	"testing"
 
 	F "github.com/IBM/fp-go/v2/function"
+	N "github.com/IBM/fp-go/v2/number"
 	"github.com/stretchr/testify/assert"
 )
 
@@ -147,7 +148,7 @@ func TestApFirst(t *testing.T) {
 		result := F.Pipe2(
 			Of(5),
 			ApFirst[int](Of("ignored")),
-			Map(func(x int) int { return x * 2 }),
+			Map(N.Mul(2)),
 		)
 
 		val, err := result()
@@ -298,7 +299,7 @@ func TestApSecond(t *testing.T) {
 		result := F.Pipe2(
 			Of(1),
 			ApSecond[int](Of(5)),
-			Map(func(x int) int { return x * 2 }),
+			Map(N.Mul(2)),
 		)
 
 		val, err := result()

v2/idiomatic/ioresult/bench_test.go

@@ -19,6 +19,7 @@ import (
 	"testing"
 
 	F "github.com/IBM/fp-go/v2/function"
+	N "github.com/IBM/fp-go/v2/number"
 )
 
 func BenchmarkOf(b *testing.B) {
@@ -29,7 +30,7 @@ func BenchmarkOf(b *testing.B) {
 
 func BenchmarkMap(b *testing.B) {
 	io := Of(42)
-	f := func(x int) int { return x * 2 }
+	f := N.Mul(2)
 
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
@@ -68,9 +69,9 @@ func BenchmarkBind(b *testing.B) {
 }
 
 func BenchmarkPipeline(b *testing.B) {
-	f1 := func(x int) int { return x + 1 }
-	f2 := func(x int) int { return x * 2 }
-	f3 := func(x int) int { return x - 3 }
+	f1 := N.Add(1)
+	f2 := N.Mul(2)
+	f3 := N.Sub(3)
 
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
@@ -93,9 +94,9 @@ func BenchmarkExecute(b *testing.B) {
 }
 
 func BenchmarkExecutePipeline(b *testing.B) {
-	f1 := func(x int) int { return x + 1 }
-	f2 := func(x int) int { return x * 2 }
-	f3 := func(x int) int { return x - 3 }
+	f1 := N.Add(1)
+	f2 := N.Mul(2)
+	f3 := N.Sub(3)
 
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
@@ -133,7 +134,7 @@ func BenchmarkLeft(b *testing.B) {
 
 func BenchmarkMapWithError(b *testing.B) {
 	io := Left[int](F.Constant[error](nil)())
-	f := func(x int) int { return x * 2 }
+	f := N.Mul(2)
 
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
@@ -194,7 +195,7 @@ func BenchmarkMonadApSecond(b *testing.B) {
 func BenchmarkFunctor(b *testing.B) {
 	functor := Functor[int, int]()
 	io := Of(42)
-	f := func(x int) int { return x * 2 }
+	f := N.Mul(2)
 
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {

v2/idiomatic/ioresult/doc.go

@@ -45,23 +45,23 @@
 //
 // IOResult provides two critical benefits:
 //
-// 1. **Lazy Evaluation**: The side effect doesn't happen when you create the IOResult,
-//    only when you call it (execute it). This allows you to build complex computations
-//    as pure data structures and defer execution until needed.
+//  1. **Lazy Evaluation**: The side effect doesn't happen when you create the IOResult,
+//     only when you call it (execute it). This allows you to build complex computations
+//     as pure data structures and defer execution until needed.
 //
-//	    // This doesn't read the file yet, just describes how to read it
-//	    readConfig := func() (Config, error) { return os.ReadFile("config.json") }
+//     // This doesn't read the file yet, just describes how to read it
+//     readConfig := func() (Config, error) { return os.ReadFile("config.json") }
 //
-//	    // Still hasn't read the file, just composed operations
-//	    parsed := Map(parseJSON)(readConfig)
+//     // Still hasn't read the file, just composed operations
+//     parsed := Map(parseJSON)(readConfig)
 //
-//	    // NOW it reads the file and parses it
-//	    config, err := parsed()
+//     // NOW it reads the file and parses it
+//     config, err := parsed()
 //
-// 2. **Referential Transparency of the Description**: While the IO operation itself has
-//    side effects, the IOResult value (the function) is referentially transparent. You can
-//    pass it around, compose it, and reason about it without triggering the side effect.
-//    The side effect only occurs when you explicitly call the function.
+//  2. **Referential Transparency of the Description**: While the IO operation itself has
+//     side effects, the IOResult value (the function) is referentially transparent. You can
+//     pass it around, compose it, and reason about it without triggering the side effect.
+//     The side effect only occurs when you explicitly call the function.
 //
 // # Distinguishing Pure from Impure Operations
 //
@@ -135,7 +135,7 @@
 //
 // Transforming values:
 //
-//	doubled := Map(func(x int) int { return x * 2 })(success)
+//	doubled := Map(N.Mul(2))(success)
 //
 // Chaining computations:
 //

v2/idiomatic/ioresult/examples_extract_test.go

@@ -33,7 +33,7 @@ func ExampleIOResult_extraction() {
 
 	// Or more directly using GetOrElse
 	infallibleIO := GetOrElse(F.Constant1[error](io.Of(0)))(someIOResult) // => io returns 42
-	valueFromIO := infallibleIO()                                          // => 42
+	valueFromIO := infallibleIO()                                         // => 42
 
 	fmt.Println(value)
 	fmt.Println(valueFromIO)

v2/idiomatic/ioresult/monad_test.go

@@ -21,6 +21,7 @@ import (
 	"testing"
 
 	F "github.com/IBM/fp-go/v2/function"
+	N "github.com/IBM/fp-go/v2/number"
 	"github.com/stretchr/testify/assert"
 )
 
@@ -78,7 +79,7 @@ func TestFunctorMap(t *testing.T) {
 	t.Run("Maps over successful value", func(t *testing.T) {
 		functor := Functor[int, int]()
 		io := Of(5)
-		mapped := functor.Map(func(x int) int { return x * 2 })(io)
+		mapped := functor.Map(N.Mul(2))(io)
 
 		val, err := mapped()
 		assert.NoError(t, err)
@@ -88,7 +89,7 @@ func TestFunctorMap(t *testing.T) {
 	t.Run("Maps over error preserves error", func(t *testing.T) {
 		functor := Functor[int, int]()
 		io := Left[int](errors.New("test error"))
-		mapped := functor.Map(func(x int) int { return x * 2 })(io)
+		mapped := functor.Map(N.Mul(2))(io)
 
 		_, err := mapped()
 		assert.Error(t, err)
@@ -161,7 +162,7 @@ func TestMonadChain(t *testing.T) {
 func TestMonadAp(t *testing.T) {
 	t.Run("Applies function to value", func(t *testing.T) {
 		monad := Monad[int, int]()
-		fn := Of(func(x int) int { return x * 2 })
+		fn := Of(N.Mul(2))
 		val := monad.Of(5)
 		result := monad.Ap(val)(fn)
 
@@ -183,7 +184,7 @@ func TestMonadAp(t *testing.T) {
 
 	t.Run("Error in value", func(t *testing.T) {
 		monad := Monad[int, int]()
-		fn := Of(func(x int) int { return x * 2 })
+		fn := Of(N.Mul(2))
 		val := Left[int](errors.New("value error"))
 		result := monad.Ap(val)(fn)
 
@@ -423,7 +424,7 @@ func TestFunctorComposition(t *testing.T) {
 		functor2 := Functor[int, string]()
 
 		m := Of(5)
-		f := func(x int) int { return x * 2 }
+		f := N.Mul(2)
 		g := func(x int) string { return fmt.Sprintf("value: %d", x) }
 
 		// Map(g . f)
@@ -444,7 +445,7 @@ func TestFunctorComposition(t *testing.T) {
 		functor2 := Functor[int, string]()
 
 		m := Left[int](errors.New("test error"))
-		f := func(x int) int { return x * 2 }
+		f := N.Mul(2)
 		g := func(x int) string { return fmt.Sprintf("value: %d", x) }
 
 		composed := functor2.Map(F.Flow2(f, g))(m)
@@ -497,7 +498,7 @@ func TestMonadParVsSeq(t *testing.T) {
 		monadSeq := MonadSeq[int, int]()
 
 		io := Of(5)
-		f := func(x int) int { return x * 2 }
+		f := N.Mul(2)
 
 		par := monadPar.Map(f)(io)
 		seq := monadSeq.Map(f)(io)
@@ -533,7 +534,7 @@ func TestMonadParVsSeq(t *testing.T) {
 		monadPar := MonadPar[int, int]()
 
 		io := Of(5)
-		f := func(x int) int { return x * 2 }
+		f := N.Mul(2)
 
 		def := monadDefault.Map(f)(io)
 		par := monadPar.Map(f)(io)
@@ -555,7 +556,7 @@ func TestMonadIntegration(t *testing.T) {
 		// Build a pipeline: multiply by 2, add 3, then format
 		result := F.Pipe2(
 			monad1.Of(5),
-			monad1.Map(func(x int) int { return x * 2 }),
+			monad1.Map(N.Mul(2)),
 			monad1.Chain(func(x int) IOResult[int] {
 				return Of(x + 3)
 			}),
@@ -577,7 +578,7 @@ func TestMonadIntegration(t *testing.T) {
 
 		result := F.Pipe2(
 			monad1.Of(5),
-			monad1.Map(func(x int) int { return x * 2 }),
+			monad1.Map(N.Mul(2)),
 			monad1.Chain(func(x int) IOResult[int] {
 				if x > 5 {
 					return Left[int](errors.New("value too large"))

v2/idiomatic/ioresult/profile_test.go

@@ -20,6 +20,7 @@ import (
 	"testing"
 
 	F "github.com/IBM/fp-go/v2/function"
+	N "github.com/IBM/fp-go/v2/number"
 )
 
 // Benchmark the closure allocations in Bind
@@ -69,7 +70,7 @@ func BenchmarkBindAllocations(b *testing.B) {
 func BenchmarkMapPatterns(b *testing.B) {
 	b.Run("SimpleFunction", func(b *testing.B) {
 		io := Of(42)
-		f := func(x int) int { return x * 2 }
+		f := N.Mul(2)
 
 		b.ResetTimer()
 		b.ReportAllocs()
@@ -85,7 +86,7 @@ func BenchmarkMapPatterns(b *testing.B) {
 		b.ResetTimer()
 		b.ReportAllocs()
 		for i := 0; i < b.N; i++ {
-			result := Map(func(x int) int { return x * 2 })(io)
+			result := Map(N.Mul(2))(io)
 			_, _ = result()
 		}
 	})
@@ -98,9 +99,9 @@ func BenchmarkMapPatterns(b *testing.B) {
 		for i := 0; i < b.N; i++ {
 			result := F.Pipe3(
 				io,
-				Map(func(x int) int { return x + 1 }),
-				Map(func(x int) int { return x * 2 }),
-				Map(func(x int) int { return x - 3 }),
+				Map(N.Add(1)),
+				Map(N.Mul(2)),
+				Map(N.Sub(3)),
 			)
 			_, _ = result()
 		}
@@ -188,7 +189,7 @@ func BenchmarkErrorPaths(b *testing.B) {
 		for i := 0; i < b.N; i++ {
 			result := F.Pipe2(
 				Of(42),
-				Map(func(x int) int { return x * 2 }),
+				Map(N.Mul(2)),
 				Chain(func(x int) IOResult[int] { return Of(x + 1) }),
 			)
 			_, _ = result()
@@ -201,7 +202,7 @@ func BenchmarkErrorPaths(b *testing.B) {
 		for i := 0; i < b.N; i++ {
 			result := F.Pipe2(
 				Left[int](errors.New("error")),
-				Map(func(x int) int { return x * 2 }),
+				Map(N.Mul(2)),
 				Chain(func(x int) IOResult[int] { return Of(x + 1) }),
 			)
 			_, _ = result()

v2/idiomatic/option/benchmark_test.go

@@ -17,6 +17,8 @@ package option
 
 import (
 	"testing"
+
+	N "github.com/IBM/fp-go/v2/number"
 )
 
 // Benchmark basic construction
@@ -46,7 +48,7 @@ func BenchmarkIsSome(b *testing.B) {
 
 func BenchmarkMap(b *testing.B) {
 	v, ok := Some(21)
-	mapper := Map(func(x int) int { return x * 2 })
+	mapper := Map(N.Mul(2))
 	b.ReportAllocs()
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {

v2/idiomatic/option/chain_benchmark_test.go

@@ -17,6 +17,8 @@ package option
 
 import (
 	"testing"
+
+	N "github.com/IBM/fp-go/v2/number"
 )
 
 // Benchmark shallow chain (1 step)
@@ -81,11 +83,11 @@ func BenchmarkMap_5Steps(b *testing.B) {
 	b.ReportAllocs()
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
-		v1, ok1 := Map(func(x int) int { return x + 1 })(v, ok)
-		v2, ok2 := Map(func(x int) int { return x * 3 })(v1, ok1)
-		v3, ok3 := Map(func(x int) int { return x + 20 })(v2, ok2)
-		v4, ok4 := Map(func(x int) int { return x / 2 })(v3, ok3)
-		_, _ = Map(func(x int) int { return x - 10 })(v4, ok4)
+		v1, ok1 := Map(N.Add(1))(v, ok)
+		v2, ok2 := Map(N.Mul(3))(v1, ok1)
+		v3, ok3 := Map(N.Add(20))(v2, ok2)
+		v4, ok4 := Map(N.Div(2))(v3, ok3)
+		_, _ = Map(N.Sub(10))(v4, ok4)
 	}
 }
 

v2/idiomatic/option/doc.go

@@ -58,7 +58,7 @@
 //
 // Map transforms the contained value:
 //
-//	double := Map(func(x int) int { return x * 2 })
+//	double := Map(N.Mul(2))
 //	result := double(Some(21))  // (42, true)
 //	result := double(None[int]())  // (0, false)
 //
@@ -113,7 +113,7 @@
 //
 // Applicative example:
 //
-//	fab := Some(func(x int) int { return x * 2 })
+//	fab := Some(N.Mul(2))
 //	fa := Some(21)
 //	result := Ap[int](fa)(fab)  // (42, true)
 //

v2/idiomatic/option/function.go

@@ -1,15 +1,39 @@
+// Copyright (c) 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 option
 
-// Pipe1 takes an initial value t0 and successively applies 1 functions where the input of a function is the return value of the previous function
-// The final return value is the result of the last function application
+// Pipe1 takes an initial value t0 and successively applies 1 function where the input of a function is the return value of the previous function.
+// The final return value is the result of the last function application.
+//
+// Example:
+//
+//	result := Pipe1(42, func(x int) (int, bool) { return x * 2, true }) // (84, true)
 //
 //go:inline
 func Pipe1[F1 ~func(T0) (T1, bool), T0, T1 any](t0 T0, f1 F1) (T1, bool) {
 	return f1(t0)
 }
 
-// Flow1 creates a function that takes an initial value t0 and successively applies 1 functions where the input of a function is the return value of the previous function
-// The final return value is the result of the last function application
+// Flow1 creates a function that takes an initial value t0 and successively applies 1 function where the input of a function is the return value of the previous function.
+// The final return value is the result of the last function application.
+//
+// Example:
+//
+//	double := Flow1(func(x int, ok bool) (int, bool) { return x * 2, ok })
+//	result := double(42, true) // (84, true)
 //
 //go:inline
 func Flow1[F1 ~func(T0, bool) (T1, bool), T0, T1 any](f1 F1) func(T0, bool) (T1, bool) {

v2/idiomatic/option/missing_test.go

@@ -19,6 +19,7 @@ import (
 	"testing"
 
 	"github.com/IBM/fp-go/v2/eq"
+	N "github.com/IBM/fp-go/v2/number"
 	L "github.com/IBM/fp-go/v2/optics/lens"
 	"github.com/stretchr/testify/assert"
 )
@@ -206,13 +207,13 @@ func TestFlow5(t *testing.T) {
 func TestMakeFunctor(t *testing.T) {
 	t.Run("Map with functor", func(t *testing.T) {
 		f := MakeFunctor[int, int]()
-		double := f.Map(func(x int) int { return x * 2 })
+		double := f.Map(N.Mul(2))
 		AssertEq(Some(42))(double(Some(21)))(t)
 	})
 
 	t.Run("Map with None", func(t *testing.T) {
 		f := MakeFunctor[int, int]()
-		double := f.Map(func(x int) int { return x * 2 })
+		double := f.Map(N.Mul(2))
 		AssertEq(None[int]())(double(None[int]()))(t)
 	})
 }

v2/idiomatic/option/option.go

@@ -30,7 +30,7 @@
 //	result, ok := none         // ok == false, result == 0
 //
 //	// Transforming Options
-//	doubled := Map(func(x int) int { return x * 2 })(some)  // (84, true)
+//	doubled := Map(N.Mul(2))(some)  // (84, true)
 package option
 
 import (
@@ -56,16 +56,47 @@ func FromPredicate[A any](pred func(A) bool) Kleisli[A, A] {
 	}
 }
 
+// FromZero returns a function that creates an Option based on whether a value is the zero value.
+// Returns Some if the value is the zero value, None otherwise.
+//
+// Example:
+//
+//	checkZero := FromZero[int]()
+//	result := checkZero(0)  // Some(0)
+//	result := checkZero(5)  // None
+//
 //go:inline
 func FromZero[A comparable]() Kleisli[A, A] {
 	return FromPredicate(P.IsZero[A]())
 }
 
+// FromNonZero returns a function that creates an Option based on whether a value is non-zero.
+// Returns Some if the value is non-zero, None otherwise.
+//
+// Example:
+//
+//	checkNonZero := FromNonZero[int]()
+//	result := checkNonZero(5)  // Some(5)
+//	result := checkNonZero(0)  // None
+//
 //go:inline
 func FromNonZero[A comparable]() Kleisli[A, A] {
 	return FromPredicate(P.IsNonZero[A]())
 }
 
+// FromEq returns a function that creates an Option based on equality with a given value.
+// The returned function takes a value to compare against and returns a Kleisli function.
+//
+// Parameters:
+//   - pred: An equality predicate
+//
+// Example:
+//
+//	import "github.com/IBM/fp-go/v2/eq"
+//	equals42 := FromEq(eq.FromStrictEquals[int]())(42)
+//	result := equals42(42)  // Some(42)
+//	result := equals42(10)  // None
+//
 //go:inline
 func FromEq[A any](pred eq.Eq[A]) func(A) Kleisli[A, A] {
 	return F.Flow2(P.IsEqual(pred), FromPredicate[A])

v2/idiomatic/option/types.go

@@ -1,3 +1,18 @@
+// Copyright (c) 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 option
 
 import (
@@ -7,6 +22,10 @@ import (
 )
 
 type (
-	Seq[T any]          = iter.Seq[T]
+	// Seq is an iterator sequence type alias for working with Go 1.23+ iterators.
+	Seq[T any] = iter.Seq[T]
+
+	// Endomorphism represents a function from type T to type T.
+	// It is commonly used for transformations that preserve the type.
 	Endomorphism[T any] = endomorphism.Endomorphism[T]
 )

v2/idiomatic/readerioresult/doc.go

@@ -0,0 +1,112 @@
+// 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 readerioresult provides a ReaderIOResult monad that combines Reader, IO, and Result monads.
+//
+// A ReaderIOResult[R, A] represents a computation that:
+//   - Depends on an environment of type R (Reader aspect)
+//   - Performs IO operations (IO aspect)
+//   - May fail with an error (Result aspect, which is Either[error, A])
+//
+// This is equivalent to Reader[R, IOResult[A]] or Reader[R, func() (A, error)].
+//
+// # Use Cases
+//
+// ReaderIOResult is particularly useful for:
+//
+//  1. Dependency injection with IO and error handling - pass configuration/services through
+//     computations that perform side effects and may fail
+//  2. Functional IO with context - compose IO operations that depend on environment and may error
+//  3. Testing - easily mock dependencies and IO operations by changing the environment value
+//  4. Resource management - manage resources that depend on configuration
+//
+// # Basic Example
+//
+//	type Config struct {
+//	    DatabaseURL string
+//	    Timeout     time.Duration
+//	}
+//
+//	// Function that needs config, performs IO, and may fail
+//	func fetchUser(id int) readerioresult.ReaderIOResult[Config, User] {
+//	    return func(cfg Config) ioresult.IOResult[User] {
+//	        return func() (User, error) {
+//	            // Use cfg.DatabaseURL and cfg.Timeout to fetch user
+//	            return queryDatabase(cfg.DatabaseURL, id, cfg.Timeout)
+//	        }
+//	    }
+//	}
+//
+//	// Execute by providing the config
+//	cfg := Config{DatabaseURL: "postgres://...", Timeout: 5 * time.Second}
+//	ioResult := fetchUser(42)(cfg)  // Returns IOResult[User]
+//	user, err := ioResult()         // Execute the IO operation
+//
+// # Composition
+//
+// ReaderIOResult provides several ways to compose computations:
+//
+//  1. Map - transform successful values
+//  2. Chain (FlatMap) - sequence dependent IO operations
+//  3. Ap - combine independent IO computations
+//  4. ChainFirst - perform IO for side effects while keeping original value
+//
+// # Example with Composition
+//
+//	type AppContext struct {
+//	    DB    *sql.DB
+//	    Cache Cache
+//	    Log   Logger
+//	}
+//
+//	getUserWithCache := F.Pipe2(
+//	    getFromCache(userID),
+//	    readerioresult.Alt(func() readerioresult.ReaderIOResult[AppContext, User] {
+//	        return F.Pipe2(
+//	            getFromDB(userID),
+//	            readerioresult.ChainFirst(saveToCache),
+//	        )
+//	    }),
+//	)
+//
+//	ctx := AppContext{DB: db, Cache: cache, Log: logger}
+//	user, err := getUserWithCache(ctx)()
+//
+// # Error Handling
+//
+// ReaderIOResult provides several functions for error handling:
+//
+//   - Left/Right - create failed/successful values
+//   - GetOrElse - provide a default value for errors
+//   - OrElse - recover from errors with an alternative computation
+//   - Fold - handle both success and failure cases
+//   - ChainLeft - transform error values into new computations
+//
+// # Relationship to Other Monads
+//
+// ReaderIOResult is related to several other monads in this library:
+//
+//   - Reader[R, A] - ReaderIOResult without IO or error handling
+//   - IOResult[A] - ReaderIOResult without environment dependency
+//   - ReaderResult[R, A] - ReaderIOResult without IO (pure computations)
+//   - ReaderIO[R, A] - ReaderIOResult without error handling
+//   - ReaderIOEither[R, E, A] - like ReaderIOResult but with custom error type E
+//
+// # Performance Note
+//
+// ReaderIOResult is a zero-cost abstraction - it compiles to a simple function type
+// with no runtime overhead beyond the underlying computation. The IO operations are
+// lazy and only executed when the final IOResult is called.
+package readerioresult

v2/idiomatic/readerioresult/types.go

@@ -27,18 +27,40 @@ import (
 )
 
 type (
+	// Endomorphism represents a function from type A to type A.
 	Endomorphism[A any] = endomorphism.Endomorphism[A]
-	Lazy[A any]         = lazy.Lazy[A]
-	Option[A any]       = option.Option[A]
-	Result[A any]       = result.Result[A]
-	Reader[R, A any]    = reader.Reader[R, A]
-	IO[A any]           = io.IO[A]
-	IOResult[A any]     = ioresult.IOResult[A]
 
+	// Lazy represents a deferred computation that produces a value of type A when evaluated.
+	Lazy[A any] = lazy.Lazy[A]
+
+	// Option represents an optional value that may or may not be present.
+	Option[A any] = option.Option[A]
+
+	// Result represents an Either with error as the left type, compatible with Go's (value, error) tuple.
+	Result[A any] = result.Result[A]
+
+	// Reader represents a computation that depends on a read-only environment of type R and produces a value of type A.
+	Reader[R, A any] = reader.Reader[R, A]
+
+	// IO represents a computation that performs side effects and returns a value of type A.
+	IO[A any] = io.IO[A]
+
+	// IOResult represents a computation that performs IO and may fail with an error.
+	IOResult[A any] = ioresult.IOResult[A]
+
+	// ReaderIOResult represents a computation that depends on an environment R,
+	// performs IO operations, and may fail with an error.
+	// It is equivalent to Reader[R, IOResult[A]] or func(R) func() (A, error).
 	ReaderIOResult[R, A any] = Reader[R, IOResult[A]]
 
+	// Monoid represents a monoid structure for ReaderIOResult values.
 	Monoid[R, A any] = monoid.Monoid[ReaderIOResult[R, A]]
 
-	Kleisli[R, A, B any]  = Reader[A, ReaderIOResult[R, B]]
+	// Kleisli represents a function from A to a ReaderIOResult of B.
+	// It is used for chaining computations that depend on environment, perform IO, and may fail.
+	Kleisli[R, A, B any] = Reader[A, ReaderIOResult[R, B]]
+
+	// Operator represents a transformation from ReaderIOResult[R, A] to ReaderIOResult[R, B].
+	// It is commonly used in function composition pipelines.
 	Operator[R, A, B any] = Kleisli[R, ReaderIOResult[R, A], B]
 )

v2/idiomatic/readerresult/benchmark_test.go

@@ -20,6 +20,7 @@ import (
 	"testing"
 
 	F "github.com/IBM/fp-go/v2/function"
+	N "github.com/IBM/fp-go/v2/number"
 )
 
 type BenchContext struct {
@@ -50,7 +51,7 @@ func BenchmarkLeft(b *testing.B) {
 func BenchmarkMap(b *testing.B) {
 	ctx := BenchContext{Value: 42}
 	rr := Of[BenchContext](10)
-	double := func(x int) int { return x * 2 }
+	double := N.Mul(2)
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
 		mapped := F.Pipe1(rr, Map[BenchContext](double))
@@ -61,7 +62,7 @@ func BenchmarkMap(b *testing.B) {
 func BenchmarkMapChain(b *testing.B) {
 	ctx := BenchContext{Value: 42}
 	rr := Of[BenchContext](1)
-	double := func(x int) int { return x * 2 }
+	double := N.Mul(2)
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
 		result := F.Pipe3(
@@ -109,7 +110,7 @@ func BenchmarkChainDeep(b *testing.B) {
 
 func BenchmarkAp(b *testing.B) {
 	ctx := BenchContext{Value: 42}
-	fab := Of[BenchContext](func(x int) int { return x * 2 })
+	fab := Of[BenchContext](N.Mul(2))
 	fa := Of[BenchContext](21)
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
@@ -188,7 +189,7 @@ func BenchmarkErrorPropagation(b *testing.B) {
 	ctx := BenchContext{Value: 42}
 	err := testError
 	rr := Left[BenchContext, int](err)
-	double := func(x int) int { return x * 2 }
+	double := N.Mul(2)
 
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {

v2/idiomatic/readerresult/bind.go

@@ -17,7 +17,6 @@ package readerresult
 
 import (
 	"github.com/IBM/fp-go/v2/function"
-	F "github.com/IBM/fp-go/v2/function"
 	"github.com/IBM/fp-go/v2/idiomatic/result"
 	AP "github.com/IBM/fp-go/v2/internal/apply"
 	C "github.com/IBM/fp-go/v2/internal/chain"
@@ -69,7 +68,7 @@ func Do[R, S any](
 //	    ConfigService ConfigService
 //	}
 //
-//	result := F.Pipe2(
+//	result := function.Pipe2(
 //	    readereither.Do[Env, error](State{}),
 //	    readereither.Bind(
 //	        func(user User) func(State) State {
@@ -173,7 +172,7 @@ func BindTo[R, S1, T any](
 //	    return env.ConfigService.GetConfig()
 //	})
 //
-//	result := F.Pipe2(
+//	result := function.Pipe2(
 //	    readereither.Do[Env, error](State{}),
 //	    readereither.ApS(
 //	        func(user User) func(State) State {
@@ -228,7 +227,7 @@ func ApS[R, S1, S2, T any](
 //	getConfig := readereither.Asks(func(env Env) either.Either[error, Config] {
 //	    return env.ConfigService.GetConfig()
 //	})
-//	result := F.Pipe2(
+//	result := function.Pipe2(
 //	    readereither.Of[Env, error](State{}),
 //	    readereither.ApSL(configLens, getConfig),
 //	)
@@ -265,7 +264,7 @@ func ApSL[R, S, T any](
 //	    func(s State, u User) State { s.User = u; return s },
 //	)
 //
-//	result := F.Pipe2(
+//	result := function.Pipe2(
 //	    readereither.Do[Env, error](State{}),
 //	    readereither.BindL(userLens, func(user User) readereither.ReaderResult[Env, error, User] {
 //	        return readereither.Asks(func(env Env) either.Either[error, User] {
@@ -279,7 +278,7 @@ func BindL[R, S, T any](
 	lens L.Lens[S, T],
 	f Kleisli[R, T, T],
 ) Operator[R, S, S] {
-	return Bind(lens.Set, F.Flow2(lens.Get, f))
+	return Bind(lens.Set, function.Flow2(lens.Get, f))
 }
 
 // LetL is a variant of Let that uses a lens to focus on a specific part of the context.
@@ -302,7 +301,7 @@ func BindL[R, S, T any](
 //	    func(s State, c Config) State { s.Config = c; return s },
 //	)
 //
-//	result := F.Pipe2(
+//	result := function.Pipe2(
 //	    readereither.Do[any, error](State{Config: Config{Host: "localhost"}}),
 //	    readereither.LetL(configLens, func(cfg Config) Config {
 //	        cfg.Port = 8080
@@ -315,7 +314,7 @@ func LetL[R, S, T any](
 	lens L.Lens[S, T],
 	f Endomorphism[T],
 ) Operator[R, S, S] {
-	return Let[R](lens.Set, F.Flow2(lens.Get, f))
+	return Let[R](lens.Set, function.Flow2(lens.Get, f))
 }
 
 // LetToL is a variant of LetTo that uses a lens to focus on a specific part of the context.
@@ -338,7 +337,7 @@ func LetL[R, S, T any](
 //	)
 //
 //	newConfig := Config{Host: "localhost", Port: 8080}
-//	result := F.Pipe2(
+//	result := function.Pipe2(
 //	    readereither.Do[any, error](State{}),
 //	    readereither.LetToL(configLens, newConfig),
 //	)
@@ -374,7 +373,7 @@ func LetToL[R, S, T any](
 //	    }
 //	}
 //
-//	result := F.Pipe2(
+//	result := function.Pipe2(
 //	    readerresult.Do[Env](State{}),
 //	    readerresult.BindReaderK(
 //	        func(path string) func(State) State {
@@ -435,7 +434,7 @@ func BindEitherK[R, S1, S2, T any](
 //	    return result.Of(s.Value * 2)
 //	}
 //
-//	result := F.Pipe2(
+//	result := function.Pipe2(
 //	    readerresult.Do[any](State{Value: 5}),
 //	    readerresult.BindResultK(
 //	        func(parsed int) func(State) State {
@@ -481,7 +480,7 @@ func BindResultK[R, S1, S2, T any](
 //	    return env.ConfigPath
 //	}
 //
-//	result := F.Pipe1(
+//	result := function.Pipe1(
 //	    reader.Of[Env](getConfigPath),
 //	    readerresult.BindToReader(func(path string) State {
 //	        return State{Config: path}
@@ -530,7 +529,7 @@ func BindToEither[
 //	    return 42
 //	})
 //
-//	computation := F.Pipe1(
+//	computation := function.Pipe1(
 //	    parseResult,
 //	    readerresult.BindToResult[any](func(value int) State {
 //	        return State{Value: value}
@@ -572,7 +571,7 @@ func BindToResult[
 //	getDefaultPort := func(env Env) int { return env.DefaultPort }
 //	getDefaultHost := func(env Env) string { return env.DefaultHost }
 //
-//	result := F.Pipe2(
+//	result := function.Pipe2(
 //	    readerresult.Do[Env](State{}),
 //	    readerresult.ApReaderS(
 //	        func(port int) func(State) State {
@@ -635,7 +634,7 @@ func ApResultS[
 //	parseValue1 := result.TryCatch(func() int { return 42 })
 //	parseValue2 := result.TryCatch(func() int { return 100 })
 //
-//	computation := F.Pipe2(
+//	computation := function.Pipe2(
 //	    readerresult.Do[any](State{}),
 //	    readerresult.ApResultS(
 //	        func(v int) func(State) State {

v2/idiomatic/readerresult/reader.go

@@ -116,7 +116,7 @@ func FromReader[R, A any](r Reader[R, A]) ReaderResult[R, A] {
 // Example:
 //
 //	rr := readerresult.Of[Config](5)
-//	doubled := readerresult.MonadMap(rr, func(x int) int { return x * 2 })
+//	doubled := readerresult.MonadMap(rr, N.Mul(2))
 //	// doubled(cfg) returns (10, nil)
 func MonadMap[R, A, B any](fa ReaderResult[R, A], f func(A) B) ReaderResult[R, B] {
 	mp := result.Map(f)
@@ -130,7 +130,7 @@ func MonadMap[R, A, B any](fa ReaderResult[R, A], f func(A) B) ReaderResult[R, B
 //
 // Example:
 //
-//	double := readerresult.Map[Config](func(x int) int { return x * 2 })
+//	double := readerresult.Map[Config](N.Mul(2))
 //	result := F.Pipe1(readerresult.Of[Config](5), double)
 func Map[R, A, B any](f func(A) B) Operator[R, A, B] {
 	mp := result.Map(f)
@@ -462,7 +462,7 @@ func Flatten[R, A any](mma ReaderResult[R, ReaderResult[R, A]]) ReaderResult[R,
 // Example:
 //
 //	enrichErr := func(e error) error { return fmt.Errorf("enriched: %w", e) }
-//	double := func(x int) int { return x * 2 }
+//	double := N.Mul(2)
 //	result := readerresult.MonadBiMap(rr, enrichErr, double)
 //
 //go:inline
@@ -482,7 +482,7 @@ func MonadBiMap[R, A, B any](fa ReaderResult[R, A], f Endomorphism[error], g fun
 // Example:
 //
 //	enrichErr := func(e error) error { return fmt.Errorf("enriched: %w", e) }
-//	double := func(x int) int { return x * 2 }
+//	double := N.Mul(2)
 //	result := F.Pipe1(rr, readerresult.BiMap[Config](enrichErr, double))
 func BiMap[R, A, B any](f Endomorphism[error], g func(A) B) Operator[R, A, B] {
 	return func(fa ReaderResult[R, A]) ReaderResult[R, B] {
@@ -530,7 +530,7 @@ func Read[A, R any](r R) func(ReaderResult[R, A]) (A, error) {
 //
 // Example:
 //
-//	fabr := readerresult.Of[Config](func(x int) int { return x * 2 })
+//	fabr := readerresult.Of[Config](N.Mul(2))
 //	result := readerresult.MonadFlap(fabr, 5)  // Returns (10, nil)
 //
 //go:inline

v2/idiomatic/readerresult/reader_test.go

@@ -22,6 +22,7 @@ import (
 
 	F "github.com/IBM/fp-go/v2/function"
 	"github.com/IBM/fp-go/v2/internal/utils"
+	N "github.com/IBM/fp-go/v2/number"
 	"github.com/IBM/fp-go/v2/reader"
 	"github.com/IBM/fp-go/v2/result"
 	RES "github.com/IBM/fp-go/v2/result"
@@ -117,7 +118,7 @@ func TestMap(t *testing.T) {
 
 func TestMonadMap(t *testing.T) {
 	rr := Of[MyContext](5)
-	doubled := MonadMap(rr, func(x int) int { return x * 2 })
+	doubled := MonadMap(rr, N.Mul(2))
 	v, err := doubled(defaultContext)
 	assert.NoError(t, err)
 	assert.Equal(t, 10, v)
@@ -341,7 +342,7 @@ func TestFlatten(t *testing.T) {
 
 func TestBiMap(t *testing.T) {
 	enrichErr := func(e error) error { return fmt.Errorf("enriched: %w", e) }
-	double := func(x int) int { return x * 2 }
+	double := N.Mul(2)
 
 	res := F.Pipe1(Of[MyContext](5), BiMap[MyContext](enrichErr, double))
 	v, err := res(defaultContext)
@@ -376,7 +377,7 @@ func TestRead(t *testing.T) {
 }
 
 func TestFlap(t *testing.T) {
-	fabr := Of[MyContext](func(x int) int { return x * 2 })
+	fabr := Of[MyContext](N.Mul(2))
 	flapped := MonadFlap(fabr, 5)
 	v, err := flapped(defaultContext)
 	assert.NoError(t, err)

v2/idiomatic/readerresult/types.go

@@ -26,16 +26,37 @@ import (
 )
 
 type (
+	// Endomorphism represents a function from type A to type A.
 	Endomorphism[A any] = endomorphism.Endomorphism[A]
-	Lazy[A any]         = lazy.Lazy[A]
-	Option[A any]       = option.Option[A]
-	Either[E, A any]    = either.Either[E, A]
-	Result[A any]       = result.Result[A]
-	Reader[R, A any]    = reader.Reader[R, A]
 
+	// Lazy represents a deferred computation that produces a value of type A when evaluated.
+	Lazy[A any] = lazy.Lazy[A]
+
+	// Option represents an optional value that may or may not be present.
+	Option[A any] = option.Option[A]
+
+	// Either represents a value that can be one of two types: Left (E) or Right (A).
+	Either[E, A any] = either.Either[E, A]
+
+	// Result represents an Either with error as the left type, compatible with Go's (value, error) tuple.
+	Result[A any] = result.Result[A]
+
+	// Reader represents a computation that depends on a read-only environment of type R and produces a value of type A.
+	Reader[R, A any] = reader.Reader[R, A]
+
+	// ReaderResult represents a computation that depends on an environment R and may fail with an error.
+	// It is equivalent to Reader[R, Result[A]] or func(R) (A, error).
+	// This combines dependency injection with error handling in a functional style.
 	ReaderResult[R, A any] = func(R) (A, error)
-	Monoid[R, A any]       = monoid.Monoid[ReaderResult[R, A]]
 
-	Kleisli[R, A, B any]  = Reader[A, ReaderResult[R, B]]
+	// Monoid represents a monoid structure for ReaderResult values.
+	Monoid[R, A any] = monoid.Monoid[ReaderResult[R, A]]
+
+	// Kleisli represents a function from A to a ReaderResult of B.
+	// It is used for chaining computations that depend on environment and may fail.
+	Kleisli[R, A, B any] = Reader[A, ReaderResult[R, B]]
+
+	// Operator represents a transformation from ReaderResult[R, A] to ReaderResult[R, B].
+	// It is commonly used in function composition pipelines.
 	Operator[R, A, B any] = Kleisli[R, ReaderResult[R, A], B]
 )

v2/idiomatic/result/examples_extract_test.go

@@ -27,7 +27,7 @@ func Example_extraction() {
 	rightValue, rightErr := Right(10)
 
 	// Convert Either[A] to A with a default value
-	leftWithDefault := GetOrElse(F.Constant1[error](0))(leftValue, leftErr)   // 0
+	leftWithDefault := GetOrElse(F.Constant1[error](0))(leftValue, leftErr)    // 0
 	rightWithDefault := GetOrElse(F.Constant1[error](0))(rightValue, rightErr) // 10
 
 	// Apply a different function on Left(...)/Right(...)

v2/idiomatic/result/function.go

@@ -1,7 +1,26 @@
+// Copyright (c) 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 result
 
-// Pipe1 takes an initial value t0 and successively applies 1 functions where the input of a function is the return value of the previous function
-// The final return value is the result of the last function application
+// Pipe1 takes an initial value t0 and successively applies 1 function where the input of a function is the return value of the previous function.
+// The final return value is the result of the last function application.
+//
+// Example:
+//
+//	result, err := Pipe1(42, func(x int) (int, error) { return x * 2, nil }) // (84, nil)
 //
 //go:inline
 func Pipe1[F1 ~func(T0) (T1, error), T0, T1 any](t0 T0, f1 F1) (T1, error) {

v2/idiomatic/result/validation.go

@@ -67,7 +67,7 @@ import (
 //	})
 //
 //	// ApV with both function and value having errors
-//	double := func(x int) int { return x * 2 }
+//	double := N.Mul(2)
 //	apv := result.ApV[int, int](errorSemigroup)
 //
 //	value := result.Left[int](errors.New("invalid value"))

v2/idiomatic/result/validation_test.go

@@ -21,6 +21,7 @@ import (
 	"strings"
 	"testing"
 
+	N "github.com/IBM/fp-go/v2/number"
 	S "github.com/IBM/fp-go/v2/semigroup"
 	"github.com/stretchr/testify/assert"
 )
@@ -67,7 +68,7 @@ func TestApV_BothRight(t *testing.T) {
 	sg := makeErrorConcatSemigroup()
 	apv := ApV[int, int](sg)
 
-	double := func(x int) int { return x * 2 }
+	double := N.Mul(2)
 
 	value, verr := Right(5)
 	fn, ferr := Right(double)
@@ -83,7 +84,7 @@ func TestApV_ValueLeft_FunctionRight(t *testing.T) {
 	sg := makeErrorConcatSemigroup()
 	apv := ApV[int, int](sg)
 
-	double := func(x int) int { return x * 2 }
+	double := N.Mul(2)
 
 	valueError := errors.New("invalid value")
 	value, verr := Left[int](valueError)
@@ -345,7 +346,7 @@ func BenchmarkApV_BothRight(b *testing.B) {
 	sg := makeErrorConcatSemigroup()
 	apv := ApV[int, int](sg)
 
-	double := func(x int) int { return x * 2 }
+	double := N.Mul(2)
 	value, verr := Right(5)
 	fn, ferr := Right(double)
 

v2/internal/eithert/either.go

@@ -141,6 +141,10 @@ func GetOrElse[E, A, HKTEA, HKTA any](mchain func(HKTEA, func(ET.Either[E, A]) H
 	return MatchE(mchain, onLeft, mof)
 }
 
+func GetOrElseOf[E, A, HKTEA, HKTA any](mchain func(HKTEA, func(ET.Either[E, A]) HKTA) HKTA, mof func(A) HKTA, onLeft func(E) A) func(HKTEA) HKTA {
+	return MatchE(mchain, F.Flow2(onLeft, mof), mof)
+}
+
 func OrElse[E1, E2, A, HKTE1A, HKTE2A any](mchain func(HKTE1A, func(ET.Either[E1, A]) HKTE2A) HKTE2A, mof func(ET.Either[E2, A]) HKTE2A, onLeft func(E1) HKTE2A) func(HKTE1A) HKTE2A {
 	return MatchE(mchain, onLeft, F.Flow2(ET.Right[E2, A], mof))
 }

v2/internal/monad/monad.go

@@ -34,13 +34,16 @@ import (
 // Monads must satisfy the monad laws:
 //
 // Left Identity:
-//   Chain(f)(Of(a)) == f(a)
+//
+//	Chain(f)(Of(a)) == f(a)
 //
 // Right Identity:
-//   Chain(Of)(m) == m
+//
+//	Chain(Of)(m) == m
 //
 // Associativity:
-//   Chain(g)(Chain(f)(m)) == Chain(x => Chain(g)(f(x)))(m)
+//
+//	Chain(g)(Chain(f)(m)) == Chain(x => Chain(g)(f(x)))(m)
 //
 // Type Parameters:
 //   - A: The input value type
@@ -50,20 +53,21 @@ import (
 //   - HKTFAB: The higher-kinded type containing a function from A to B
 //
 // Example:
-//   // Given a Monad for Option
-//   var m Monad[int, string, Option[int], Option[string], Option[func(int) string]]
 //
-//   // Use Of to create a value
-//   value := m.Of(42) // Some(42)
+//	// Given a Monad for Option
+//	var m Monad[int, string, Option[int], Option[string], Option[func(int) string]]
 //
-//   // Use Chain for dependent operations
-//   chainFn := m.Chain(func(x int) Option[string] {
-//     if x > 0 {
-//       return Some(strconv.Itoa(x))
-//     }
-//     return None[string]()
-//   })
-//   result := chainFn(value) // Some("42")
+//	// Use Of to create a value
+//	value := m.Of(42) // Some(42)
+//
+//	// Use Chain for dependent operations
+//	chainFn := m.Chain(func(x int) Option[string] {
+//	  if x > 0 {
+//	    return Some(strconv.Itoa(x))
+//	  }
+//	  return None[string]()
+//	})
+//	result := chainFn(value) // Some("42")
 type Monad[A, B, HKTA, HKTB, HKTFAB any] interface {
 	applicative.Applicative[A, B, HKTA, HKTB, HKTFAB]
 	chain.Chainable[A, B, HKTA, HKTB, HKTFAB]

v2/internal/pointed/types.go

@@ -26,9 +26,10 @@ package pointed
 //   - HKTA: The higher-kinded type containing A (e.g., Option[A], Either[E, A])
 //
 // Example:
-//   // Given a pointed functor for Option[int]
-//   var p Pointed[int, Option[int]]
-//   result := p.Of(42) // Returns Some(42)
+//
+//	// Given a pointed functor for Option[int]
+//	var p Pointed[int, Option[int]]
+//	result := p.Of(42) // Returns Some(42)
 type Pointed[A, HKTA any] interface {
 	// Of lifts a pure value into its higher-kinded type context.
 	//

v2/io/coverage_test.go

@@ -369,7 +369,7 @@ func TestMonadTypeClass(t *testing.T) {
 		m.Chain(func(x int) IO[int] {
 			return m.Of(x * 2)
 		}),
-		m.Map(func(x int) int { return x + 1 }),
+		m.Map(N.Add(1)),
 	)
 
 	assert.Equal(t, 43, result())

v2/io/logging.go

@@ -18,6 +18,10 @@ package io
 import (
 	"fmt"
 	"log"
+	"os"
+	"strings"
+	"sync"
+	"text/template"
 
 	L "github.com/IBM/fp-go/v2/logging"
 )
@@ -32,13 +36,14 @@ import (
 //	    io.ChainFirst(io.Logger[User]()("Fetched user")),
 //	    processUser,
 //	)
-func Logger[A any](loggers ...*log.Logger) func(string) Kleisli[A, any] {
+func Logger[A any](loggers ...*log.Logger) func(string) Kleisli[A, A] {
 	_, right := L.LoggingCallbacks(loggers...)
-	return func(prefix string) Kleisli[A, any] {
-		return func(a A) IO[any] {
-			return FromImpure(func() {
+	return func(prefix string) Kleisli[A, A] {
+		return func(a A) IO[A] {
+			return func() A {
 				right("%s: %v", prefix, a)
-			})
+				return a
+			}
 		}
 	}
 }
@@ -53,11 +58,12 @@ func Logger[A any](loggers ...*log.Logger) func(string) Kleisli[A, any] {
 //	    io.ChainFirst(io.Logf[User]("User: %+v")),
 //	    processUser,
 //	)
-func Logf[A any](prefix string) Kleisli[A, any] {
-	return func(a A) IO[any] {
-		return FromImpure(func() {
+func Logf[A any](prefix string) Kleisli[A, A] {
+	return func(a A) IO[A] {
+		return func() A {
 			log.Printf(prefix, a)
-		})
+			return a
+		}
 	}
 }
 
@@ -72,10 +78,102 @@ func Logf[A any](prefix string) Kleisli[A, any] {
 //	    io.ChainFirst(io.Printf[User]("User: %+v\n")),
 //	    processUser,
 //	)
-func Printf[A any](prefix string) Kleisli[A, any] {
-	return func(a A) IO[any] {
-		return FromImpure(func() {
+func Printf[A any](prefix string) Kleisli[A, A] {
+	return func(a A) IO[A] {
+		return func() A {
 			fmt.Printf(prefix, a)
-		})
+			return a
+		}
 	}
 }
+
+// handleLogging is a helper function that creates a Kleisli arrow for logging/printing
+// values using Go template syntax. It lazily compiles the template on first use and
+// executes it with the provided value as data.
+//
+// Parameters:
+//   - onSuccess: callback function to handle successfully formatted output
+//   - onError: callback function to handle template parsing or execution errors
+//   - prefix: Go template string to format the value
+//
+// The template is compiled lazily using sync.Once to ensure it's only parsed once.
+// The function always returns the original value unchanged, making it suitable for
+// use with ChainFirst or similar operations.
+func handleLogging[A any](onSuccess func(string), onError func(error), prefix string) Kleisli[A, A] {
+	var tmp *template.Template
+	var err error
+	var once sync.Once
+
+	init := func() {
+		tmp, err = template.New("").Parse(prefix)
+	}
+
+	return func(a A) IO[A] {
+		return func() A {
+			// make sure to compile lazily
+			once.Do(init)
+			if err == nil {
+				var buffer strings.Builder
+				tmpErr := tmp.Execute(&buffer, a)
+				if tmpErr != nil {
+					onError(tmpErr)
+					onSuccess(fmt.Sprintf("%v", a))
+				} else {
+					onSuccess(buffer.String())
+				}
+			} else {
+				onError(err)
+				onSuccess(fmt.Sprintf("%v", a))
+			}
+			// in any case return the original value
+			return a
+		}
+	}
+}
+
+// LogGo constructs a logger function using Go template syntax for formatting.
+// The prefix string is parsed as a Go template and executed with the value as data.
+// Both successful output and template errors are logged using log.Println.
+//
+// Example:
+//
+//	type User struct {
+//	    Name string
+//	    Age  int
+//	}
+//	result := pipe.Pipe2(
+//	    fetchUser(),
+//	    io.ChainFirst(io.LogGo[User]("User: {{.Name}}, Age: {{.Age}}")),
+//	    processUser,
+//	)
+func LogGo[A any](prefix string) Kleisli[A, A] {
+	return handleLogging[A](func(value string) {
+		log.Println(value)
+	}, func(err error) {
+		log.Println(err)
+	}, prefix)
+}
+
+// PrintGo constructs a printer function using Go template syntax for formatting.
+// The prefix string is parsed as a Go template and executed with the value as data.
+// Successful output is printed to stdout using fmt.Println, while template errors
+// are printed to stderr using fmt.Fprintln.
+//
+// Example:
+//
+//	type User struct {
+//	    Name string
+//	    Age  int
+//	}
+//	result := pipe.Pipe2(
+//	    fetchUser(),
+//	    io.ChainFirst(io.PrintGo[User]("User: {{.Name}}, Age: {{.Age}}")),
+//	    processUser,
+//	)
+func PrintGo[A any](prefix string) Kleisli[A, A] {
+	return handleLogging[A](func(value string) {
+		fmt.Println(value)
+	}, func(err error) {
+		fmt.Fprintln(os.Stderr, err)
+	}, prefix)
+}

v2/io/logging_test.go

@@ -16,25 +16,206 @@
 package io
 
 import (
+	"bytes"
+	"log"
 	"testing"
 
+	F "github.com/IBM/fp-go/v2/function"
 	"github.com/stretchr/testify/assert"
 )
 
 func TestLogger(t *testing.T) {
-
 	l := Logger[int]()
-
 	lio := l("out")
-
 	assert.NotPanics(t, func() { lio(10)() })
 }
 
+func TestLoggerWithCustomLogger(t *testing.T) {
+	var buf bytes.Buffer
+	customLogger := log.New(&buf, "", 0)
+
+	l := Logger[int](customLogger)
+	lio := l("test value")
+
+	result := lio(42)()
+
+	assert.Equal(t, 42, result)
+	assert.Contains(t, buf.String(), "test value")
+	assert.Contains(t, buf.String(), "42")
+}
+
+func TestLoggerReturnsOriginalValue(t *testing.T) {
+	type TestStruct struct {
+		Name  string
+		Value int
+	}
+
+	l := Logger[TestStruct]()
+	lio := l("test")
+
+	input := TestStruct{Name: "test", Value: 100}
+	result := lio(input)()
+
+	assert.Equal(t, input, result)
+}
+
 func TestLogf(t *testing.T) {
-
 	l := Logf[int]
-
 	lio := l("Value is %d")
-
 	assert.NotPanics(t, func() { lio(10)() })
 }
+
+func TestLogfReturnsOriginalValue(t *testing.T) {
+	l := Logf[string]
+	lio := l("String: %s")
+
+	input := "hello"
+	result := lio(input)()
+
+	assert.Equal(t, input, result)
+}
+
+func TestPrintfLogger(t *testing.T) {
+	l := Printf[int]
+	lio := l("Value: %d\n")
+	assert.NotPanics(t, func() { lio(10)() })
+}
+
+func TestPrintfLoggerReturnsOriginalValue(t *testing.T) {
+	l := Printf[float64]
+	lio := l("Number: %.2f\n")
+
+	input := 3.14159
+	result := lio(input)()
+
+	assert.Equal(t, input, result)
+}
+
+func TestLogGo(t *testing.T) {
+	type User struct {
+		Name string
+		Age  int
+	}
+
+	l := LogGo[User]
+	lio := l("User: {{.Name}}, Age: {{.Age}}")
+
+	input := User{Name: "Alice", Age: 30}
+	assert.NotPanics(t, func() { lio(input)() })
+}
+
+func TestLogGoReturnsOriginalValue(t *testing.T) {
+	type Product struct {
+		ID    int
+		Name  string
+		Price float64
+	}
+
+	l := LogGo[Product]
+	lio := l("Product: {{.Name}} ({{.ID}})")
+
+	input := Product{ID: 123, Name: "Widget", Price: 19.99}
+	result := lio(input)()
+
+	assert.Equal(t, input, result)
+}
+
+func TestLogGoWithInvalidTemplate(t *testing.T) {
+	l := LogGo[int]
+	// Invalid template syntax
+	lio := l("Value: {{.MissingField")
+
+	// Should not panic even with invalid template
+	assert.NotPanics(t, func() { lio(42)() })
+}
+
+func TestLogGoWithComplexTemplate(t *testing.T) {
+	type Address struct {
+		Street string
+		City   string
+	}
+	type Person struct {
+		Name    string
+		Address Address
+	}
+
+	l := LogGo[Person]
+	lio := l("Person: {{.Name}} from {{.Address.City}}")
+
+	input := Person{
+		Name:    "Bob",
+		Address: Address{Street: "Main St", City: "NYC"},
+	}
+	result := lio(input)()
+
+	assert.Equal(t, input, result)
+}
+
+func TestPrintGo(t *testing.T) {
+	type User struct {
+		Name string
+		Age  int
+	}
+
+	l := PrintGo[User]
+	lio := l("User: {{.Name}}, Age: {{.Age}}")
+
+	input := User{Name: "Charlie", Age: 25}
+	assert.NotPanics(t, func() { lio(input)() })
+}
+
+func TestPrintGoReturnsOriginalValue(t *testing.T) {
+	type Score struct {
+		Player string
+		Points int
+	}
+
+	l := PrintGo[Score]
+	lio := l("{{.Player}}: {{.Points}} points")
+
+	input := Score{Player: "Alice", Points: 100}
+	result := lio(input)()
+
+	assert.Equal(t, input, result)
+}
+
+func TestPrintGoWithInvalidTemplate(t *testing.T) {
+	l := PrintGo[string]
+	// Invalid template syntax
+	lio := l("Value: {{.}")
+
+	// Should not panic even with invalid template
+	assert.NotPanics(t, func() { lio("test")() })
+}
+
+func TestLogGoInPipeline(t *testing.T) {
+	type Data struct {
+		Value int
+	}
+
+	input := Data{Value: 10}
+
+	result := F.Pipe2(
+		Of(input),
+		ChainFirst(LogGo[Data]("Processing: {{.Value}}")),
+		Map(func(d Data) Data {
+			return Data{Value: d.Value * 2}
+		}),
+	)()
+
+	assert.Equal(t, 20, result.Value)
+}
+
+func TestPrintGoInPipeline(t *testing.T) {
+	input := "hello"
+
+	result := F.Pipe2(
+		Of(input),
+		ChainFirst(PrintGo[string]("Input: {{.}}")),
+		Map(func(s string) string {
+			return s + " world"
+		}),
+	)()
+
+	assert.Equal(t, "hello world", result)
+}

v2/ioeither/file/file.go

@@ -29,6 +29,48 @@ var (
 	Create = ioeither.Eitherize1(os.Create)
 	// ReadFile reads the context of a file
 	ReadFile = ioeither.Eitherize1(os.ReadFile)
+	// Stat returns [FileInfo] object
+	Stat = ioeither.Eitherize1(os.Stat)
+
+	// UserCacheDir returns an [IOEither] that resolves to the default root directory
+	// to use for user-specific cached data. Users should create their own application-specific
+	// subdirectory within this one and use that.
+	//
+	// On Unix systems, it returns $XDG_CACHE_HOME as specified by
+	// https://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html if
+	// non-empty, else $HOME/.cache.
+	// On Darwin, it returns $HOME/Library/Caches.
+	// On Windows, it returns %LocalAppData%.
+	// On Plan 9, it returns $home/lib/cache.
+	//
+	// If the location cannot be determined (for example, $HOME is not defined),
+	// then it will return an error wrapped in [E.Left].
+	UserCacheDir = ioeither.Eitherize0(os.UserCacheDir)()
+
+	// UserConfigDir returns an [IOEither] that resolves to the default root directory
+	// to use for user-specific configuration data. Users should create their own
+	// application-specific subdirectory within this one and use that.
+	//
+	// On Unix systems, it returns $XDG_CONFIG_HOME as specified by
+	// https://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html if
+	// non-empty, else $HOME/.config.
+	// On Darwin, it returns $HOME/Library/Application Support.
+	// On Windows, it returns %AppData%.
+	// On Plan 9, it returns $home/lib.
+	//
+	// If the location cannot be determined (for example, $HOME is not defined),
+	// then it will return an error wrapped in [E.Left].
+	UserConfigDir = ioeither.Eitherize0(os.UserConfigDir)()
+
+	// UserHomeDir returns an [IOEither] that resolves to the current user's home directory.
+	//
+	// On Unix, including macOS, it returns the $HOME environment variable.
+	// On Windows, it returns %USERPROFILE%.
+	// On Plan 9, it returns the $home environment variable.
+	//
+	// If the location cannot be determined (for example, $HOME is not defined),
+	// then it will return an error wrapped in [E.Left].
+	UserHomeDir = ioeither.Eitherize0(os.UserHomeDir)()
 )
 
 // WriteFile writes a data blob to a file

v2/ioeither/file/read.go

@@ -0,0 +1,80 @@
+// 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 file
+
+import (
+	"io"
+
+	"github.com/IBM/fp-go/v2/ioeither"
+)
+
+// Read uses a generator function to create a stream, reads data from it using a provided
+// reader function, and ensures the stream is properly closed after reading.
+//
+// This function provides safe resource management for reading operations by:
+//  1. Acquiring a ReadCloser resource using the provided acquire function
+//  2. Applying a reader function to extract data from the resource
+//  3. Ensuring the resource is closed, even if an error occurs during reading
+//
+// Type Parameters:
+//   - R: The type of data to be read from the stream
+//   - RD: The type of the ReadCloser resource (must implement io.ReadCloser)
+//
+// Parameters:
+//   - acquire: An IOEither that produces the ReadCloser resource
+//
+// Returns:
+//
+//	A Kleisli function that takes a reader function (which transforms RD to R)
+//	and returns an IOEither that produces the read result R or an error.
+//
+// Example:
+//
+//	import (
+//	    "os"
+//	    "io"
+//	    F "github.com/IBM/fp-go/v2/function"
+//	    "github.com/IBM/fp-go/v2/ioeither"
+//	    "github.com/IBM/fp-go/v2/ioeither/file"
+//	)
+//
+//	// Read first 10 bytes from a file
+//	readFirst10 := func(f *os.File) ioeither.IOEither[error, []byte] {
+//	    return ioeither.TryCatchError(func() ([]byte, error) {
+//	        buf := make([]byte, 10)
+//	        n, err := f.Read(buf)
+//	        return buf[:n], err
+//	    })
+//	}
+//
+//	result := F.Pipe1(
+//	    file.Open("data.txt"),
+//	    file.Read[[]byte, *os.File],
+//	)(readFirst10)
+//
+//	data, err := result()
+//	if err != nil {
+//	    log.Fatal(err)
+//	}
+//	fmt.Printf("Read: %s\n", data)
+//
+// The Read function ensures that the file is closed even if the reading operation fails,
+// providing safe and composable resource management in a functional style.
+func Read[R any, RD io.ReadCloser](acquire IOEither[error, RD]) Kleisli[error, Kleisli[error, RD, R], R] {
+	return ioeither.WithResource[R](
+		acquire,
+		Close[RD])
+}

v2/ioeither/file/read_test.go

@@ -0,0 +1,354 @@
+// 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 file
+
+import (
+	"errors"
+	"io"
+	"os"
+	"strings"
+	"testing"
+
+	E "github.com/IBM/fp-go/v2/either"
+	F "github.com/IBM/fp-go/v2/function"
+	"github.com/IBM/fp-go/v2/ioeither"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+// mockReadCloser is a mock implementation of io.ReadCloser for testing
+type mockReadCloser struct {
+	data        []byte
+	readErr     error
+	closeErr    error
+	readPos     int
+	closeCalled bool
+}
+
+func (m *mockReadCloser) Read(p []byte) (n int, err error) {
+	if m.readErr != nil {
+		return 0, m.readErr
+	}
+	if m.readPos >= len(m.data) {
+		return 0, io.EOF
+	}
+	n = copy(p, m.data[m.readPos:])
+	m.readPos += n
+	if m.readPos >= len(m.data) {
+		return n, io.EOF
+	}
+	return n, nil
+}
+
+func (m *mockReadCloser) Close() error {
+	m.closeCalled = true
+	return m.closeErr
+}
+
+// TestReadSuccessfulRead tests reading data successfully from a ReadCloser
+func TestReadSuccessfulRead(t *testing.T) {
+	testData := []byte("Hello, World!")
+	mock := &mockReadCloser{data: testData}
+
+	// Create an acquire function that returns our mock
+	acquire := ioeither.Of[error](mock)
+
+	// Create a reader function that reads all data
+	reader := func(rc *mockReadCloser) IOEither[error, []byte] {
+		return ioeither.TryCatchError(func() ([]byte, error) {
+			return io.ReadAll(rc)
+		})
+	}
+
+	// Execute the Read operation
+	result := Read[[]byte](acquire)(reader)
+	either := result()
+
+	// Assertions
+	assert.True(t, E.IsRight(either))
+	data := E.GetOrElse(func(error) []byte { return nil })(either)
+	assert.Equal(t, testData, data)
+	assert.True(t, mock.closeCalled, "Close should have been called")
+}
+
+// TestReadWithRealFile tests reading from an actual file
+func TestReadWithRealFile(t *testing.T) {
+	// Create a temporary file
+	tmpFile, err := os.CreateTemp("", "read_test_*.txt")
+	require.NoError(t, err)
+	defer os.Remove(tmpFile.Name())
+
+	testContent := []byte("Test file content for Read function")
+	_, err = tmpFile.Write(testContent)
+	require.NoError(t, err)
+	tmpFile.Close()
+
+	// Use Read to read the file
+	reader := func(f *os.File) IOEither[error, []byte] {
+		return ioeither.TryCatchError(func() ([]byte, error) {
+			return io.ReadAll(f)
+		})
+	}
+
+	result := Read[[]byte](Open(tmpFile.Name()))(reader)
+	either := result()
+
+	assert.True(t, E.IsRight(either))
+	data := E.GetOrElse(func(error) []byte { return nil })(either)
+	assert.Equal(t, testContent, data)
+}
+
+// TestReadPartialRead tests reading only part of the data
+func TestReadPartialRead(t *testing.T) {
+	testData := []byte("Hello, World! This is a longer message.")
+	mock := &mockReadCloser{data: testData}
+
+	acquire := ioeither.Of[error](mock)
+
+	// Reader that only reads first 13 bytes
+	reader := func(rc *mockReadCloser) IOEither[error, []byte] {
+		return ioeither.TryCatchError(func() ([]byte, error) {
+			buf := make([]byte, 13)
+			n, err := rc.Read(buf)
+			if err != nil && err != io.EOF {
+				return nil, err
+			}
+			return buf[:n], nil
+		})
+	}
+
+	result := Read[[]byte](acquire)(reader)
+	either := result()
+
+	assert.True(t, E.IsRight(either))
+	data := E.GetOrElse(func(error) []byte { return nil })(either)
+	assert.Equal(t, []byte("Hello, World!"), data)
+	assert.True(t, mock.closeCalled, "Close should have been called")
+}
+
+// TestReadErrorDuringRead tests that errors during reading are propagated
+func TestReadErrorDuringRead(t *testing.T) {
+	readError := errors.New("read error")
+	mock := &mockReadCloser{
+		data:    []byte("data"),
+		readErr: readError,
+	}
+
+	acquire := ioeither.Of[error](mock)
+
+	reader := func(rc *mockReadCloser) IOEither[error, []byte] {
+		return ioeither.TryCatchError(func() ([]byte, error) {
+			return io.ReadAll(rc)
+		})
+	}
+
+	result := Read[[]byte](acquire)(reader)
+	either := result()
+
+	assert.True(t, E.IsLeft(either))
+	err := E.Fold(func(e error) error { return e }, func([]byte) error { return nil })(either)
+	assert.Equal(t, readError, err)
+	assert.True(t, mock.closeCalled, "Close should be called even on read error")
+}
+
+// TestReadErrorDuringClose tests that errors during close are handled
+func TestReadErrorDuringClose(t *testing.T) {
+	closeError := errors.New("close error")
+	mock := &mockReadCloser{
+		data:     []byte("Hello"),
+		closeErr: closeError,
+	}
+
+	acquire := ioeither.Of[error](mock)
+
+	reader := func(rc *mockReadCloser) IOEither[error, []byte] {
+		return ioeither.TryCatchError(func() ([]byte, error) {
+			return io.ReadAll(rc)
+		})
+	}
+
+	result := Read[[]byte](acquire)(reader)
+	either := result()
+
+	// The close error should be propagated
+	assert.True(t, E.IsLeft(either))
+	assert.True(t, mock.closeCalled, "Close should have been called")
+}
+
+// TestReadErrorDuringAcquire tests that errors during resource acquisition are propagated
+func TestReadErrorDuringAcquire(t *testing.T) {
+	acquireError := errors.New("acquire error")
+	acquire := ioeither.Left[*mockReadCloser](acquireError)
+
+	reader := func(rc *mockReadCloser) IOEither[error, []byte] {
+		return ioeither.TryCatchError(func() ([]byte, error) {
+			return io.ReadAll(rc)
+		})
+	}
+
+	result := Read[[]byte](acquire)(reader)
+	either := result()
+
+	assert.True(t, E.IsLeft(either))
+	err := E.Fold(func(e error) error { return e }, func([]byte) error { return nil })(either)
+	assert.Equal(t, acquireError, err)
+}
+
+// TestReadWithStringReader tests reading and transforming to a different type
+func TestReadWithStringReader(t *testing.T) {
+	testData := []byte("Hello, World!")
+	mock := &mockReadCloser{data: testData}
+
+	acquire := ioeither.Of[error](mock)
+
+	// Reader that converts bytes to uppercase string
+	reader := func(rc *mockReadCloser) IOEither[error, string] {
+		return ioeither.TryCatchError(func() (string, error) {
+			data, err := io.ReadAll(rc)
+			if err != nil {
+				return "", err
+			}
+			return strings.ToUpper(string(data)), nil
+		})
+	}
+
+	result := Read[string](acquire)(reader)
+	either := result()
+
+	assert.True(t, E.IsRight(either))
+	str := E.GetOrElse(func(error) string { return "" })(either)
+	assert.Equal(t, "HELLO, WORLD!", str)
+	assert.True(t, mock.closeCalled, "Close should have been called")
+}
+
+// TestReadComposition tests composing Read with other operations
+func TestReadComposition(t *testing.T) {
+	testData := []byte("42")
+	mock := &mockReadCloser{data: testData}
+
+	acquire := ioeither.Of[error](mock)
+
+	// Reader that parses the content as an integer
+	reader := func(rc *mockReadCloser) IOEither[error, int] {
+		return ioeither.TryCatchError(func() (int, error) {
+			data, err := io.ReadAll(rc)
+			if err != nil {
+				return 0, err
+			}
+			var num int
+			// Simple parsing
+			num = int(data[0]-'0')*10 + int(data[1]-'0')
+			return num, nil
+		})
+	}
+
+	result := F.Pipe1(
+		acquire,
+		Read[int],
+	)(reader)
+
+	either := result()
+
+	assert.True(t, E.IsRight(either))
+	num := E.GetOrElse(func(error) int { return 0 })(either)
+	assert.Equal(t, 42, num)
+	assert.True(t, mock.closeCalled, "Close should have been called")
+}
+
+// TestReadMultipleOperations tests that Read can be used multiple times
+func TestReadMultipleOperations(t *testing.T) {
+	// Create a function that creates a new mock each time
+	createMock := func() *mockReadCloser {
+		return &mockReadCloser{data: []byte("test data")}
+	}
+
+	reader := func(rc *mockReadCloser) IOEither[error, []byte] {
+		return ioeither.TryCatchError(func() ([]byte, error) {
+			return io.ReadAll(rc)
+		})
+	}
+
+	// First read
+	mock1 := createMock()
+	result1 := Read[[]byte](ioeither.Of[error](mock1))(reader)
+	either1 := result1()
+
+	assert.True(t, E.IsRight(either1))
+	data1 := E.GetOrElse(func(error) []byte { return nil })(either1)
+	assert.Equal(t, []byte("test data"), data1)
+	assert.True(t, mock1.closeCalled)
+
+	// Second read with a new mock
+	mock2 := createMock()
+	result2 := Read[[]byte](ioeither.Of[error](mock2))(reader)
+	either2 := result2()
+
+	assert.True(t, E.IsRight(either2))
+	data2 := E.GetOrElse(func(error) []byte { return nil })(either2)
+	assert.Equal(t, []byte("test data"), data2)
+	assert.True(t, mock2.closeCalled)
+}
+
+// TestReadEnsuresCloseOnPanic tests that Close is called even if reader panics
+// Note: This is more of a conceptual test as the actual panic handling depends on
+// the implementation of WithResource
+func TestReadWithEmptyData(t *testing.T) {
+	mock := &mockReadCloser{data: []byte{}}
+
+	acquire := ioeither.Of[error](mock)
+
+	reader := func(rc *mockReadCloser) IOEither[error, []byte] {
+		return ioeither.TryCatchError(func() ([]byte, error) {
+			return io.ReadAll(rc)
+		})
+	}
+
+	result := Read[[]byte](acquire)(reader)
+	either := result()
+
+	assert.True(t, E.IsRight(either))
+	data := E.GetOrElse(func(error) []byte { return nil })(either)
+	assert.Empty(t, data)
+	assert.True(t, mock.closeCalled, "Close should be called even with empty data")
+}
+
+// TestReadIntegrationWithEither tests integration with Either operations
+func TestReadIntegrationWithEither(t *testing.T) {
+	testData := []byte("integration test")
+	mock := &mockReadCloser{data: testData}
+
+	acquire := ioeither.Of[error](mock)
+
+	reader := func(rc *mockReadCloser) IOEither[error, []byte] {
+		return ioeither.TryCatchError(func() ([]byte, error) {
+			return io.ReadAll(rc)
+		})
+	}
+
+	result := Read[[]byte](acquire)(reader)
+	either := result()
+
+	// Test with Either operations
+	assert.True(t, E.IsRight(either))
+
+	folded := E.Fold(
+		func(err error) string { return "error: " + err.Error() },
+		func(data []byte) string { return "success: " + string(data) },
+	)(either)
+
+	assert.Equal(t, "success: integration test", folded)
+	assert.True(t, mock.closeCalled)
+}

v2/ioeither/http/builder/builder_test.go

@@ -31,7 +31,7 @@ import (
 func TestBuilderWithQuery(t *testing.T) {
 	// add some query
 	withLimit := R.WithQueryArg("limit")("10")
-	withURL := R.WithUrl("http://www.example.org?a=b")
+	withURL := R.WithURL("http://www.example.org?a=b")
 
 	b := F.Pipe2(
 		R.Default,

v2/ioeither/ioeither.go

@@ -264,6 +264,11 @@ func GetOrElse[E, A any](onLeft func(E) IO[A]) func(IOEither[E, A]) IO[A] {
 	return eithert.GetOrElse(io.MonadChain[Either[E, A], A], io.MonadOf[A], onLeft)
 }
 
+// GetOrElseOf extracts the value or maps the error
+func GetOrElseOf[E, A any](onLeft func(E) A) func(IOEither[E, A]) IO[A] {
+	return eithert.GetOrElseOf(io.MonadChain[Either[E, A], A], io.MonadOf[A], onLeft)
+}
+
 // MonadChainTo composes to the second monad ignoring the return value of the first
 func MonadChainTo[A, E, B any](fa IOEither[E, A], fb IOEither[E, B]) IOEither[E, B] {
 	return MonadChain(fa, function.Constant1[A](fb))

v2/ioresult/bench_test.go

@@ -19,6 +19,7 @@ import (
 	"testing"
 
 	F "github.com/IBM/fp-go/v2/function"
+	N "github.com/IBM/fp-go/v2/number"
 )
 
 func BenchmarkOf(b *testing.B) {
@@ -29,7 +30,7 @@ func BenchmarkOf(b *testing.B) {
 
 func BenchmarkMap(b *testing.B) {
 	io := Of(42)
-	f := func(x int) int { return x * 2 }
+	f := N.Mul(2)
 
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
@@ -68,9 +69,9 @@ func BenchmarkBind(b *testing.B) {
 }
 
 func BenchmarkPipeline(b *testing.B) {
-	f1 := func(x int) int { return x + 1 }
-	f2 := func(x int) int { return x * 2 }
-	f3 := func(x int) int { return x - 3 }
+	f1 := N.Add(1)
+	f2 := N.Mul(2)
+	f3 := N.Sub(3)
 
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
@@ -93,9 +94,9 @@ func BenchmarkExecute(b *testing.B) {
 }
 
 func BenchmarkExecutePipeline(b *testing.B) {
-	f1 := func(x int) int { return x + 1 }
-	f2 := func(x int) int { return x * 2 }
-	f3 := func(x int) int { return x - 3 }
+	f1 := N.Add(1)
+	f2 := N.Mul(2)
+	f3 := N.Sub(3)
 
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {

v2/ioresult/file/file.go

@@ -29,6 +29,48 @@ var (
 	Create = file.Create
 	// ReadFile reads the context of a file
 	ReadFile = file.ReadFile
+	// Stat returns [FileInfo] object
+	Stat = file.Stat
+
+	// UserCacheDir returns an [IOResult] that resolves to the default root directory
+	// to use for user-specific cached data. Users should create their own application-specific
+	// subdirectory within this one and use that.
+	//
+	// On Unix systems, it returns $XDG_CACHE_HOME as specified by
+	// https://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html if
+	// non-empty, else $HOME/.cache.
+	// On Darwin, it returns $HOME/Library/Caches.
+	// On Windows, it returns %LocalAppData%.
+	// On Plan 9, it returns $home/lib/cache.
+	//
+	// If the location cannot be determined (for example, $HOME is not defined),
+	// then it will return an error wrapped in [Err].
+	UserCacheDir = file.UserCacheDir
+
+	// UserConfigDir returns an [IOResult] that resolves to the default root directory
+	// to use for user-specific configuration data. Users should create their own
+	// application-specific subdirectory within this one and use that.
+	//
+	// On Unix systems, it returns $XDG_CONFIG_HOME as specified by
+	// https://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html if
+	// non-empty, else $HOME/.config.
+	// On Darwin, it returns $HOME/Library/Application Support.
+	// On Windows, it returns %AppData%.
+	// On Plan 9, it returns $home/lib.
+	//
+	// If the location cannot be determined (for example, $HOME is not defined),
+	// then it will return an error wrapped in [Err].
+	UserConfigDir = file.UserConfigDir
+
+	// UserHomeDir returns an [IOResult] that resolves to the current user's home directory.
+	//
+	// On Unix, including macOS, it returns the $HOME environment variable.
+	// On Windows, it returns %USERPROFILE%.
+	// On Plan 9, it returns the $home environment variable.
+	//
+	// If the location cannot be determined (for example, $HOME is not defined),
+	// then it will return an error wrapped in [Err].
+	UserHomeDir = file.UserHomeDir
 )
 
 // WriteFile writes a data blob to a file

v2/ioresult/file/read.go

@@ -0,0 +1,111 @@
+// 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 file
+
+import (
+	"io"
+
+	"github.com/IBM/fp-go/v2/ioeither/file"
+)
+
+// Read uses a generator function to create a stream, reads data from it using a provided
+// reader function, and ensures the stream is properly closed after reading.
+//
+// This function provides safe resource management for reading operations by:
+//  1. Acquiring a ReadCloser resource using the provided acquire function
+//  2. Applying a reader function to extract data from the resource
+//  3. Ensuring the resource is closed, even if an error occurs during reading
+//
+// Type Parameters:
+//   - R: The type of data to be read from the stream
+//   - RD: The type of the ReadCloser resource (must implement io.ReadCloser)
+//
+// Parameters:
+//   - acquire: An IOResult that produces the ReadCloser resource
+//
+// Returns:
+//
+//	A Kleisli function that takes a reader function (which transforms RD to R)
+//	and returns an IOResult that produces the read result R or an error.
+//
+// The key difference from ioeither.Read is that this returns IOResult[R] which is
+// IO[Result[R]], representing a computation that returns a Result type (tuple of value and error)
+// rather than an Either type.
+//
+// Example - Reading first N bytes from a file:
+//
+//	import (
+//	    "os"
+//	    "io"
+//	    F "github.com/IBM/fp-go/v2/function"
+//	    R "github.com/IBM/fp-go/v2/result"
+//	    "github.com/IBM/fp-go/v2/ioresult"
+//	    "github.com/IBM/fp-go/v2/ioresult/file"
+//	)
+//
+//	// Read first 10 bytes from a file
+//	readFirst10 := func(f *os.File) ioresult.IOResult[[]byte] {
+//	    return ioresult.TryCatch(func() ([]byte, error) {
+//	        buf := make([]byte, 10)
+//	        n, err := f.Read(buf)
+//	        return buf[:n], err
+//	    })
+//	}
+//
+//	result := F.Pipe1(
+//	    file.Open("data.txt"),
+//	    file.Read[[]byte, *os.File],
+//	)(readFirst10)
+//
+//	// Execute the IO operation to get the Result
+//	res := result()
+//	data, err := res()  // Result is a tuple function
+//	if err != nil {
+//	    log.Fatal(err)
+//	}
+//	fmt.Printf("Read: %s\n", data)
+//
+// Example - Using with Result combinators:
+//
+//	result := F.Pipe1(
+//	    file.Open("config.json"),
+//	    file.Read[[]byte, *os.File],
+//	)(readFirst10)
+//
+//	// Chain operations using Result combinators
+//	processed := F.Pipe2(
+//	    result,
+//	    ioresult.Map(func(data []byte) string {
+//	        return string(data)
+//	    }),
+//	    ioresult.ChainFirst(func(s string) ioresult.IOResult[any] {
+//	        return ioresult.Of[any](fmt.Printf("Read: %s\n", s))
+//	    }),
+//	)
+//
+//	res := processed()
+//	str, err := res()
+//	if err != nil {
+//	    log.Fatal(err)
+//	}
+//
+// The Read function ensures that the file is closed even if the reading operation fails,
+// providing safe and composable resource management in a functional style.
+//
+//go:inline
+func Read[R any, RD io.ReadCloser](acquire IOResult[RD]) Kleisli[Kleisli[RD, R], R] {
+	return file.Read[R](acquire)
+}

v2/ioresult/file/read_example_test.go

@@ -0,0 +1,64 @@
+// 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 file_test
+
+import (
+	"fmt"
+	"io"
+	"os"
+
+	FL "github.com/IBM/fp-go/v2/file"
+	F "github.com/IBM/fp-go/v2/function"
+	I "github.com/IBM/fp-go/v2/io"
+	"github.com/IBM/fp-go/v2/ioresult"
+	"github.com/IBM/fp-go/v2/ioresult/file"
+)
+
+// Example_read_basicUsage demonstrates basic usage of the Read function
+// to read data from a file with automatic resource cleanup.
+func Example_read_basicUsage() {
+	// Create a temporary file for demonstration
+	tmpFile, err := os.CreateTemp("", "example-*.txt")
+	if err != nil {
+		fmt.Printf("Error creating temp file: %v\n", err)
+		return
+	}
+	defer os.Remove(tmpFile.Name())
+
+	// Write some test data
+	testData := "Hello, World! This is a test file."
+	if _, err := tmpFile.WriteString(testData); err != nil {
+		fmt.Printf("Error writing to temp file: %v\n", err)
+		return
+	}
+	tmpFile.Close()
+
+	// Define a reader function that reads the full file content
+	readAll := F.Flow2(
+		FL.ToReader[*os.File],
+		ioresult.Eitherize1(io.ReadAll),
+	)
+
+	content := F.Pipe2(
+		readAll,
+		file.Read[[]byte](file.Open(tmpFile.Name())),
+		ioresult.TapIOK(I.Printf[[]byte]("%s\n")),
+	)
+
+	content()
+
+	// Output: Hello, World! This is a test file.
+}

v2/ioresult/file/tempfile.go

@@ -22,11 +22,110 @@ import (
 )
 
 var (
-	// CreateTemp created a temp file with proper parametrization
+	// CreateTemp creates a temporary file with proper parametrization.
+	// It is an alias for ioeither.file.CreateTemp which wraps os.CreateTemp
+	// in an IOResult context for functional composition.
+	//
+	// This function takes a directory and pattern parameter and returns an IOResult
+	// that produces a temporary file handle when executed.
+	//
+	// Parameters:
+	//   - dir: directory where the temporary file should be created (empty string uses default temp dir)
+	//   - pattern: filename pattern with optional '*' placeholder for random suffix
+	//
+	// Returns:
+	//   IOResult[*os.File] that when executed creates and returns a temporary file handle
+	//
+	// Example:
+	//   tempFile := CreateTemp("", "myapp-*.tmp")
+	//   result := tempFile()
+	//   file, err := E.UnwrapError(result)
+	//   if err != nil {
+	//       log.Fatal(err)
+	//   }
+	//   defer file.Close()
 	CreateTemp = file.CreateTemp
 )
 
-// WithTempFile creates a temporary filthen invokes a callback to create a resource based on the filthen close and remove the temp file
+// WithTempFile creates a temporary file, then invokes a callback to create a resource
+// based on the file, then automatically closes and removes the temp file.
+//
+// This function provides safe temporary file management by:
+//  1. Creating a temporary file with sensible defaults
+//  2. Passing the file handle to the provided callback function
+//  3. Ensuring the file is closed and removed, even if the callback fails
+//
+// Type Parameters:
+//   - A: The type of result produced by the callback function
+//
+// Parameters:
+//   - f: A Kleisli function that takes a *os.File and returns an IOResult[A]
+//
+// Returns:
+//
+//	IOResult[A] that when executed creates a temp file, runs the callback,
+//	and cleans up the file regardless of success or failure
+//
+// Example - Writing and reading from a temporary file:
+//
+//	import (
+//	    "io"
+//	    "os"
+//	    E "github.com/IBM/fp-go/v2/either"
+//	    "github.com/IBM/fp-go/v2/ioresult"
+//	    "github.com/IBM/fp-go/v2/ioresult/file"
+//	)
+//
+//	// Write data to temp file and return the number of bytes written
+//	writeToTemp := func(f *os.File) ioresult.IOResult[int] {
+//	    return ioresult.TryCatchError(func() (int, error) {
+//	        data := []byte("Hello, temporary world!")
+//	        return f.Write(data)
+//	    })
+//	}
+//
+//	result := file.WithTempFile(writeToTemp)
+//	bytesWritten, err := E.UnwrapError(result())
+//	if err != nil {
+//	    log.Fatal(err)
+//	}
+//	fmt.Printf("Wrote %d bytes to temporary file\n", bytesWritten)
+//
+// Example - Processing data through a temporary file:
+//
+//	processData := func(data []byte) ioresult.IOResult[string] {
+//	    return file.WithTempFile(func(f *os.File) ioresult.IOResult[string] {
+//	        return ioresult.TryCatchError(func() (string, error) {
+//	            // Write data to temp file
+//	            if _, err := f.Write(data); err != nil {
+//	                return "", err
+//	            }
+//
+//	            // Seek back to beginning
+//	            if _, err := f.Seek(0, 0); err != nil {
+//	                return "", err
+//	            }
+//
+//	            // Read and process
+//	            processed, err := io.ReadAll(f)
+//	            if err != nil {
+//	                return "", err
+//	            }
+//
+//	            return strings.ToUpper(string(processed)), nil
+//	        })
+//	    })
+//	}
+//
+//	result := processData([]byte("hello world"))
+//	output, err := E.UnwrapError(result())
+//	if err != nil {
+//	    log.Fatal(err)
+//	}
+//	fmt.Println(output) // "HELLO WORLD"
+//
+// The temporary file is guaranteed to be cleaned up even if the callback function
+// panics or returns an error, providing safe resource management in a functional style.
 //
 //go:inline
 func WithTempFile[A any](f Kleisli[*os.File, A]) IOResult[A] {

v2/ioresult/file/tempfile_test.go

@@ -32,7 +32,6 @@ func TestCreateTemp(t *testing.T) {
 
 		assert.NoError(t, err)
 
-
 		assert.NotNil(t, file)
 
 		tmpPath := file.Name()
@@ -49,7 +48,6 @@ func TestCreateTemp(t *testing.T) {
 
 		assert.NoError(t, err)
 
-
 		assert.NotNil(t, file)
 
 		tmpPath := file.Name()
@@ -68,7 +66,6 @@ func TestCreateTemp(t *testing.T) {
 
 		assert.NoError(t, err)
 
-
 		assert.NotNil(t, file)
 
 		tmpPath := file.Name()
@@ -95,7 +92,6 @@ func TestWithTempFile(t *testing.T) {
 
 		assert.NoError(t, err)
 
-
 		assert.Equal(t, testData, returnedData)
 	})
 
@@ -115,7 +111,6 @@ func TestWithTempFile(t *testing.T) {
 
 		assert.NoError(t, err)
 
-
 		assert.Equal(t, tmpPath, path)
 
 		_, statErr := os.Stat(tmpPath)
@@ -165,7 +160,6 @@ func TestWithTempFile(t *testing.T) {
 
 		assert.NoError(t, err)
 
-
 		assert.Equal(t, testContent, content)
 	})
 
@@ -182,9 +176,8 @@ func TestWithTempFile(t *testing.T) {
 			result := WithTempFile(useFile)()
 			path, err := E.UnwrapError(result)
 
-		assert.NoError(t, err)
+			assert.NoError(t, err)
 
-	
 			paths = append(paths, path)
 		}
 
@@ -239,7 +232,6 @@ func TestWithTempFile(t *testing.T) {
 
 		assert.NoError(t, err)
 
-
 		assert.Equal(t, testData, returnedData)
 	})
 

v2/ioresult/file/types.go

@@ -1,9 +1,88 @@
+// 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 file
 
 import "github.com/IBM/fp-go/v2/ioresult"
 
 type (
-	IOResult[T any]    = ioresult.IOResult[T]
-	Kleisli[A, B any]  = ioresult.Kleisli[A, B]
+	// IOResult represents a synchronous computation that may fail, returning a Result type.
+	// It is an alias for ioresult.IOResult[T] which is equivalent to IO[Result[T]].
+	//
+	// IOResult[T] is a function that when executed returns Result[T], which is Either[error, T].
+	// This provides a functional approach to handling IO operations that may fail, with
+	// automatic resource management and composable error handling.
+	//
+	// Example:
+	//   var readFile IOResult[[]byte] = func() Result[[]byte] {
+	//       data, err := os.ReadFile("config.json")
+	//       return result.TryCatchError(data, err)
+	//   }
+	//
+	//   // Execute the IO operation
+	//   result := readFile()
+	//   data, err := E.UnwrapError(result)
+	IOResult[T any] = ioresult.IOResult[T]
+
+	// Kleisli represents a function that takes a value of type A and returns an IOResult[B].
+	// It is an alias for ioresult.Kleisli[A, B] which is equivalent to Reader[A, IOResult[B]].
+	//
+	// Kleisli functions are the building blocks of monadic composition in the IOResult context.
+	// They allow for chaining operations that may fail while maintaining functional purity.
+	//
+	// Example:
+	//   // A Kleisli function that reads from a file handle
+	//   var readAll Kleisli[*os.File, []byte] = func(f *os.File) IOResult[[]byte] {
+	//       return TryCatchError(func() ([]byte, error) {
+	//           return io.ReadAll(f)
+	//       })
+	//   }
+	//
+	//   // Can be composed with other Kleisli functions
+	//   var processFile = F.Pipe1(
+	//       file.Open("data.txt"),
+	//       file.Read[[]byte, *os.File],
+	//   )(readAll)
+	Kleisli[A, B any] = ioresult.Kleisli[A, B]
+
+	// Operator represents a function that transforms one IOResult into another.
+	// It is an alias for ioresult.Operator[A, B] which is equivalent to Kleisli[IOResult[A], B].
+	//
+	// Operators are used for transforming and composing IOResult values, providing a way
+	// to build complex data processing pipelines while maintaining error handling semantics.
+	//
+	// Example:
+	//   // An operator that converts bytes to string
+	//   var bytesToString Operator[[]byte, string] = Map(func(data []byte) string {
+	//       return string(data)
+	//   })
+	//
+	//   // An operator that validates JSON
+	//   var validateJSON Operator[string, map[string]interface{}] = ChainEitherK(
+	//       func(s string) Result[map[string]interface{}] {
+	//           var result map[string]interface{}
+	//           err := json.Unmarshal([]byte(s), &result)
+	//           return result.TryCatchError(result, err)
+	//       },
+	//   )
+	//
+	//   // Compose operators in a pipeline
+	//   var processJSON = F.Pipe2(
+	//       readFileOperation,
+	//       bytesToString,
+	//       validateJSON,
+	//   )
 	Operator[A, B any] = ioresult.Operator[A, B]
 )

v2/ioresult/ioeither.go

@@ -286,6 +286,11 @@ func GetOrElse[A any](onLeft func(error) IO[A]) func(IOResult[A]) IO[A] {
 	return ioeither.GetOrElse(onLeft)
 }
 
+//go:inline
+func GetOrElseOf[A any](onLeft func(error) A) func(IOResult[A]) IO[A] {
+	return ioeither.GetOrElseOf(onLeft)
+}
+
 // MonadChainTo composes to the second monad ignoring the return value of the first
 //
 //go:inline

v2/iterator/iter/iter.go

@@ -476,7 +476,7 @@ func Flatten[A any](mma Seq[Seq[A]]) Seq[A] {
 //
 // Example:
 //
-//	fns := From(N.Mul(2), func(x int) int { return x + 10 })
+//	fns := From(N.Mul(2), N.Add(10))
 //	vals := From(5, 3)
 //	result := MonadAp(fns, vals)
 //	// yields: 10, 6, 15, 13 (each function applied to each value)
@@ -492,7 +492,7 @@ func MonadAp[B, A any](fab Seq[func(A) B], fa Seq[A]) Seq[B] {
 // Example:
 //
 //	applyTo5 := Ap(From(5))
-//	fns := From(N.Mul(2), func(x int) int { return x + 10 })
+//	fns := From(N.Mul(2), N.Add(10))
 //	result := applyTo5(fns)
 //	// yields: 10, 15
 //
@@ -799,7 +799,7 @@ func FoldMapWithKey[K, A, B any](m M.Monoid[B]) func(func(K, A) B) func(Seq2[K,
 //
 // Example:
 //
-//	fns := From(N.Mul(2), func(x int) int { return x + 10 })
+//	fns := From(N.Mul(2), N.Add(10))
 //	result := MonadFlap(fns, 5)
 //	// yields: 10, 15
 //

v2/iterator/iter/iter_test.go

@@ -251,7 +251,7 @@ func TestFlatten(t *testing.T) {
 func TestMonadAp(t *testing.T) {
 	fns := From(
 		N.Mul(2),
-		func(x int) int { return x + 10 },
+		N.Add(10),
 	)
 	vals := From(1, 2)
 	result := MonadAp(fns, vals)
@@ -261,7 +261,7 @@ func TestMonadAp(t *testing.T) {
 func TestAp(t *testing.T) {
 	fns := From(
 		N.Mul(2),
-		func(x int) int { return x + 10 },
+		N.Add(10),
 	)
 	vals := From(1, 2)
 	applier := Ap[int](vals)
@@ -425,7 +425,7 @@ func TestFoldMapWithKey(t *testing.T) {
 func TestMonadFlap(t *testing.T) {
 	fns := From(
 		N.Mul(2),
-		func(x int) int { return x + 10 },
+		N.Add(10),
 	)
 	result := MonadFlap(fns, 5)
 	assert.Equal(t, []int{10, 15}, toSlice(result))
@@ -434,7 +434,7 @@ func TestMonadFlap(t *testing.T) {
 func TestFlap(t *testing.T) {
 	fns := From(
 		N.Mul(2),
-		func(x int) int { return x + 10 },
+		N.Add(10),
 	)
 	flapper := Flap[int](5)
 	result := toSlice(flapper(fns))
@@ -525,7 +525,7 @@ func TestPipelineComposition(t *testing.T) {
 	result := F.Pipe4(
 		From(1, 2, 3, 4, 5, 6),
 		Filter(func(x int) bool { return x%2 == 0 }),
-		Map(func(x int) int { return x * 10 }),
+		Map(N.Mul(10)),
 		Prepend(0),
 		toSlice[int],
 	)

v2/lazy/lazy_extended_test.go

@@ -496,7 +496,7 @@ func TestMapComposition(t *testing.T) {
 	result := F.Pipe3(
 		Of(5),
 		Map(N.Mul(2)),
-		Map(func(x int) int { return x + 10 }),
+		Map(N.Add(10)),
 		Map(func(x int) int { return x }),
 	)
 

v2/optics/iso/option/isos_test.go

@@ -239,7 +239,7 @@ func TestFromZeroWithCompose(t *testing.T) {
 			return O.MonadMap(opt, N.Mul(2))
 		},
 		func(opt O.Option[int]) O.Option[int] {
-			return O.MonadMap(opt, func(x int) int { return x / 2 })
+			return O.MonadMap(opt, N.Div(2))
 		},
 	)
 

v2/optics/lens/lens.go

@@ -17,6 +17,8 @@
 package lens
 
 import (
+	"fmt"
+
 	"github.com/IBM/fp-go/v2/endomorphism"
 	EQ "github.com/IBM/fp-go/v2/eq"
 	F "github.com/IBM/fp-go/v2/function"
@@ -597,3 +599,11 @@ func IMap[S any, AB ~func(A) B, BA ~func(B) A, A, B any](ab AB, ba BA) Operator[
 		return MakeLensCurried(F.Flow2(ea.Get, ab), F.Flow2(ba, ea.Set))
 	}
 }
+
+func (l Lens[S, T]) String() string {
+	return "Lens"
+}
+
+func (l Lens[S, T]) Format(f fmt.State, c rune) {
+	fmt.Fprint(f, l.String())
+}

v2/optics/lens/lens_laws_test.go

@@ -557,7 +557,7 @@ func TestModifyLaws(t *testing.T) {
 	// Modify composition: Modify(f ∘ g) = Modify(f) ∘ Modify(g)
 	t.Run("ModifyComposition", func(t *testing.T) {
 		f := N.Mul(2)
-		g := func(x int) int { return x + 3 }
+		g := N.Add(3)
 
 		// Modify(f ∘ g)
 		composed := F.Flow2(g, f)

v2/optics/lens/option/from_test.go

@@ -274,7 +274,7 @@ func TestFromIsoModify(t *testing.T) {
 	t.Run("ModifyNoneToSome", func(t *testing.T) {
 		config := Config{timeout: 0, retries: 3}
 		// Map None to Some(10)
-		modified := L.Modify[Config](O.Map(func(x int) int { return x + 10 }))(optTimeoutLens)(config)
+		modified := L.Modify[Config](O.Map(N.Add(10)))(optTimeoutLens)(config)
 		// Since it was None, Map doesn't apply, stays None (0)
 		assert.Equal(t, 0, modified.timeout)
 	})

v2/optics/lens/option/types.go

@@ -31,7 +31,7 @@ type (
 	// by applying a function that takes and returns the same type.
 	//
 	// Example:
-	//   increment := func(x int) int { return x + 1 }
+	//   increment := N.Add(1)
 	//   // increment is an Endomorphism[int]
 	Endomorphism[A any] = endomorphism.Endomorphism[A]
 

v2/optics/optional/optional.go

@@ -18,6 +18,8 @@
 package optional
 
 import (
+	"fmt"
+
 	EM "github.com/IBM/fp-go/v2/endomorphism"
 	F "github.com/IBM/fp-go/v2/function"
 	O "github.com/IBM/fp-go/v2/option"
@@ -27,6 +29,7 @@ import (
 type Optional[S, A any] struct {
 	GetOption func(s S) O.Option[A]
 	Set       func(a A) EM.Endomorphism[S]
+	name      string
 }
 
 // setCopy wraps a setter for a pointer into a setter that first creates a copy before
@@ -41,29 +44,42 @@ func setCopy[SET ~func(*S, A) *S, S, A any](setter SET) func(s *S, a A) *S {
 // MakeOptional creates an Optional based on a getter and a setter function. Make sure that the setter creates a (shallow) copy of the
 // data. This happens automatically if the data is passed by value. For pointers consider to use `MakeOptionalRef`
 // and for other kinds of data structures that are copied by reference make sure the setter creates the copy.
+//
+//go:inline
 func MakeOptional[S, A any](get func(S) O.Option[A], set func(S, A) S) Optional[S, A] {
-	return Optional[S, A]{GetOption: get, Set: F.Bind2of2(set)}
+	return MakeOptionalWithName(get, set, "GenericOptional")
+}
+
+func MakeOptionalWithName[S, A any](get func(S) O.Option[A], set func(S, A) S, name string) Optional[S, A] {
+	return Optional[S, A]{GetOption: get, Set: F.Bind2of2(set), name: name}
 }
 
 // MakeOptionalRef creates an Optional based on a getter and a setter function. The setter passed in does not have to create a shallow
 // copy, the implementation wraps the setter into one that copies the pointer before modifying it
+//
+//go:inline
 func MakeOptionalRef[S, A any](get func(*S) O.Option[A], set func(*S, A) *S) Optional[*S, A] {
 	return MakeOptional(get, setCopy(set))
 }
 
+//go:inline
+func MakeOptionalRefWithName[S, A any](get func(*S) O.Option[A], set func(*S, A) *S, name string) Optional[*S, A] {
+	return MakeOptionalWithName(get, setCopy(set), name)
+}
+
 // Id returns am optional implementing the identity operation
-func id[S any](creator func(get func(S) O.Option[S], set func(S, S) S) Optional[S, S]) Optional[S, S] {
-	return creator(O.Some[S], F.Second[S, S])
+func idWithName[S any](creator func(get func(S) O.Option[S], set func(S, S) S, name string) Optional[S, S], name string) Optional[S, S] {
+	return creator(O.Some[S], F.Second[S, S], name)
 }
 
 // Id returns am optional implementing the identity operation
 func Id[S any]() Optional[S, S] {
-	return id(MakeOptional[S, S])
+	return idWithName(MakeOptionalWithName[S, S], "Identity")
 }
 
 // Id returns am optional implementing the identity operation
 func IdRef[S any]() Optional[*S, *S] {
-	return id(MakeOptionalRef[S, *S])
+	return idWithName(MakeOptionalRefWithName[S, *S], "Identity")
 }
 
 func optionalModifyOption[S, A any](f func(A) A, optional Optional[S, A], s S) O.Option[S] {
@@ -189,3 +205,11 @@ func IChainAny[S, A any]() func(Optional[S, any]) Optional[S, A] {
 		return ichain(sa, fromAny, toAny)
 	}
 }
+
+func (l Optional[S, T]) String() string {
+	return l.name
+}
+
+func (l Optional[S, T]) Format(f fmt.State, c rune) {
+	fmt.Fprint(f, l.String())
+}

v2/optics/optional/prism/prism.go

@@ -33,7 +33,7 @@ func AsOptional[S, A any](sa P.Prism[S, A]) OPT.Optional[S, A] {
 }
 
 func PrismSome[A any]() P.Prism[O.Option[A], A] {
-	return P.MakePrism(F.Identity[O.Option[A]], O.Some[A])
+	return P.MakePrismWithName(F.Identity[O.Option[A]], O.Some[A], "PrismSome")
 }
 
 // Some returns a `Optional` from a `Optional` focused on the `Some` of a `Option` type.

v2/optics/prism/prism.go

@@ -16,6 +16,8 @@
 package prism
 
 import (
+	"fmt"
+
 	EM "github.com/IBM/fp-go/v2/endomorphism"
 	F "github.com/IBM/fp-go/v2/function"
 	O "github.com/IBM/fp-go/v2/option"
@@ -48,33 +50,19 @@ type (
 	//       },
 	//       func(v int) Result { return Success{Value: v} },
 	//   )
-	Prism[S, A any] interface {
+	Prism[S, A any] struct {
 		// GetOption attempts to extract a value of type A from S.
 		// Returns Some(a) if the extraction succeeds, None otherwise.
-		GetOption(s S) Option[A]
+		GetOption O.Kleisli[S, A]
 
 		// ReverseGet constructs an S from an A.
 		// This operation always succeeds.
-		ReverseGet(a A) S
-	}
+		ReverseGet func(A) S
 
-	// prismImpl is the internal implementation of the Prism interface.
-	prismImpl[S, A any] struct {
-		get func(S) Option[A]
-		rev func(A) S
+		name string
 	}
 )
 
-// GetOption implements the Prism interface for prismImpl.
-func (prism prismImpl[S, A]) GetOption(s S) Option[A] {
-	return prism.get(s)
-}
-
-// ReverseGet implements the Prism interface for prismImpl.
-func (prism prismImpl[S, A]) ReverseGet(a A) S {
-	return prism.rev(a)
-}
-
 // MakePrism constructs a Prism from GetOption and ReverseGet functions.
 //
 // Parameters:
@@ -90,8 +78,15 @@ func (prism prismImpl[S, A]) ReverseGet(a A) S {
 //	    func(opt Option[int]) Option[int] { return opt },
 //	    func(n int) Option[int] { return Some(n) },
 //	)
+//
+//go:inline
 func MakePrism[S, A any](get func(S) Option[A], rev func(A) S) Prism[S, A] {
-	return prismImpl[S, A]{get, rev}
+	return MakePrismWithName(get, rev, "GenericPrism")
+}
+
+//go:inline
+func MakePrismWithName[S, A any](get func(S) Option[A], rev func(A) S, name string) Prism[S, A] {
+	return Prism[S, A]{get, rev, name}
 }
 
 // Id returns an identity prism that focuses on the entire value.
@@ -106,7 +101,7 @@ func MakePrism[S, A any](get func(S) Option[A], rev func(A) S) Prism[S, A] {
 //	value := idPrism.GetOption(42)    // Some(42)
 //	result := idPrism.ReverseGet(42)  // 42
 func Id[S any]() Prism[S, S] {
-	return MakePrism(O.Some[S], F.Identity[S])
+	return MakePrismWithName(O.Some[S], F.Identity[S], "PrismIdentity")
 }
 
 // FromPredicate creates a prism that matches values satisfying a predicate.
@@ -125,7 +120,7 @@ func Id[S any]() Prism[S, S] {
 //	value := positivePrism.GetOption(42)  // Some(42)
 //	value = positivePrism.GetOption(-5)   // None[int]
 func FromPredicate[S any](pred func(S) bool) Prism[S, S] {
-	return MakePrism(O.FromPredicate(pred), F.Identity[S])
+	return MakePrismWithName(O.FromPredicate(pred), F.Identity[S], "PrismWithPredicate")
 }
 
 // Compose composes two prisms to create a prism that focuses deeper into a structure.
@@ -149,13 +144,15 @@ func FromPredicate[S any](pred func(S) bool) Prism[S, S] {
 //	composed := Compose[Outer](innerPrism)(outerPrism)  // Prism[Outer, Value]
 func Compose[S, A, B any](ab Prism[A, B]) func(Prism[S, A]) Prism[S, B] {
 	return func(sa Prism[S, A]) Prism[S, B] {
-		return MakePrism(F.Flow2(
+		return MakePrismWithName(F.Flow2(
 			sa.GetOption,
 			O.Chain(ab.GetOption),
 		), F.Flow2(
 			ab.ReverseGet,
 			sa.ReverseGet,
-		))
+		),
+			fmt.Sprintf("PrismCompose[%s x %s]", ab, sa),
+		)
 	}
 }
 
@@ -213,7 +210,7 @@ func Set[S, A any](a A) func(Prism[S, A]) EM.Endomorphism[S] {
 // prismSome creates a prism that focuses on the Some variant of an Option.
 // This is an internal helper used by the Some function.
 func prismSome[A any]() Prism[Option[A], A] {
-	return MakePrism(F.Identity[Option[A]], O.Some[A])
+	return MakePrismWithName(F.Identity[Option[A]], O.Some[A], "PrismSome")
 }
 
 // Some creates a prism that focuses on the Some variant of an Option within a structure.
@@ -242,9 +239,10 @@ func Some[S, A any](soa Prism[S, Option[A]]) Prism[S, A] {
 
 // imap is an internal helper that bidirectionally maps a prism's focus type.
 func imap[S any, AB ~func(A) B, BA ~func(B) A, A, B any](sa Prism[S, A], ab AB, ba BA) Prism[S, B] {
-	return MakePrism(
+	return MakePrismWithName(
 		F.Flow2(sa.GetOption, O.Map(ab)),
 		F.Flow2(ba, sa.ReverseGet),
+		fmt.Sprintf("PrismIMap[%s]", sa),
 	)
 }
 
@@ -278,3 +276,11 @@ func IMap[S any, AB ~func(A) B, BA ~func(B) A, A, B any](ab AB, ba BA) func(Pris
 		return imap(sa, ab, ba)
 	}
 }
+
+func (l Prism[S, T]) String() string {
+	return "Prism"
+}
+
+func (l Prism[S, T]) Format(f fmt.State, c rune) {
+	fmt.Fprint(f, l.String())
+}

v2/optics/prism/prisms.go

@@ -17,8 +17,10 @@ package prism
 
 import (
 	"encoding/base64"
+	"fmt"
 	"net/url"
 	"regexp"
+	"strconv"
 	"time"
 
 	"github.com/IBM/fp-go/v2/either"
@@ -67,10 +69,12 @@ import (
 //   - Validating and transforming base64 data in pipelines
 //   - Using different encodings (Standard, URL-safe, RawStd, RawURL)
 func FromEncoding(enc *base64.Encoding) Prism[string, []byte] {
-	return MakePrism(F.Flow2(
+	return MakePrismWithName(F.Flow2(
 		either.Eitherize1(enc.DecodeString),
 		either.Fold(F.Ignore1of1[error](option.None[[]byte]), option.Some),
-	), enc.EncodeToString)
+	), enc.EncodeToString,
+		"PrismFromEncoding",
+	)
 }
 
 // ParseURL creates a prism for parsing and formatting URLs.
@@ -114,10 +118,12 @@ func FromEncoding(enc *base64.Encoding) Prism[string, []byte] {
 //   - Transforming URL strings in data pipelines
 //   - Extracting and modifying URL components safely
 func ParseURL() Prism[string, *url.URL] {
-	return MakePrism(F.Flow2(
+	return MakePrismWithName(F.Flow2(
 		either.Eitherize1(url.Parse),
 		either.Fold(F.Ignore1of1[error](option.None[*url.URL]), option.Some),
-	), (*url.URL).String)
+	), (*url.URL).String,
+		"PrismParseURL",
+	)
 }
 
 // InstanceOf creates a prism for type assertions on interface{}/any values.
@@ -161,7 +167,8 @@ func ParseURL() Prism[string, *url.URL] {
 //   - Type-safe deserialization and validation
 //   - Pattern matching on interface{} values
 func InstanceOf[T any]() Prism[any, T] {
-	return MakePrism(option.ToType[T], F.ToAny[T])
+	var t T
+	return MakePrismWithName(option.ToType[T], F.ToAny[T], fmt.Sprintf("PrismInstanceOf[%T]", t))
 }
 
 // ParseDate creates a prism for parsing and formatting dates with a specific layout.
@@ -212,10 +219,12 @@ func InstanceOf[T any]() Prism[any, T] {
 //   - Converting between date formats
 //   - Safely handling user-provided date inputs
 func ParseDate(layout string) Prism[string, time.Time] {
-	return MakePrism(F.Flow2(
+	return MakePrismWithName(F.Flow2(
 		F.Bind1st(either.Eitherize2(time.Parse), layout),
 		either.Fold(F.Ignore1of1[error](option.None[time.Time]), option.Some),
-	), F.Bind2nd(time.Time.Format, layout))
+	), F.Bind2nd(time.Time.Format, layout),
+		"PrismParseDate",
+	)
 }
 
 // Deref creates a prism for safely dereferencing pointers.
@@ -263,7 +272,7 @@ func ParseDate(layout string) Prism[string, time.Time] {
 //   - Filtering out nil values in data pipelines
 //   - Working with database nullable columns
 func Deref[T any]() Prism[*T, *T] {
-	return MakePrism(option.FromNillable[T], F.Identity[*T])
+	return MakePrismWithName(option.FromNillable[T], F.Identity[*T], "PrismDeref")
 }
 
 // FromEither creates a prism for extracting Right values from Either types.
@@ -309,7 +318,7 @@ func Deref[T any]() Prism[*T, *T] {
 //   - Working with fallible operations
 //   - Composing with other prisms for complex error handling
 func FromEither[E, T any]() Prism[Either[E, T], T] {
-	return MakePrism(either.ToOption[E, T], either.Of[E, T])
+	return MakePrismWithName(either.ToOption[E, T], either.Of[E, T], "PrismFromEither")
 }
 
 // FromZero creates a prism that matches zero values of comparable types.
@@ -352,11 +361,50 @@ func FromEither[E, T any]() Prism[Either[E, T], T] {
 //   - Working with optional fields that use zero as "not set"
 //   - Replacing zero values with defaults
 func FromZero[T comparable]() Prism[T, T] {
-	return MakePrism(option.FromZero[T](), F.Identity[T])
+	return MakePrismWithName(option.FromZero[T](), F.Identity[T], "PrismFromZero")
 }
 
+// FromNonZero creates a prism that matches non-zero values of comparable types.
+// It provides a safe way to work with non-zero values, handling zero values
+// gracefully through the Option type.
+//
+// The prism's GetOption returns Some(t) if the value is not equal to the zero value
+// of type T; otherwise, it returns None.
+//
+// The prism's ReverseGet is the identity function, returning the value unchanged.
+//
+// Type Parameters:
+//   - T: A comparable type (must support == and != operators)
+//
+// Returns:
+//   - A Prism[T, T] that matches non-zero values
+//
+// Example:
+//
+//	// Create a prism for non-zero integers
+//	nonZeroPrism := FromNonZero[int]()
+//
+//	// Match non-zero value
+//	result := nonZeroPrism.GetOption(42)  // Some(42)
+//
+//	// Zero returns None
+//	result = nonZeroPrism.GetOption(0)  // None[int]()
+//
+//	// ReverseGet is identity
+//	value := nonZeroPrism.ReverseGet(42)  // 42
+//
+//	// Use with Set to update non-zero values
+//	setter := Set[int, int](100)
+//	result := setter(nonZeroPrism)(42)   // 100
+//	result = setter(nonZeroPrism)(0)     // 0 (unchanged)
+//
+// Common use cases:
+//   - Validating that values are non-zero/non-default
+//   - Filtering non-zero values in data pipelines
+//   - Working with required fields that shouldn't be zero
+//   - Replacing non-zero values with new values
 func FromNonZero[T comparable]() Prism[T, T] {
-	return MakePrism(option.FromNonZero[T](), F.Identity[T])
+	return MakePrismWithName(option.FromNonZero[T](), F.Identity[T], "PrismFromNonZero")
 }
 
 // Match represents a regex match result with full reconstruction capability.
@@ -495,7 +543,7 @@ func (m Match) Group(n int) string {
 func RegexMatcher(re *regexp.Regexp) Prism[string, Match] {
 	noMatch := option.None[Match]()
 
-	return MakePrism(
+	return MakePrismWithName(
 		// String -> Option[Match]
 		func(s string) Option[Match] {
 			loc := re.FindStringSubmatchIndex(s)
@@ -522,6 +570,7 @@ func RegexMatcher(re *regexp.Regexp) Prism[string, Match] {
 			return option.Some(match)
 		},
 		Match.Reconstruct,
+		fmt.Sprintf("PrismRegex[%s]", re),
 	)
 }
 
@@ -660,3 +709,259 @@ func RegexNamedMatcher(re *regexp.Regexp) Prism[string, NamedMatch] {
 		NamedMatch.Reconstruct,
 	)
 }
+
+func getFromEither[A, B any](f func(A) (B, error)) func(A) Option[B] {
+	return func(a A) Option[B] {
+		b, err := f(a)
+		if err != nil {
+			return option.None[B]()
+		}
+		return option.Of(b)
+	}
+}
+
+func atoi64(s string) (int64, error) {
+	return strconv.ParseInt(s, 10, 64)
+}
+
+func itoa64(i int64) string {
+	return strconv.FormatInt(i, 10)
+}
+
+// ParseInt creates a prism for parsing and formatting integers.
+// It provides a safe way to convert between string and int, handling
+// parsing errors gracefully through the Option type.
+//
+// The prism's GetOption attempts to parse a string into an int.
+// If parsing succeeds, it returns Some(int); if it fails (e.g., invalid
+// number format), it returns None.
+//
+// The prism's ReverseGet always succeeds, converting an int to its string representation.
+//
+// Returns:
+//   - A Prism[string, int] that safely handles int parsing/formatting
+//
+// Example:
+//
+//	// Create an int parsing prism
+//	intPrism := ParseInt()
+//
+//	// Parse valid integer
+//	parsed := intPrism.GetOption("42")  // Some(42)
+//
+//	// Parse invalid integer
+//	invalid := intPrism.GetOption("not-a-number")  // None[int]()
+//
+//	// Format int to string
+//	str := intPrism.ReverseGet(42)  // "42"
+//
+//	// Use with Set to update integer values
+//	setter := Set[string, int](100)
+//	result := setter(intPrism)("42")  // "100"
+//
+// Common use cases:
+//   - Parsing integer configuration values
+//   - Validating numeric user input
+//   - Converting between string and int in data pipelines
+//   - Working with numeric API parameters
+//
+//go:inline
+func ParseInt() Prism[string, int] {
+	return MakePrismWithName(getFromEither(strconv.Atoi), strconv.Itoa, "PrismParseInt")
+}
+
+// ParseInt64 creates a prism for parsing and formatting 64-bit integers.
+// It provides a safe way to convert between string and int64, handling
+// parsing errors gracefully through the Option type.
+//
+// The prism's GetOption attempts to parse a string into an int64.
+// If parsing succeeds, it returns Some(int64); if it fails (e.g., invalid
+// number format or overflow), it returns None.
+//
+// The prism's ReverseGet always succeeds, converting an int64 to its string representation.
+//
+// Returns:
+//   - A Prism[string, int64] that safely handles int64 parsing/formatting
+//
+// Example:
+//
+//	// Create an int64 parsing prism
+//	int64Prism := ParseInt64()
+//
+//	// Parse valid 64-bit integer
+//	parsed := int64Prism.GetOption("9223372036854775807")  // Some(9223372036854775807)
+//
+//	// Parse invalid integer
+//	invalid := int64Prism.GetOption("not-a-number")  // None[int64]()
+//
+//	// Format int64 to string
+//	str := int64Prism.ReverseGet(int64(42))  // "42"
+//
+//	// Use with Set to update int64 values
+//	setter := Set[string, int64](int64(100))
+//	result := setter(int64Prism)("42")  // "100"
+//
+// Common use cases:
+//   - Parsing large integer values (timestamps, IDs)
+//   - Working with database integer columns
+//   - Handling 64-bit numeric API parameters
+//   - Converting between string and int64 in data pipelines
+//
+//go:inline
+func ParseInt64() Prism[string, int64] {
+	return MakePrismWithName(getFromEither(atoi64), itoa64, "PrismParseInt64")
+}
+
+// ParseBool creates a prism for parsing and formatting boolean values.
+// It provides a safe way to convert between string and bool, handling
+// parsing errors gracefully through the Option type.
+//
+// The prism's GetOption attempts to parse a string into a bool.
+// It accepts "1", "t", "T", "TRUE", "true", "True", "0", "f", "F", "FALSE", "false", "False".
+// If parsing succeeds, it returns Some(bool); if it fails, it returns None.
+//
+// The prism's ReverseGet always succeeds, converting a bool to "true" or "false".
+//
+// Returns:
+//   - A Prism[string, bool] that safely handles bool parsing/formatting
+//
+// Example:
+//
+//	// Create a bool parsing prism
+//	boolPrism := ParseBool()
+//
+//	// Parse valid boolean strings
+//	parsed := boolPrism.GetOption("true")   // Some(true)
+//	parsed = boolPrism.GetOption("1")       // Some(true)
+//	parsed = boolPrism.GetOption("false")   // Some(false)
+//	parsed = boolPrism.GetOption("0")       // Some(false)
+//
+//	// Parse invalid boolean
+//	invalid := boolPrism.GetOption("maybe")  // None[bool]()
+//
+//	// Format bool to string
+//	str := boolPrism.ReverseGet(true)   // "true"
+//	str = boolPrism.ReverseGet(false)   // "false"
+//
+//	// Use with Set to update boolean values
+//	setter := Set[string, bool](true)
+//	result := setter(boolPrism)("false")  // "true"
+//
+// Common use cases:
+//   - Parsing boolean configuration values
+//   - Validating boolean user input
+//   - Converting between string and bool in data pipelines
+//   - Working with boolean API parameters or flags
+//
+//go:inline
+func ParseBool() Prism[string, bool] {
+	return MakePrismWithName(getFromEither(strconv.ParseBool), strconv.FormatBool, "PrismParseBool")
+}
+
+func atof64(s string) (float64, error) {
+	return strconv.ParseFloat(s, 64)
+}
+
+func atof32(s string) (float32, error) {
+	f32, err := strconv.ParseFloat(s, 32)
+	if err != nil {
+		return 0, err
+	}
+	return float32(f32), nil
+}
+
+func f32toa(f float32) string {
+	return strconv.FormatFloat(float64(f), 'g', -1, 32)
+}
+
+func f64toa(f float64) string {
+	return strconv.FormatFloat(f, 'g', -1, 64)
+}
+
+// ParseFloat32 creates a prism for parsing and formatting 32-bit floating-point numbers.
+// It provides a safe way to convert between string and float32, handling
+// parsing errors gracefully through the Option type.
+//
+// The prism's GetOption attempts to parse a string into a float32.
+// If parsing succeeds, it returns Some(float32); if it fails (e.g., invalid
+// number format or overflow), it returns None.
+//
+// The prism's ReverseGet always succeeds, converting a float32 to its string representation
+// using the 'g' format (shortest representation).
+//
+// Returns:
+//   - A Prism[string, float32] that safely handles float32 parsing/formatting
+//
+// Example:
+//
+//	// Create a float32 parsing prism
+//	float32Prism := ParseFloat32()
+//
+//	// Parse valid float
+//	parsed := float32Prism.GetOption("3.14")  // Some(3.14)
+//	parsed = float32Prism.GetOption("1.5e10") // Some(1.5e10)
+//
+//	// Parse invalid float
+//	invalid := float32Prism.GetOption("not-a-number")  // None[float32]()
+//
+//	// Format float32 to string
+//	str := float32Prism.ReverseGet(float32(3.14))  // "3.14"
+//
+//	// Use with Set to update float32 values
+//	setter := Set[string, float32](float32(2.71))
+//	result := setter(float32Prism)("3.14")  // "2.71"
+//
+// Common use cases:
+//   - Parsing floating-point configuration values
+//   - Working with scientific notation
+//   - Converting between string and float32 in data pipelines
+//   - Handling numeric API parameters with decimal precision
+//
+//go:inline
+func ParseFloat32() Prism[string, float32] {
+	return MakePrismWithName(getFromEither(atof32), f32toa, "ParseFloat32")
+}
+
+// ParseFloat64 creates a prism for parsing and formatting 64-bit floating-point numbers.
+// It provides a safe way to convert between string and float64, handling
+// parsing errors gracefully through the Option type.
+//
+// The prism's GetOption attempts to parse a string into a float64.
+// If parsing succeeds, it returns Some(float64); if it fails (e.g., invalid
+// number format or overflow), it returns None.
+//
+// The prism's ReverseGet always succeeds, converting a float64 to its string representation
+// using the 'g' format (shortest representation).
+//
+// Returns:
+//   - A Prism[string, float64] that safely handles float64 parsing/formatting
+//
+// Example:
+//
+//	// Create a float64 parsing prism
+//	float64Prism := ParseFloat64()
+//
+//	// Parse valid float
+//	parsed := float64Prism.GetOption("3.141592653589793")  // Some(3.141592653589793)
+//	parsed = float64Prism.GetOption("1.5e100")             // Some(1.5e100)
+//
+//	// Parse invalid float
+//	invalid := float64Prism.GetOption("not-a-number")  // None[float64]()
+//
+//	// Format float64 to string
+//	str := float64Prism.ReverseGet(3.141592653589793)  // "3.141592653589793"
+//
+//	// Use with Set to update float64 values
+//	setter := Set[string, float64](2.718281828459045)
+//	result := setter(float64Prism)("3.14")  // "2.718281828459045"
+//
+// Common use cases:
+//   - Parsing high-precision floating-point values
+//   - Working with scientific notation and large numbers
+//   - Converting between string and float64 in data pipelines
+//   - Handling precise numeric API parameters
+//
+//go:inline
+func ParseFloat64() Prism[string, float64] {
+	return MakePrismWithName(getFromEither(atof64), f64toa, "PrismParseFloat64")
+}

v2/optics/prism/prisms_test.go

@@ -532,3 +532,411 @@ func TestRegexNamedMatcherWithSet(t *testing.T) {
 		assert.Equal(t, original, result)
 	})
 }
+
+// TestFromNonZero tests the FromNonZero prism with various comparable types
+func TestFromNonZero(t *testing.T) {
+	t.Run("int - match non-zero", func(t *testing.T) {
+		prism := FromNonZero[int]()
+
+		result := prism.GetOption(42)
+		assert.True(t, O.IsSome(result))
+		assert.Equal(t, 42, O.GetOrElse(F.Constant(-1))(result))
+	})
+
+	t.Run("int - zero returns None", func(t *testing.T) {
+		prism := FromNonZero[int]()
+
+		result := prism.GetOption(0)
+		assert.True(t, O.IsNone(result))
+	})
+
+	t.Run("string - match non-empty string", func(t *testing.T) {
+		prism := FromNonZero[string]()
+
+		result := prism.GetOption("hello")
+		assert.True(t, O.IsSome(result))
+		assert.Equal(t, "hello", O.GetOrElse(F.Constant("default"))(result))
+	})
+
+	t.Run("string - empty returns None", func(t *testing.T) {
+		prism := FromNonZero[string]()
+
+		result := prism.GetOption("")
+		assert.True(t, O.IsNone(result))
+	})
+
+	t.Run("bool - match true", func(t *testing.T) {
+		prism := FromNonZero[bool]()
+
+		result := prism.GetOption(true)
+		assert.True(t, O.IsSome(result))
+		assert.True(t, O.GetOrElse(F.Constant(false))(result))
+	})
+
+	t.Run("bool - false returns None", func(t *testing.T) {
+		prism := FromNonZero[bool]()
+
+		result := prism.GetOption(false)
+		assert.True(t, O.IsNone(result))
+	})
+
+	t.Run("float64 - match non-zero", func(t *testing.T) {
+		prism := FromNonZero[float64]()
+
+		result := prism.GetOption(3.14)
+		assert.True(t, O.IsSome(result))
+		assert.Equal(t, 3.14, O.GetOrElse(F.Constant(-1.0))(result))
+	})
+
+	t.Run("float64 - zero returns None", func(t *testing.T) {
+		prism := FromNonZero[float64]()
+
+		result := prism.GetOption(0.0)
+		assert.True(t, O.IsNone(result))
+	})
+
+	t.Run("pointer - match non-nil", func(t *testing.T) {
+		prism := FromNonZero[*int]()
+
+		value := 42
+		result := prism.GetOption(&value)
+		assert.True(t, O.IsSome(result))
+	})
+
+	t.Run("pointer - nil returns None", func(t *testing.T) {
+		prism := FromNonZero[*int]()
+
+		var nilPtr *int
+		result := prism.GetOption(nilPtr)
+		assert.True(t, O.IsNone(result))
+	})
+
+	t.Run("reverse get is identity", func(t *testing.T) {
+		prism := FromNonZero[int]()
+
+		assert.Equal(t, 0, prism.ReverseGet(0))
+		assert.Equal(t, 42, prism.ReverseGet(42))
+	})
+}
+
+// TestFromNonZeroWithSet tests using Set with FromNonZero prism
+func TestFromNonZeroWithSet(t *testing.T) {
+	t.Run("set on non-zero value", func(t *testing.T) {
+		prism := FromNonZero[int]()
+
+		setter := Set[int](100)
+		result := setter(prism)(42)
+
+		assert.Equal(t, 100, result)
+	})
+
+	t.Run("set on zero returns original", func(t *testing.T) {
+		prism := FromNonZero[int]()
+
+		setter := Set[int](100)
+		result := setter(prism)(0)
+
+		assert.Equal(t, 0, result)
+	})
+}
+
+// TestParseInt tests the ParseInt prism
+func TestParseInt(t *testing.T) {
+	prism := ParseInt()
+
+	t.Run("parse valid positive integer", func(t *testing.T) {
+		result := prism.GetOption("42")
+		assert.True(t, O.IsSome(result))
+		assert.Equal(t, 42, O.GetOrElse(F.Constant(-1))(result))
+	})
+
+	t.Run("parse valid negative integer", func(t *testing.T) {
+		result := prism.GetOption("-123")
+		assert.True(t, O.IsSome(result))
+		assert.Equal(t, -123, O.GetOrElse(F.Constant(0))(result))
+	})
+
+	t.Run("parse zero", func(t *testing.T) {
+		result := prism.GetOption("0")
+		assert.True(t, O.IsSome(result))
+		assert.Equal(t, 0, O.GetOrElse(F.Constant(-1))(result))
+	})
+
+	t.Run("parse invalid integer", func(t *testing.T) {
+		result := prism.GetOption("not-a-number")
+		assert.True(t, O.IsNone(result))
+	})
+
+	t.Run("parse float as integer fails", func(t *testing.T) {
+		result := prism.GetOption("3.14")
+		assert.True(t, O.IsNone(result))
+	})
+
+	t.Run("parse empty string fails", func(t *testing.T) {
+		result := prism.GetOption("")
+		assert.True(t, O.IsNone(result))
+	})
+
+	t.Run("reverse get formats integer", func(t *testing.T) {
+		assert.Equal(t, "42", prism.ReverseGet(42))
+		assert.Equal(t, "-123", prism.ReverseGet(-123))
+		assert.Equal(t, "0", prism.ReverseGet(0))
+	})
+
+	t.Run("round trip", func(t *testing.T) {
+		original := "12345"
+		result := prism.GetOption(original)
+		if O.IsSome(result) {
+			value := O.GetOrElse(F.Constant(0))(result)
+			reconstructed := prism.ReverseGet(value)
+			assert.Equal(t, original, reconstructed)
+		}
+	})
+}
+
+// TestParseInt64 tests the ParseInt64 prism
+func TestParseInt64(t *testing.T) {
+	prism := ParseInt64()
+
+	t.Run("parse valid int64", func(t *testing.T) {
+		result := prism.GetOption("9223372036854775807")
+		assert.True(t, O.IsSome(result))
+		assert.Equal(t, int64(9223372036854775807), O.GetOrElse(F.Constant(int64(-1)))(result))
+	})
+
+	t.Run("parse negative int64", func(t *testing.T) {
+		result := prism.GetOption("-9223372036854775808")
+		assert.True(t, O.IsSome(result))
+		assert.Equal(t, int64(-9223372036854775808), O.GetOrElse(F.Constant(int64(0)))(result))
+	})
+
+	t.Run("parse invalid int64", func(t *testing.T) {
+		result := prism.GetOption("not-a-number")
+		assert.True(t, O.IsNone(result))
+	})
+
+	t.Run("reverse get formats int64", func(t *testing.T) {
+		assert.Equal(t, "42", prism.ReverseGet(int64(42)))
+		assert.Equal(t, "9223372036854775807", prism.ReverseGet(int64(9223372036854775807)))
+	})
+
+	t.Run("round trip", func(t *testing.T) {
+		original := "1234567890123456789"
+		result := prism.GetOption(original)
+		if O.IsSome(result) {
+			value := O.GetOrElse(F.Constant(int64(0)))(result)
+			reconstructed := prism.ReverseGet(value)
+			assert.Equal(t, original, reconstructed)
+		}
+	})
+}
+
+// TestParseBool tests the ParseBool prism
+func TestParseBool(t *testing.T) {
+	prism := ParseBool()
+
+	t.Run("parse true variations", func(t *testing.T) {
+		trueValues := []string{"true", "True", "TRUE", "t", "T", "1"}
+		for _, val := range trueValues {
+			result := prism.GetOption(val)
+			assert.True(t, O.IsSome(result), "Should parse: %s", val)
+			assert.True(t, O.GetOrElse(F.Constant(false))(result), "Should be true: %s", val)
+		}
+	})
+
+	t.Run("parse false variations", func(t *testing.T) {
+		falseValues := []string{"false", "False", "FALSE", "f", "F", "0"}
+		for _, val := range falseValues {
+			result := prism.GetOption(val)
+			assert.True(t, O.IsSome(result), "Should parse: %s", val)
+			assert.False(t, O.GetOrElse(F.Constant(true))(result), "Should be false: %s", val)
+		}
+	})
+
+	t.Run("parse invalid bool", func(t *testing.T) {
+		invalidValues := []string{"maybe", "yes", "no", "2", ""}
+		for _, val := range invalidValues {
+			result := prism.GetOption(val)
+			assert.True(t, O.IsNone(result), "Should not parse: %s", val)
+		}
+	})
+
+	t.Run("reverse get formats bool", func(t *testing.T) {
+		assert.Equal(t, "true", prism.ReverseGet(true))
+		assert.Equal(t, "false", prism.ReverseGet(false))
+	})
+
+	t.Run("round trip with true", func(t *testing.T) {
+		result := prism.GetOption("true")
+		if O.IsSome(result) {
+			value := O.GetOrElse(F.Constant(false))(result)
+			reconstructed := prism.ReverseGet(value)
+			assert.Equal(t, "true", reconstructed)
+		}
+	})
+
+	t.Run("round trip with false", func(t *testing.T) {
+		result := prism.GetOption("false")
+		if O.IsSome(result) {
+			value := O.GetOrElse(F.Constant(true))(result)
+			reconstructed := prism.ReverseGet(value)
+			assert.Equal(t, "false", reconstructed)
+		}
+	})
+}
+
+// TestParseFloat32 tests the ParseFloat32 prism
+func TestParseFloat32(t *testing.T) {
+	prism := ParseFloat32()
+
+	t.Run("parse valid float32", func(t *testing.T) {
+		result := prism.GetOption("3.14")
+		assert.True(t, O.IsSome(result))
+		value := O.GetOrElse(F.Constant(float32(0)))(result)
+		assert.InDelta(t, float32(3.14), value, 0.0001)
+	})
+
+	t.Run("parse negative float32", func(t *testing.T) {
+		result := prism.GetOption("-2.71")
+		assert.True(t, O.IsSome(result))
+		value := O.GetOrElse(F.Constant(float32(0)))(result)
+		assert.InDelta(t, float32(-2.71), value, 0.0001)
+	})
+
+	t.Run("parse scientific notation", func(t *testing.T) {
+		result := prism.GetOption("1.5e10")
+		assert.True(t, O.IsSome(result))
+		value := O.GetOrElse(F.Constant(float32(0)))(result)
+		assert.InDelta(t, float32(1.5e10), value, 1e6)
+	})
+
+	t.Run("parse integer as float", func(t *testing.T) {
+		result := prism.GetOption("42")
+		assert.True(t, O.IsSome(result))
+		value := O.GetOrElse(F.Constant(float32(0)))(result)
+		assert.Equal(t, float32(42), value)
+	})
+
+	t.Run("parse invalid float", func(t *testing.T) {
+		result := prism.GetOption("not-a-number")
+		assert.True(t, O.IsNone(result))
+	})
+
+	t.Run("reverse get formats float32", func(t *testing.T) {
+		str := prism.ReverseGet(float32(3.14))
+		assert.Contains(t, str, "3.14")
+	})
+
+	t.Run("round trip", func(t *testing.T) {
+		original := "3.14159"
+		result := prism.GetOption(original)
+		if O.IsSome(result) {
+			value := O.GetOrElse(F.Constant(float32(0)))(result)
+			reconstructed := prism.ReverseGet(value)
+			// Parse both to compare as floats due to precision
+			origFloat := F.Pipe1(original, prism.GetOption)
+			reconFloat := F.Pipe1(reconstructed, prism.GetOption)
+			if O.IsSome(origFloat) && O.IsSome(reconFloat) {
+				assert.InDelta(t,
+					O.GetOrElse(F.Constant(float32(0)))(origFloat),
+					O.GetOrElse(F.Constant(float32(0)))(reconFloat),
+					0.0001)
+			}
+		}
+	})
+}
+
+// TestParseFloat64 tests the ParseFloat64 prism
+func TestParseFloat64(t *testing.T) {
+	prism := ParseFloat64()
+
+	t.Run("parse valid float64", func(t *testing.T) {
+		result := prism.GetOption("3.141592653589793")
+		assert.True(t, O.IsSome(result))
+		value := O.GetOrElse(F.Constant(0.0))(result)
+		assert.InDelta(t, 3.141592653589793, value, 1e-15)
+	})
+
+	t.Run("parse negative float64", func(t *testing.T) {
+		result := prism.GetOption("-2.718281828459045")
+		assert.True(t, O.IsSome(result))
+		value := O.GetOrElse(F.Constant(0.0))(result)
+		assert.InDelta(t, -2.718281828459045, value, 1e-15)
+	})
+
+	t.Run("parse scientific notation", func(t *testing.T) {
+		result := prism.GetOption("1.5e100")
+		assert.True(t, O.IsSome(result))
+		value := O.GetOrElse(F.Constant(0.0))(result)
+		assert.InDelta(t, 1.5e100, value, 1e85)
+	})
+
+	t.Run("parse integer as float", func(t *testing.T) {
+		result := prism.GetOption("42")
+		assert.True(t, O.IsSome(result))
+		value := O.GetOrElse(F.Constant(0.0))(result)
+		assert.Equal(t, 42.0, value)
+	})
+
+	t.Run("parse invalid float", func(t *testing.T) {
+		result := prism.GetOption("not-a-number")
+		assert.True(t, O.IsNone(result))
+	})
+
+	t.Run("reverse get formats float64", func(t *testing.T) {
+		str := prism.ReverseGet(3.141592653589793)
+		assert.Contains(t, str, "3.14159")
+	})
+
+	t.Run("round trip", func(t *testing.T) {
+		original := "3.141592653589793"
+		result := prism.GetOption(original)
+		if O.IsSome(result) {
+			value := O.GetOrElse(F.Constant(0.0))(result)
+			reconstructed := prism.ReverseGet(value)
+			// Parse both to compare as floats
+			origFloat := F.Pipe1(original, prism.GetOption)
+			reconFloat := F.Pipe1(reconstructed, prism.GetOption)
+			if O.IsSome(origFloat) && O.IsSome(reconFloat) {
+				assert.InDelta(t,
+					O.GetOrElse(F.Constant(0.0))(origFloat),
+					O.GetOrElse(F.Constant(0.0))(reconFloat),
+					1e-15)
+			}
+		}
+	})
+}
+
+// TestParseIntWithSet tests using Set with ParseInt prism
+func TestParseIntWithSet(t *testing.T) {
+	prism := ParseInt()
+
+	t.Run("set on valid integer string", func(t *testing.T) {
+		setter := Set[string](100)
+		result := setter(prism)("42")
+		assert.Equal(t, "100", result)
+	})
+
+	t.Run("set on invalid string returns original", func(t *testing.T) {
+		setter := Set[string](100)
+		result := setter(prism)("not-a-number")
+		assert.Equal(t, "not-a-number", result)
+	})
+}
+
+// TestParseBoolWithSet tests using Set with ParseBool prism
+func TestParseBoolWithSet(t *testing.T) {
+	prism := ParseBool()
+
+	t.Run("set on valid bool string", func(t *testing.T) {
+		setter := Set[string](true)
+		result := setter(prism)("false")
+		assert.Equal(t, "true", result)
+	})
+
+	t.Run("set on invalid string returns original", func(t *testing.T) {
+		setter := Set[string](true)
+		result := setter(prism)("maybe")
+		assert.Equal(t, "maybe", result)
+	})
+}

v2/option/benchmark_test.go

@@ -17,6 +17,8 @@ package option
 
 import (
 	"testing"
+
+	N "github.com/IBM/fp-go/v2/number"
 )
 
 // Benchmark basic construction
@@ -46,7 +48,7 @@ func BenchmarkIsSome(b *testing.B) {
 
 func BenchmarkMap(b *testing.B) {
 	opt := Some(21)
-	mapper := Map(func(x int) int { return x * 2 })
+	mapper := Map(N.Mul(2))
 	b.ReportAllocs()
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {

v2/option/chain_benchmark_test.go

@@ -17,6 +17,8 @@ package option
 
 import (
 	"testing"
+
+	N "github.com/IBM/fp-go/v2/number"
 )
 
 // Benchmark shallow chain (1 step)
@@ -121,11 +123,11 @@ func BenchmarkMap_5Steps(b *testing.B) {
 	b.ReportAllocs()
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
-		_ = Map(func(x int) int { return x - 10 })(
-			Map(func(x int) int { return x / 2 })(
-				Map(func(x int) int { return x + 20 })(
-					Map(func(x int) int { return x * 3 })(
-						Map(func(x int) int { return x + 1 })(opt),
+		_ = Map(N.Sub(10))(
+			Map(N.Div(2))(
+				Map(N.Add(20))(
+					Map(N.Mul(3))(
+						Map(N.Add(1))(opt),
 					),
 				),
 			),

v2/reader/reader.go

@@ -289,11 +289,11 @@ func Read[A, E any](e E) func(Reader[E, A]) A {
 //
 //	type Config struct { Multiplier int }
 //	getMultiplier := func(c Config) func(int) int {
-//	    return func(x int) int { return x * c.Multiplier }
+//	    return N.Mul(c.Multiplier)
 //	}
 //	r := reader.MonadFlap(getMultiplier, 5)
 //	result := r(Config{Multiplier: 3}) // 15
-func MonadFlap[R, A, B any](fab Reader[R, func(A) B], a A) Reader[R, B] {
+func MonadFlap[R, B, A any](fab Reader[R, func(A) B], a A) Reader[R, B] {
 	return functor.MonadFlap(MonadMap[R, func(A) B, B], fab, a)
 }
 
@@ -304,11 +304,11 @@ func MonadFlap[R, A, B any](fab Reader[R, func(A) B], a A) Reader[R, B] {
 //
 //	type Config struct { Multiplier int }
 //	getMultiplier := reader.Asks(func(c Config) func(int) int {
-//	    return func(x int) int { return x * c.Multiplier }
+//	    return N.Mul(c.Multiplier)
 //	})
 //	applyTo5 := reader.Flap[Config](5)
 //	r := applyTo5(getMultiplier)
 //	result := r(Config{Multiplier: 3}) // 15
-func Flap[R, A, B any](a A) Operator[R, func(A) B, B] {
+func Flap[R, B, A any](a A) Operator[R, func(A) B, B] {
 	return functor.Flap(Map[R, func(A) B, B], a)
 }

v2/reader/reader_test.go

@@ -184,7 +184,7 @@ func TestRead(t *testing.T) {
 func TestMonadFlap(t *testing.T) {
 	config := Config{Multiplier: 3}
 	getMultiplier := func(c Config) func(int) int {
-		return func(x int) int { return x * c.Multiplier }
+		return N.Mul(c.Multiplier)
 	}
 	r := MonadFlap(getMultiplier, 5)
 	result := r(config)
@@ -194,9 +194,9 @@ func TestMonadFlap(t *testing.T) {
 func TestFlap(t *testing.T) {
 	config := Config{Multiplier: 3}
 	getMultiplier := Asks(func(c Config) func(int) int {
-		return func(x int) int { return x * c.Multiplier }
+		return N.Mul(c.Multiplier)
 	})
-	applyTo5 := Flap[Config, int, int](5)
+	applyTo5 := Flap[Config, int](5)
 	r := applyTo5(getMultiplier)
 	result := r(config)
 	assert.Equal(t, 15, result)

v2/readerioeither/array.go

@@ -0,0 +1,83 @@
+package readerioeither
+
+import (
+	"github.com/IBM/fp-go/v2/function"
+	RA "github.com/IBM/fp-go/v2/internal/array"
+	"github.com/IBM/fp-go/v2/monoid"
+)
+
+//go:inline
+func MonadReduceArray[R, E, A, B any](as []ReaderIOEither[R, E, A], reduce func(B, A) B, initial B) ReaderIOEither[R, E, B] {
+	return RA.MonadTraverseReduce(
+		Of,
+		Map,
+		Ap,
+
+		as,
+
+		function.Identity[ReaderIOEither[R, E, A]],
+		reduce,
+		initial,
+	)
+}
+
+//go:inline
+func ReduceArray[R, E, A, B any](reduce func(B, A) B, initial B) Kleisli[R, E, []ReaderIOEither[R, E, A], B] {
+	return RA.TraverseReduce[[]ReaderIOEither[R, E, A]](
+		Of,
+		Map,
+		Ap,
+
+		function.Identity[ReaderIOEither[R, E, A]],
+		reduce,
+		initial,
+	)
+}
+
+//go:inline
+func MonadReduceArrayM[R, E, A any](as []ReaderIOEither[R, E, A], m monoid.Monoid[A]) ReaderIOEither[R, E, A] {
+	return MonadReduceArray(as, m.Concat, m.Empty())
+}
+
+//go:inline
+func ReduceArrayM[R, E, A any](m monoid.Monoid[A]) Kleisli[R, E, []ReaderIOEither[R, E, A], A] {
+	return ReduceArray[R, E](m.Concat, m.Empty())
+}
+
+//go:inline
+func MonadTraverseReduceArray[R, E, A, B, C any](as []A, trfrm Kleisli[R, E, A, B], reduce func(C, B) C, initial C) ReaderIOEither[R, E, C] {
+	return RA.MonadTraverseReduce(
+		Of,
+		Map,
+		Ap,
+
+		as,
+
+		trfrm,
+		reduce,
+		initial,
+	)
+}
+
+//go:inline
+func TraverseReduceArray[R, E, A, B, C any](trfrm Kleisli[R, E, A, B], reduce func(C, B) C, initial C) Kleisli[R, E, []A, C] {
+	return RA.TraverseReduce[[]A](
+		Of,
+		Map,
+		Ap,
+
+		trfrm,
+		reduce,
+		initial,
+	)
+}
+
+//go:inline
+func MonadTraverseReduceArrayM[R, E, A, B any](as []A, trfrm Kleisli[R, E, A, B], m monoid.Monoid[B]) ReaderIOEither[R, E, B] {
+	return MonadTraverseReduceArray(as, trfrm, m.Concat, m.Empty())
+}
+
+//go:inline
+func TraverseReduceArrayM[R, E, A, B any](trfrm Kleisli[R, E, A, B], m monoid.Monoid[B]) Kleisli[R, E, []A, B] {
+	return TraverseReduceArray(trfrm, m.Concat, m.Empty())
+}

v2/readerioresult/array.go

@@ -0,0 +1,296 @@
+// 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 readerioresult
+
+import (
+	"github.com/IBM/fp-go/v2/function"
+	RA "github.com/IBM/fp-go/v2/internal/array"
+	"github.com/IBM/fp-go/v2/monoid"
+)
+
+// MonadReduceArray reduces an array of ReaderIOResults to a single ReaderIOResult by applying a reduction function.
+// This is the monadic version that takes the array of ReaderIOResults as the first parameter.
+//
+// Each ReaderIOResult is evaluated with the same environment R, and the results are accumulated using
+// the provided reduce function starting from the initial value. If any ReaderIOResult fails, the entire
+// operation fails with that error.
+//
+// Parameters:
+//   - as: Array of ReaderIOResults to reduce
+//   - reduce: Binary function that combines accumulated value with each ReaderIOResult's result
+//   - initial: Starting value for the reduction
+//
+// Example:
+//
+//	type Config struct { Base int }
+//	readers := []readerioresult.ReaderIOResult[Config, int]{
+//	    readerioresult.Of[Config](func(c Config) int { return c.Base + 1 }),
+//	    readerioresult.Of[Config](func(c Config) int { return c.Base + 2 }),
+//	    readerioresult.Of[Config](func(c Config) int { return c.Base + 3 }),
+//	}
+//	sum := func(acc, val int) int { return acc + val }
+//	r := readerioresult.MonadReduceArray(readers, sum, 0)
+//	result := r(Config{Base: 10})() // result.Of(36) (11 + 12 + 13)
+//
+//go:inline
+func MonadReduceArray[R, A, B any](as []ReaderIOResult[R, A], reduce func(B, A) B, initial B) ReaderIOResult[R, B] {
+	return RA.MonadTraverseReduce(
+		Of,
+		Map,
+		Ap,
+
+		as,
+
+		function.Identity[ReaderIOResult[R, A]],
+		reduce,
+		initial,
+	)
+}
+
+// ReduceArray returns a curried function that reduces an array of ReaderIOResults to a single ReaderIOResult.
+// This is the curried version where the reduction function and initial value are provided first,
+// returning a function that takes the array of ReaderIOResults.
+//
+// Parameters:
+//   - reduce: Binary function that combines accumulated value with each ReaderIOResult's result
+//   - initial: Starting value for the reduction
+//
+// Returns:
+//   - A function that takes an array of ReaderIOResults and returns a ReaderIOResult of the reduced result
+//
+// Example:
+//
+//	type Config struct { Multiplier int }
+//	product := func(acc, val int) int { return acc * val }
+//	reducer := readerioresult.ReduceArray[Config](product, 1)
+//	readers := []readerioresult.ReaderIOResult[Config, int]{
+//	    readerioresult.Of[Config](func(c Config) int { return c.Multiplier * 2 }),
+//	    readerioresult.Of[Config](func(c Config) int { return c.Multiplier * 3 }),
+//	}
+//	r := reducer(readers)
+//	result := r(Config{Multiplier: 5})() // result.Of(150) (10 * 15)
+//
+//go:inline
+func ReduceArray[R, A, B any](reduce func(B, A) B, initial B) Kleisli[R, []ReaderIOResult[R, A], B] {
+	return RA.TraverseReduce[[]ReaderIOResult[R, A]](
+		Of,
+		Map,
+		Ap,
+
+		function.Identity[ReaderIOResult[R, A]],
+		reduce,
+		initial,
+	)
+}
+
+// MonadReduceArrayM reduces an array of ReaderIOResults using a Monoid to combine the results.
+// This is the monadic version that takes the array of ReaderIOResults as the first parameter.
+//
+// The Monoid provides both the binary operation (Concat) and the identity element (Empty)
+// for the reduction, making it convenient when working with monoidal types. If any ReaderIOResult
+// fails, the entire operation fails with that error.
+//
+// Parameters:
+//   - as: Array of ReaderIOResults to reduce
+//   - m: Monoid that defines how to combine the ReaderIOResult results
+//
+// Example:
+//
+//	type Config struct { Factor int }
+//	readers := []readerioresult.ReaderIOResult[Config, int]{
+//	    readerioresult.Of[Config](func(c Config) int { return c.Factor }),
+//	    readerioresult.Of[Config](func(c Config) int { return c.Factor * 2 }),
+//	    readerioresult.Of[Config](func(c Config) int { return c.Factor * 3 }),
+//	}
+//	intAddMonoid := monoid.MakeMonoid(func(a, b int) int { return a + b }, 0)
+//	r := readerioresult.MonadReduceArrayM(readers, intAddMonoid)
+//	result := r(Config{Factor: 5})() // result.Of(30) (5 + 10 + 15)
+//
+//go:inline
+func MonadReduceArrayM[R, A any](as []ReaderIOResult[R, A], m monoid.Monoid[A]) ReaderIOResult[R, A] {
+	return MonadReduceArray(as, m.Concat, m.Empty())
+}
+
+// ReduceArrayM returns a curried function that reduces an array of ReaderIOResults using a Monoid.
+// This is the curried version where the Monoid is provided first, returning a function
+// that takes the array of ReaderIOResults.
+//
+// The Monoid provides both the binary operation (Concat) and the identity element (Empty)
+// for the reduction.
+//
+// Parameters:
+//   - m: Monoid that defines how to combine the ReaderIOResult results
+//
+// Returns:
+//   - A function that takes an array of ReaderIOResults and returns a ReaderIOResult of the reduced result
+//
+// Example:
+//
+//	type Config struct { Scale int }
+//	intMultMonoid := monoid.MakeMonoid(func(a, b int) int { return a * b }, 1)
+//	reducer := readerioresult.ReduceArrayM[Config](intMultMonoid)
+//	readers := []readerioresult.ReaderIOResult[Config, int]{
+//	    readerioresult.Of[Config](func(c Config) int { return c.Scale }),
+//	    readerioresult.Of[Config](func(c Config) int { return c.Scale * 2 }),
+//	}
+//	r := reducer(readers)
+//	result := r(Config{Scale: 3})() // result.Of(18) (3 * 6)
+//
+//go:inline
+func ReduceArrayM[R, A any](m monoid.Monoid[A]) Kleisli[R, []ReaderIOResult[R, A], A] {
+	return ReduceArray[R](m.Concat, m.Empty())
+}
+
+// MonadTraverseReduceArray transforms and reduces an array in one operation.
+// This is the monadic version that takes the array as the first parameter.
+//
+// First, each element is transformed using the provided Kleisli function into a ReaderIOResult.
+// Then, the ReaderIOResult results are reduced using the provided reduction function.
+// If any transformation fails, the entire operation fails with that error.
+//
+// This is more efficient than calling TraverseArray followed by a separate reduce operation,
+// as it combines both operations into a single traversal.
+//
+// Parameters:
+//   - as: Array of elements to transform and reduce
+//   - trfrm: Function that transforms each element into a ReaderIOResult
+//   - reduce: Binary function that combines accumulated value with each transformed result
+//   - initial: Starting value for the reduction
+//
+// Example:
+//
+//	type Config struct { Multiplier int }
+//	numbers := []int{1, 2, 3, 4}
+//	multiply := func(n int) readerioresult.ReaderIOResult[Config, int] {
+//	    return readerioresult.Of[Config](func(c Config) int { return n * c.Multiplier })
+//	}
+//	sum := func(acc, val int) int { return acc + val }
+//	r := readerioresult.MonadTraverseReduceArray(numbers, multiply, sum, 0)
+//	result := r(Config{Multiplier: 10})() // result.Of(100) (10 + 20 + 30 + 40)
+//
+//go:inline
+func MonadTraverseReduceArray[R, A, B, C any](as []A, trfrm Kleisli[R, A, B], reduce func(C, B) C, initial C) ReaderIOResult[R, C] {
+	return RA.MonadTraverseReduce(
+		Of,
+		Map,
+		Ap,
+
+		as,
+
+		trfrm,
+		reduce,
+		initial,
+	)
+}
+
+// TraverseReduceArray returns a curried function that transforms and reduces an array.
+// This is the curried version where the transformation function, reduce function, and initial value
+// are provided first, returning a function that takes the array.
+//
+// First, each element is transformed using the provided Kleisli function into a ReaderIOResult.
+// Then, the ReaderIOResult results are reduced using the provided reduction function.
+//
+// Parameters:
+//   - trfrm: Function that transforms each element into a ReaderIOResult
+//   - reduce: Binary function that combines accumulated value with each transformed result
+//   - initial: Starting value for the reduction
+//
+// Returns:
+//   - A function that takes an array and returns a ReaderIOResult of the reduced result
+//
+// Example:
+//
+//	type Config struct { Base int }
+//	addBase := func(n int) readerioresult.ReaderIOResult[Config, int] {
+//	    return readerioresult.Of[Config](func(c Config) int { return n + c.Base })
+//	}
+//	product := func(acc, val int) int { return acc * val }
+//	transformer := readerioresult.TraverseReduceArray(addBase, product, 1)
+//	r := transformer([]int{2, 3, 4})
+//	result := r(Config{Base: 10})() // result.Of(2184) (12 * 13 * 14)
+//
+//go:inline
+func TraverseReduceArray[R, A, B, C any](trfrm Kleisli[R, A, B], reduce func(C, B) C, initial C) Kleisli[R, []A, C] {
+	return RA.TraverseReduce[[]A](
+		Of,
+		Map,
+		Ap,
+
+		trfrm,
+		reduce,
+		initial,
+	)
+}
+
+// MonadTraverseReduceArrayM transforms and reduces an array using a Monoid.
+// This is the monadic version that takes the array as the first parameter.
+//
+// First, each element is transformed using the provided Kleisli function into a ReaderIOResult.
+// Then, the ReaderIOResult results are reduced using the Monoid's binary operation and identity element.
+// If any transformation fails, the entire operation fails with that error.
+//
+// This combines transformation and monoidal reduction in a single efficient operation.
+//
+// Parameters:
+//   - as: Array of elements to transform and reduce
+//   - trfrm: Function that transforms each element into a ReaderIOResult
+//   - m: Monoid that defines how to combine the transformed results
+//
+// Example:
+//
+//	type Config struct { Offset int }
+//	numbers := []int{1, 2, 3}
+//	addOffset := func(n int) readerioresult.ReaderIOResult[Config, int] {
+//	    return readerioresult.Of[Config](func(c Config) int { return n + c.Offset })
+//	}
+//	intSumMonoid := monoid.MakeMonoid(func(a, b int) int { return a + b }, 0)
+//	r := readerioresult.MonadTraverseReduceArrayM(numbers, addOffset, intSumMonoid)
+//	result := r(Config{Offset: 100})() // result.Of(306) (101 + 102 + 103)
+//
+//go:inline
+func MonadTraverseReduceArrayM[R, A, B any](as []A, trfrm Kleisli[R, A, B], m monoid.Monoid[B]) ReaderIOResult[R, B] {
+	return MonadTraverseReduceArray(as, trfrm, m.Concat, m.Empty())
+}
+
+// TraverseReduceArrayM returns a curried function that transforms and reduces an array using a Monoid.
+// This is the curried version where the transformation function and Monoid are provided first,
+// returning a function that takes the array.
+//
+// First, each element is transformed using the provided Kleisli function into a ReaderIOResult.
+// Then, the ReaderIOResult results are reduced using the Monoid's binary operation and identity element.
+//
+// Parameters:
+//   - trfrm: Function that transforms each element into a ReaderIOResult
+//   - m: Monoid that defines how to combine the transformed results
+//
+// Returns:
+//   - A function that takes an array and returns a ReaderIOResult of the reduced result
+//
+// Example:
+//
+//	type Config struct { Factor int }
+//	scale := func(n int) readerioresult.ReaderIOResult[Config, int] {
+//	    return readerioresult.Of[Config](func(c Config) int { return n * c.Factor })
+//	}
+//	intProdMonoid := monoid.MakeMonoid(func(a, b int) int { return a * b }, 1)
+//	transformer := readerioresult.TraverseReduceArrayM(scale, intProdMonoid)
+//	r := transformer([]int{2, 3, 4})
+//	result := r(Config{Factor: 5})() // result.Of(3000) (10 * 15 * 20)
+//
+//go:inline
+func TraverseReduceArrayM[R, A, B any](trfrm Kleisli[R, A, B], m monoid.Monoid[B]) Kleisli[R, []A, B] {
+	return TraverseReduceArray(trfrm, m.Concat, m.Empty())
+}

v2/readerioresult/array_test.go

@@ -24,6 +24,7 @@ import (
 	A "github.com/IBM/fp-go/v2/array"
 	F "github.com/IBM/fp-go/v2/function"
 	TST "github.com/IBM/fp-go/v2/internal/testing"
+	M "github.com/IBM/fp-go/v2/monoid"
 	"github.com/IBM/fp-go/v2/result"
 	"github.com/stretchr/testify/assert"
 )
@@ -73,3 +74,341 @@ func TestSequenceArrayError(t *testing.T) {
 	// run across four bits
 	s(4)(t)
 }
+
+func TestMonadReduceArray(t *testing.T) {
+	type Config struct{ Base int }
+	config := Config{Base: 10}
+
+	readers := []ReaderIOResult[Config, int]{
+		Of[Config](11),
+		Of[Config](12),
+		Of[Config](13),
+	}
+
+	sum := func(acc, val int) int { return acc + val }
+	r := MonadReduceArray(readers, sum, 0)
+	res := r(config)()
+
+	assert.Equal(t, result.Of(36), res) // 11 + 12 + 13
+}
+
+func TestMonadReduceArrayWithError(t *testing.T) {
+	type Config struct{ Base int }
+	config := Config{Base: 10}
+
+	testErr := errors.New("test error")
+	readers := []ReaderIOResult[Config, int]{
+		Of[Config](11),
+		Left[Config, int](testErr),
+		Of[Config](13),
+	}
+
+	sum := func(acc, val int) int { return acc + val }
+	r := MonadReduceArray(readers, sum, 0)
+	res := r(config)()
+
+	assert.True(t, result.IsLeft(res))
+	val, err := result.Unwrap(res)
+	assert.Equal(t, 0, val)
+	assert.Equal(t, testErr, err)
+}
+
+func TestReduceArray(t *testing.T) {
+	type Config struct{ Multiplier int }
+	config := Config{Multiplier: 5}
+
+	product := func(acc, val int) int { return acc * val }
+	reducer := ReduceArray[Config](product, 1)
+
+	readers := []ReaderIOResult[Config, int]{
+		Of[Config](10),
+		Of[Config](15),
+	}
+
+	r := reducer(readers)
+	res := r(config)()
+
+	assert.Equal(t, result.Of(150), res) // 10 * 15
+}
+
+func TestReduceArrayWithError(t *testing.T) {
+	type Config struct{ Multiplier int }
+	config := Config{Multiplier: 5}
+
+	testErr := errors.New("multiplication error")
+	product := func(acc, val int) int { return acc * val }
+	reducer := ReduceArray[Config](product, 1)
+
+	readers := []ReaderIOResult[Config, int]{
+		Of[Config](10),
+		Left[Config, int](testErr),
+	}
+
+	r := reducer(readers)
+	res := r(config)()
+
+	assert.True(t, result.IsLeft(res))
+	_, err := result.Unwrap(res)
+	assert.Equal(t, testErr, err)
+}
+
+func TestMonadReduceArrayM(t *testing.T) {
+	type Config struct{ Factor int }
+	config := Config{Factor: 5}
+
+	readers := []ReaderIOResult[Config, int]{
+		Of[Config](5),
+		Of[Config](10),
+		Of[Config](15),
+	}
+
+	intAddMonoid := M.MakeMonoid(func(a, b int) int { return a + b }, 0)
+	r := MonadReduceArrayM(readers, intAddMonoid)
+	res := r(config)()
+
+	assert.Equal(t, result.Of(30), res) // 5 + 10 + 15
+}
+
+func TestMonadReduceArrayMWithError(t *testing.T) {
+	type Config struct{ Factor int }
+	config := Config{Factor: 5}
+
+	testErr := errors.New("monoid error")
+	readers := []ReaderIOResult[Config, int]{
+		Of[Config](5),
+		Left[Config, int](testErr),
+		Of[Config](15),
+	}
+
+	intAddMonoid := M.MakeMonoid(func(a, b int) int { return a + b }, 0)
+	r := MonadReduceArrayM(readers, intAddMonoid)
+	res := r(config)()
+
+	assert.True(t, result.IsLeft(res))
+	_, err := result.Unwrap(res)
+	assert.Equal(t, testErr, err)
+}
+
+func TestReduceArrayM(t *testing.T) {
+	type Config struct{ Scale int }
+	config := Config{Scale: 3}
+
+	intMultMonoid := M.MakeMonoid(func(a, b int) int { return a * b }, 1)
+	reducer := ReduceArrayM[Config](intMultMonoid)
+
+	readers := []ReaderIOResult[Config, int]{
+		Of[Config](3),
+		Of[Config](6),
+	}
+
+	r := reducer(readers)
+	res := r(config)()
+
+	assert.Equal(t, result.Of(18), res) // 3 * 6
+}
+
+func TestReduceArrayMWithError(t *testing.T) {
+	type Config struct{ Scale int }
+	config := Config{Scale: 3}
+
+	testErr := errors.New("scale error")
+	intMultMonoid := M.MakeMonoid(func(a, b int) int { return a * b }, 1)
+	reducer := ReduceArrayM[Config](intMultMonoid)
+
+	readers := []ReaderIOResult[Config, int]{
+		Of[Config](3),
+		Left[Config, int](testErr),
+	}
+
+	r := reducer(readers)
+	res := r(config)()
+
+	assert.True(t, result.IsLeft(res))
+	_, err := result.Unwrap(res)
+	assert.Equal(t, testErr, err)
+}
+
+func TestMonadTraverseReduceArray(t *testing.T) {
+	type Config struct{ Multiplier int }
+	config := Config{Multiplier: 10}
+
+	numbers := []int{1, 2, 3, 4}
+	multiply := func(n int) ReaderIOResult[Config, int] {
+		return Of[Config](n * 10)
+	}
+
+	sum := func(acc, val int) int { return acc + val }
+	r := MonadTraverseReduceArray(numbers, multiply, sum, 0)
+	res := r(config)()
+
+	assert.Equal(t, result.Of(100), res) // 10 + 20 + 30 + 40
+}
+
+func TestMonadTraverseReduceArrayWithError(t *testing.T) {
+	type Config struct{ Multiplier int }
+	config := Config{Multiplier: 10}
+
+	testErr := errors.New("transform error")
+	numbers := []int{1, 2, 3, 4}
+	multiply := func(n int) ReaderIOResult[Config, int] {
+		if n == 3 {
+			return Left[Config, int](testErr)
+		}
+		return Of[Config](n * 10)
+	}
+
+	sum := func(acc, val int) int { return acc + val }
+	r := MonadTraverseReduceArray(numbers, multiply, sum, 0)
+	res := r(config)()
+
+	assert.True(t, result.IsLeft(res))
+	_, err := result.Unwrap(res)
+	assert.Equal(t, testErr, err)
+}
+
+func TestTraverseReduceArray(t *testing.T) {
+	type Config struct{ Base int }
+	config := Config{Base: 10}
+
+	addBase := func(n int) ReaderIOResult[Config, int] {
+		return Of[Config](n + 10)
+	}
+
+	product := func(acc, val int) int { return acc * val }
+	transformer := TraverseReduceArray(addBase, product, 1)
+
+	r := transformer([]int{2, 3, 4})
+	res := r(config)()
+
+	assert.Equal(t, result.Of(2184), res) // 12 * 13 * 14
+}
+
+func TestTraverseReduceArrayWithError(t *testing.T) {
+	type Config struct{ Base int }
+	config := Config{Base: 10}
+
+	testErr := errors.New("addition error")
+	addBase := func(n int) ReaderIOResult[Config, int] {
+		if n == 3 {
+			return Left[Config, int](testErr)
+		}
+		return Of[Config](n + 10)
+	}
+
+	product := func(acc, val int) int { return acc * val }
+	transformer := TraverseReduceArray(addBase, product, 1)
+
+	r := transformer([]int{2, 3, 4})
+	res := r(config)()
+
+	assert.True(t, result.IsLeft(res))
+	_, err := result.Unwrap(res)
+	assert.Equal(t, testErr, err)
+}
+
+func TestMonadTraverseReduceArrayM(t *testing.T) {
+	type Config struct{ Offset int }
+	config := Config{Offset: 100}
+
+	numbers := []int{1, 2, 3}
+	addOffset := func(n int) ReaderIOResult[Config, int] {
+		return Of[Config](n + 100)
+	}
+
+	intSumMonoid := M.MakeMonoid(func(a, b int) int { return a + b }, 0)
+	r := MonadTraverseReduceArrayM(numbers, addOffset, intSumMonoid)
+	res := r(config)()
+
+	assert.Equal(t, result.Of(306), res) // 101 + 102 + 103
+}
+
+func TestMonadTraverseReduceArrayMWithError(t *testing.T) {
+	type Config struct{ Offset int }
+	config := Config{Offset: 100}
+
+	testErr := errors.New("offset error")
+	numbers := []int{1, 2, 3}
+	addOffset := func(n int) ReaderIOResult[Config, int] {
+		if n == 2 {
+			return Left[Config, int](testErr)
+		}
+		return Of[Config](n + 100)
+	}
+
+	intSumMonoid := M.MakeMonoid(func(a, b int) int { return a + b }, 0)
+	r := MonadTraverseReduceArrayM(numbers, addOffset, intSumMonoid)
+	res := r(config)()
+
+	assert.True(t, result.IsLeft(res))
+	_, err := result.Unwrap(res)
+	assert.Equal(t, testErr, err)
+}
+
+func TestTraverseReduceArrayM(t *testing.T) {
+	type Config struct{ Factor int }
+	config := Config{Factor: 5}
+
+	scale := func(n int) ReaderIOResult[Config, int] {
+		return Of[Config](n * 5)
+	}
+
+	intProdMonoid := M.MakeMonoid(func(a, b int) int { return a * b }, 1)
+	transformer := TraverseReduceArrayM(scale, intProdMonoid)
+	r := transformer([]int{2, 3, 4})
+	res := r(config)()
+
+	assert.Equal(t, result.Of(3000), res) // 10 * 15 * 20
+}
+
+func TestTraverseReduceArrayMWithError(t *testing.T) {
+	type Config struct{ Factor int }
+	config := Config{Factor: 5}
+
+	testErr := errors.New("scaling error")
+	scale := func(n int) ReaderIOResult[Config, int] {
+		if n == 3 {
+			return Left[Config, int](testErr)
+		}
+		return Of[Config](n * 5)
+	}
+
+	intProdMonoid := M.MakeMonoid(func(a, b int) int { return a * b }, 1)
+	transformer := TraverseReduceArrayM(scale, intProdMonoid)
+	r := transformer([]int{2, 3, 4})
+	res := r(config)()
+
+	assert.True(t, result.IsLeft(res))
+	_, err := result.Unwrap(res)
+	assert.Equal(t, testErr, err)
+}
+
+func TestReduceArrayEmptyArray(t *testing.T) {
+	type Config struct{ Base int }
+	config := Config{Base: 10}
+
+	sum := func(acc, val int) int { return acc + val }
+	reducer := ReduceArray[Config](sum, 100)
+
+	readers := []ReaderIOResult[Config, int]{}
+	r := reducer(readers)
+	res := r(config)()
+
+	assert.Equal(t, result.Of(100), res) // Should return initial value
+}
+
+func TestTraverseReduceArrayEmptyArray(t *testing.T) {
+	type Config struct{ Base int }
+	config := Config{Base: 10}
+
+	addBase := func(n int) ReaderIOResult[Config, int] {
+		return Of[Config](n + 10)
+	}
+
+	sum := func(acc, val int) int { return acc + val }
+	transformer := TraverseReduceArray(addBase, sum, 50)
+
+	r := transformer([]int{})
+	res := r(config)()
+
+	assert.Equal(t, result.Of(50), res) // Should return initial value
+}

v2/readerresult/benchmark_test.go

@@ -21,6 +21,7 @@ import (
 	"testing"
 
 	F "github.com/IBM/fp-go/v2/function"
+	N "github.com/IBM/fp-go/v2/number"
 )
 
 type BenchContext struct {
@@ -53,7 +54,7 @@ func BenchmarkLeft(b *testing.B) {
 func BenchmarkMap(b *testing.B) {
 	ctx := BenchContext{Value: 42}
 	rr := Of[BenchContext](10)
-	double := func(x int) int { return x * 2 }
+	double := N.Mul(2)
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
 		mapped := F.Pipe1(rr, Map[BenchContext](double))
@@ -64,7 +65,7 @@ func BenchmarkMap(b *testing.B) {
 func BenchmarkMapChain(b *testing.B) {
 	ctx := BenchContext{Value: 42}
 	rr := Of[BenchContext](1)
-	double := func(x int) int { return x * 2 }
+	double := N.Mul(2)
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
 		result := F.Pipe3(
@@ -112,7 +113,7 @@ func BenchmarkChainDeep(b *testing.B) {
 
 func BenchmarkAp(b *testing.B) {
 	ctx := BenchContext{Value: 42}
-	fab := Of[BenchContext](func(x int) int { return x * 2 })
+	fab := Of[BenchContext](N.Mul(2))
 	fa := Of[BenchContext](21)
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
@@ -191,7 +192,7 @@ func BenchmarkErrorPropagation(b *testing.B) {
 	ctx := BenchContext{Value: 42}
 	err := benchError
 	rr := Left[BenchContext, int](err)
-	double := func(x int) int { return x * 2 }
+	double := N.Mul(2)
 
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {

v2/readerresult/idiomatic_test.go

@@ -23,6 +23,7 @@ import (
 	F "github.com/IBM/fp-go/v2/function"
 	RRI "github.com/IBM/fp-go/v2/idiomatic/readerresult"
 	"github.com/IBM/fp-go/v2/internal/utils"
+	N "github.com/IBM/fp-go/v2/number"
 	L "github.com/IBM/fp-go/v2/optics/lens"
 	"github.com/IBM/fp-go/v2/result"
 	"github.com/stretchr/testify/assert"
@@ -828,7 +829,7 @@ func TestMonadApResult(t *testing.T) {
 	})
 
 	t.Run("value is error", func(t *testing.T) {
-		double := func(x int) int { return x * 2 }
+		double := N.Mul(2)
 		fabr := Of[MyContext](double)
 		fa := result.Left[int](idiomaticTestError)
 		res := MonadApResult(fabr, fa)
@@ -876,7 +877,7 @@ func TestApResult(t *testing.T) {
 	})
 
 	t.Run("with triple composition", func(t *testing.T) {
-		triple := func(x int) int { return x * 3 }
+		triple := N.Mul(3)
 		fa := result.Of(7)
 		res := F.Pipe1(
 			Of[MyContext](triple),
@@ -927,7 +928,7 @@ func TestApResultI(t *testing.T) {
 			return 0, errors.New("parse error")
 		}
 
-		addTen := func(x int) int { return x + 10 }
+		addTen := N.Add(10)
 
 		t.Run("parse success", func(t *testing.T) {
 			value, err := parseValue("42")

v2/readerresult/reader.go

@@ -169,7 +169,7 @@ func FromReader[R, A any](r Reader[R, A]) ReaderResult[R, A] {
 // Example:
 //
 //	rr := readerresult.Of[Config](5)
-//	doubled := readerresult.MonadMap(rr, func(x int) int { return x * 2 })
+//	doubled := readerresult.MonadMap(rr, N.Mul(2))
 //	// doubled(cfg) returns result.Of(10)
 //
 //go:inline
@@ -182,7 +182,7 @@ func MonadMap[R, A, B any](fa ReaderResult[R, A], f func(A) B) ReaderResult[R, B
 //
 // Example:
 //
-//	double := readerresult.Map[Config](func(x int) int { return x * 2 })
+//	double := readerresult.Map[Config](N.Mul(2))
 //	result := F.Pipe1(readerresult.Of[Config](5), double)
 //
 //go:inline
@@ -684,7 +684,7 @@ func FlattenI[R, A any](mma ReaderResult[R, RRI.ReaderResult[R, A]]) ReaderResul
 // Example:
 //
 //	enrichErr := func(e error) error { return fmt.Errorf("enriched: %w", e) }
-//	double := func(x int) int { return x * 2 }
+//	double := N.Mul(2)
 //	result := readerresult.MonadBiMap(rr, enrichErr, double)
 //
 //go:inline
@@ -698,7 +698,7 @@ func MonadBiMap[R, A, B any](fa ReaderResult[R, A], f Endomorphism[error], g fun
 // Example:
 //
 //	enrichErr := func(e error) error { return fmt.Errorf("enriched: %w", e) }
-//	double := func(x int) int { return x * 2 }
+//	double := N.Mul(2)
 //	result := F.Pipe1(rr, readerresult.BiMap[Config](enrichErr, double))
 //
 //go:inline
@@ -742,7 +742,7 @@ func Read[A, R any](r R) func(ReaderResult[R, A]) Result[A] {
 //
 // Example:
 //
-//	fabr := readerresult.Of[Config](func(x int) int { return x * 2 })
+//	fabr := readerresult.Of[Config](N.Mul(2))
 //	result := readerresult.MonadFlap(fabr, 5)  // Returns Of(10)
 //
 //go:inline

v2/readerresult/reader_test.go

@@ -22,6 +22,7 @@ import (
 
 	F "github.com/IBM/fp-go/v2/function"
 	"github.com/IBM/fp-go/v2/internal/utils"
+	N "github.com/IBM/fp-go/v2/number"
 	"github.com/IBM/fp-go/v2/option"
 	"github.com/IBM/fp-go/v2/reader"
 	"github.com/IBM/fp-go/v2/result"
@@ -99,7 +100,7 @@ func TestMap(t *testing.T) {
 
 func TestMonadMap(t *testing.T) {
 	rr := Of[MyContext](5)
-	doubled := MonadMap(rr, func(x int) int { return x * 2 })
+	doubled := MonadMap(rr, N.Mul(2))
 	assert.Equal(t, result.Of(10), doubled(defaultContext))
 }
 
@@ -278,7 +279,7 @@ func TestFlatten(t *testing.T) {
 
 func TestBiMap(t *testing.T) {
 	enrichErr := func(e error) error { return fmt.Errorf("enriched: %w", e) }
-	double := func(x int) int { return x * 2 }
+	double := N.Mul(2)
 
 	res1 := F.Pipe1(Of[MyContext](5), BiMap[MyContext](enrichErr, double))(defaultContext)
 	assert.Equal(t, result.Of(10), res1)
@@ -308,7 +309,7 @@ func TestRead(t *testing.T) {
 }
 
 func TestFlap(t *testing.T) {
-	fabr := Of[MyContext](func(x int) int { return x * 2 })
+	fabr := Of[MyContext](N.Mul(2))
 	flapped := MonadFlap(fabr, 5)
 	assert.Equal(t, result.Of(10), flapped(defaultContext))
 }

v2/statereaderioeither/state.go

@@ -66,7 +66,7 @@ func Of[S, R, E, A any](a A) StateReaderIOEither[S, R, E, A] {
 //
 //	result := statereaderioeither.MonadMap(
 //	    statereaderioeither.Of[AppState, Config, error](21),
-//	    func(x int) int { return x * 2 },
+//	    N.Mul(2),
 //	) // Result contains 42
 func MonadMap[S, R, E, A, B any](fa StateReaderIOEither[S, R, E, A], f func(A) B) StateReaderIOEither[S, R, E, B] {
 	return statet.MonadMap[StateReaderIOEither[S, R, E, A], StateReaderIOEither[S, R, E, B]](
@@ -81,7 +81,7 @@ func MonadMap[S, R, E, A, B any](fa StateReaderIOEither[S, R, E, A], f func(A) B
 //
 // Example:
 //
-//	double := statereaderioeither.Map[AppState, Config, error](func(x int) int { return x * 2 })
+//	double := statereaderioeither.Map[AppState, Config, error](N.Mul(2))
 //	result := function.Pipe1(statereaderioeither.Of[AppState, Config, error](21), double)
 func Map[S, R, E, A, B any](f func(A) B) Operator[S, R, E, A, B] {
 	return statet.Map[StateReaderIOEither[S, R, E, A], StateReaderIOEither[S, R, E, B]](
@@ -133,7 +133,7 @@ func Chain[S, R, E, A, B any](f Kleisli[S, R, E, A, B]) Operator[S, R, E, A, B]
 //
 // Example:
 //
-//	fab := statereaderioeither.Of[AppState, Config, error](func(x int) int { return x * 2 })
+//	fab := statereaderioeither.Of[AppState, Config, error](N.Mul(2))
 //	fa := statereaderioeither.Of[AppState, Config, error](21)
 //	result := statereaderioeither.MonadAp(fab, fa) // Result contains 42
 func MonadAp[B, S, R, E, A any](fab StateReaderIOEither[S, R, E, func(A) B], fa StateReaderIOEither[S, R, E, A]) StateReaderIOEither[S, R, E, B] {

v2/statereaderioeither/statereaderioeither_test.go

@@ -252,7 +252,7 @@ func TestFromState(t *testing.T) {
 
 	assert.True(t, E.IsRight(res))
 	E.Map[error](func(p P.Pair[testState, int]) P.Pair[testState, int] {
-		assert.Equal(t, 11, P.Tail(p)) // Incremented value
+		assert.Equal(t, 11, P.Tail(p))         // Incremented value
 		assert.Equal(t, 11, P.Head(p).counter) // State updated
 		return p
 	})(res)
@@ -568,7 +568,7 @@ func TestStatefulComputation(t *testing.T) {
 	res := result(initialState)(ctx)()
 	assert.True(t, E.IsRight(res))
 	E.Map[error](func(p P.Pair[testState, int]) P.Pair[testState, int] {
-		assert.Equal(t, 3, P.Tail(p)) // Last incremented value
+		assert.Equal(t, 3, P.Tail(p))         // Last incremented value
 		assert.Equal(t, 3, P.Head(p).counter) // State updated three times
 		return p
 	})(res)