fix: logging implementation for context sensitive operations

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

.github/workflows/build.yml

@@ -134,7 +134,7 @@ jobs:
           fetch-depth: 0
 
       - name: Set up Node.js ${{ env.NODE_VERSION }}
-        uses: actions/setup-node@6044e13b5dc448c55e2357c09f80417699197238 # v6.2.0
+        uses: actions/setup-node@53b83947a5a98c8d113130e565377fae1a50d02f # v6.3.0
         with:
           node-version: ${{ env.NODE_VERSION }}
 

context7.json

@@ -0,0 +1,4 @@
+{
+  "url": "https://context7.com/ibm/fp-go",
+  "public_key": "pk_7wJdJRn8zGHxvIYu7eh9h"
+}

v2/README.md

@@ -3,6 +3,7 @@
 [![Go Reference](https://pkg.go.dev/badge/github.com/IBM/fp-go/v2.svg)](https://pkg.go.dev/github.com/IBM/fp-go/v2)
 [![Coverage Status](https://coveralls.io/repos/github/IBM/fp-go/badge.svg?branch=main&flag=v2)](https://coveralls.io/github/IBM/fp-go?branch=main)
 [![Go Report Card](https://goreportcard.com/badge/github.com/IBM/fp-go/v2)](https://goreportcard.com/report/github.com/IBM/fp-go/v2)
+[![Context7](https://img.shields.io/badge/context7-docs-blue)](https://context7.com/ibm/fp-go)
 
 **fp-go** is a comprehensive functional programming library for Go, bringing type-safe functional patterns inspired by [fp-ts](https://gcanti.github.io/fp-ts/) to the Go ecosystem. Version 2 leverages [generic type aliases](https://github.com/golang/go/issues/46477) introduced in Go 1.24, providing a more ergonomic and streamlined API.
 

v2/context/readerio/bracket.go

@@ -1,6 +1,7 @@
 package readerio
 
 import (
+	"github.com/IBM/fp-go/v2/function"
 	RIO "github.com/IBM/fp-go/v2/readerio"
 )
 
@@ -73,3 +74,117 @@ func Bracket[
 ) ReaderIO[B] {
 	return RIO.Bracket(acquire, use, release)
 }
+
+// WithResource creates a higher-order function that manages a resource lifecycle for any operation.
+// It returns a Kleisli arrow that takes a use function and automatically handles resource
+// acquisition and cleanup using the bracket pattern.
+//
+// This is a more composable alternative to Bracket, allowing you to define resource management
+// once and reuse it with different use functions. The resource is acquired when the returned
+// Kleisli arrow is invoked, used by the provided function, and then released regardless of
+// success or failure.
+//
+// Type Parameters:
+//   - A: The type of the resource to be managed
+//   - B: The type of the result produced by the use function
+//   - ANY: The type returned by the release function (typically ignored)
+//
+// Parameters:
+//   - onCreate: A ReaderIO that acquires/creates the resource
+//   - onRelease: A Kleisli arrow that releases/cleans up the resource
+//
+// Returns:
+//   - A Kleisli arrow that takes a use function and returns a ReaderIO managing the full lifecycle
+//
+// Example with database connection:
+//
+//	// Define resource management once
+//	withDB := WithResource(
+//	    // Acquire connection
+//	    func(ctx context.Context) IO[*sql.DB] {
+//	        return func() *sql.DB {
+//	            db, _ := sql.Open("postgres", "connection-string")
+//	            return db
+//	        }
+//	    },
+//	    // Release connection
+//	    func(db *sql.DB) ReaderIO[any] {
+//	        return func(ctx context.Context) IO[any] {
+//	            return func() any {
+//	                db.Close()
+//	                return nil
+//	            }
+//	        }
+//	    },
+//	)
+//
+//	// Reuse with different operations
+//	queryUsers := withDB(func(db *sql.DB) ReaderIO[[]User] {
+//	    return func(ctx context.Context) IO[[]User] {
+//	        return func() []User {
+//	            // Query users from db
+//	            return users
+//	        }
+//	    }
+//	})
+//
+//	insertUser := withDB(func(db *sql.DB) ReaderIO[int64] {
+//	    return func(ctx context.Context) IO[int64] {
+//	        return func() int64 {
+//	            // Insert user into db
+//	            return userID
+//	        }
+//	    }
+//	})
+//
+// Example with file handling:
+//
+//	withFile := WithResource(
+//	    func(ctx context.Context) IO[*os.File] {
+//	        return func() *os.File {
+//	            f, _ := os.Open("data.txt")
+//	            return f
+//	        }
+//	    },
+//	    func(f *os.File) ReaderIO[any] {
+//	        return func(ctx context.Context) IO[any] {
+//	            return func() any {
+//	                f.Close()
+//	                return nil
+//	            }
+//	        }
+//	    },
+//	)
+//
+//	// Use for reading
+//	readContent := withFile(func(f *os.File) ReaderIO[string] {
+//	    return func(ctx context.Context) IO[string] {
+//	        return func() string {
+//	            data, _ := io.ReadAll(f)
+//	            return string(data)
+//	        }
+//	    }
+//	})
+//
+//	// Use for getting file info
+//	getSize := withFile(func(f *os.File) ReaderIO[int64] {
+//	    return func(ctx context.Context) IO[int64] {
+//	        return func() int64 {
+//	            info, _ := f.Stat()
+//	            return info.Size()
+//	        }
+//	    }
+//	})
+//
+// Use Cases:
+//   - Database connections: Acquire connection, execute queries, close connection
+//   - File handles: Open file, read/write, close file
+//   - Network connections: Establish connection, transfer data, close connection
+//   - Locks: Acquire lock, perform critical section, release lock
+//   - Temporary resources: Create temp file/directory, use it, clean up
+//
+//go:inline
+func WithResource[A, B, ANY any](
+	onCreate ReaderIO[A], onRelease Kleisli[A, ANY]) Kleisli[Kleisli[A, B], B] {
+	return function.Bind13of3(Bracket[A, B, ANY])(onCreate, function.Ignore2of2[B](onRelease))
+}

v2/context/readerio/bracket_test.go

@@ -0,0 +1,456 @@
+// 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 readerio
+
+import (
+	"context"
+	"errors"
+	"testing"
+
+	"github.com/IBM/fp-go/v2/io"
+	"github.com/stretchr/testify/assert"
+)
+
+// mockResource simulates a resource that tracks its lifecycle
+type mockResource struct {
+	id       int
+	acquired bool
+	released bool
+	used     bool
+}
+
+// TestBracket_Success tests that Bracket properly manages resource lifecycle on success
+func TestBracket_Success(t *testing.T) {
+	resource := &mockResource{id: 1}
+
+	// Acquire resource
+	acquire := func(ctx context.Context) io.IO[*mockResource] {
+		return func() *mockResource {
+			resource.acquired = true
+			return resource
+		}
+	}
+
+	// Use resource
+	use := func(r *mockResource) ReaderIO[string] {
+		return func(ctx context.Context) io.IO[string] {
+			return func() string {
+				r.used = true
+				return "success"
+			}
+		}
+	}
+
+	// Release resource
+	release := func(r *mockResource, result string) ReaderIO[any] {
+		return func(ctx context.Context) io.IO[any] {
+			return func() any {
+				r.released = true
+				return nil
+			}
+		}
+	}
+
+	// Execute bracket
+	operation := Bracket(acquire, use, release)
+	result := operation(context.Background())()
+
+	// Verify lifecycle
+	assert.True(t, resource.acquired, "Resource should be acquired")
+	assert.True(t, resource.used, "Resource should be used")
+	assert.True(t, resource.released, "Resource should be released")
+	assert.Equal(t, "success", result)
+}
+
+// TestBracket_MultipleResources tests managing multiple resources
+func TestBracket_MultipleResources(t *testing.T) {
+	resource1 := &mockResource{id: 1}
+	resource2 := &mockResource{id: 2}
+
+	acquire1 := func(ctx context.Context) io.IO[*mockResource] {
+		return func() *mockResource {
+			resource1.acquired = true
+			return resource1
+		}
+	}
+
+	use1 := func(r1 *mockResource) ReaderIO[*mockResource] {
+		return func(ctx context.Context) io.IO[*mockResource] {
+			return func() *mockResource {
+				r1.used = true
+				resource2.acquired = true
+				return resource2
+			}
+		}
+	}
+
+	release1 := func(r1 *mockResource, result string) ReaderIO[any] {
+		return func(ctx context.Context) io.IO[any] {
+			return func() any {
+				r1.released = true
+				return nil
+			}
+		}
+	}
+
+	// Nested bracket for second resource
+	use2 := func(r2 *mockResource) ReaderIO[string] {
+		return func(ctx context.Context) io.IO[string] {
+			return func() string {
+				r2.used = true
+				return "both used"
+			}
+		}
+	}
+
+	release2 := func(r2 *mockResource, result string) ReaderIO[any] {
+		return func(ctx context.Context) io.IO[any] {
+			return func() any {
+				r2.released = true
+				return nil
+			}
+		}
+	}
+
+	// Compose brackets
+	operation := Bracket(acquire1, func(r1 *mockResource) ReaderIO[string] {
+		return func(ctx context.Context) io.IO[string] {
+			r2 := use1(r1)(ctx)()
+			return Bracket(
+				func(ctx context.Context) io.IO[*mockResource] {
+					return func() *mockResource { return r2 }
+				},
+				use2,
+				release2,
+			)(ctx)
+		}
+	}, release1)
+
+	result := operation(context.Background())()
+
+	assert.True(t, resource1.acquired)
+	assert.True(t, resource1.used)
+	assert.True(t, resource1.released)
+	assert.True(t, resource2.acquired)
+	assert.True(t, resource2.used)
+	assert.True(t, resource2.released)
+	assert.Equal(t, "both used", result)
+}
+
+// TestWithResource_Success tests WithResource with successful operation
+func TestWithResource_Success(t *testing.T) {
+	resource := &mockResource{id: 1}
+
+	// Define resource management
+	withResource := WithResource[*mockResource, string, any](
+		func(ctx context.Context) io.IO[*mockResource] {
+			return func() *mockResource {
+				resource.acquired = true
+				return resource
+			}
+		},
+		func(r *mockResource) ReaderIO[any] {
+			return func(ctx context.Context) io.IO[any] {
+				return func() any {
+					r.released = true
+					return nil
+				}
+			}
+		},
+	)
+
+	// Use resource
+	operation := withResource(func(r *mockResource) ReaderIO[string] {
+		return func(ctx context.Context) io.IO[string] {
+			return func() string {
+				r.used = true
+				return "result"
+			}
+		}
+	})
+
+	result := operation(context.Background())()
+
+	assert.True(t, resource.acquired)
+	assert.True(t, resource.used)
+	assert.True(t, resource.released)
+	assert.Equal(t, "result", result)
+}
+
+// TestWithResource_Reusability tests that WithResource can be reused with different operations
+func TestWithResource_Reusability(t *testing.T) {
+	callCount := 0
+
+	withResource := WithResource[*mockResource, int, any](
+		func(ctx context.Context) io.IO[*mockResource] {
+			return func() *mockResource {
+				callCount++
+				return &mockResource{id: callCount, acquired: true}
+			}
+		},
+		func(r *mockResource) ReaderIO[any] {
+			return func(ctx context.Context) io.IO[any] {
+				return func() any {
+					r.released = true
+					return nil
+				}
+			}
+		},
+	)
+
+	// First operation
+	op1 := withResource(func(r *mockResource) ReaderIO[int] {
+		return func(ctx context.Context) io.IO[int] {
+			return func() int {
+				r.used = true
+				return r.id * 2
+			}
+		}
+	})
+
+	result1 := op1(context.Background())()
+	assert.Equal(t, 2, result1)
+	assert.Equal(t, 1, callCount)
+
+	// Second operation (should create new resource)
+	op2 := withResource(func(r *mockResource) ReaderIO[int] {
+		return func(ctx context.Context) io.IO[int] {
+			return func() int {
+				r.used = true
+				return r.id * 3
+			}
+		}
+	})
+
+	result2 := op2(context.Background())()
+	assert.Equal(t, 6, result2)
+	assert.Equal(t, 2, callCount)
+}
+
+// TestWithResource_DifferentResultTypes tests WithResource with different result types
+func TestWithResource_DifferentResultTypes(t *testing.T) {
+	resource := &mockResource{id: 42}
+
+	withResourceInt := WithResource[*mockResource, int, any](
+		func(ctx context.Context) io.IO[*mockResource] {
+			return func() *mockResource {
+				resource.acquired = true
+				return resource
+			}
+		},
+		func(r *mockResource) ReaderIO[any] {
+			return func(ctx context.Context) io.IO[any] {
+				return func() any {
+					r.released = true
+					return nil
+				}
+			}
+		},
+	)
+
+	// Operation returning int
+	opInt := withResourceInt(func(r *mockResource) ReaderIO[int] {
+		return func(ctx context.Context) io.IO[int] {
+			return func() int {
+				return r.id
+			}
+		}
+	})
+
+	resultInt := opInt(context.Background())()
+	assert.Equal(t, 42, resultInt)
+
+	// Reset resource state
+	resource.acquired = false
+	resource.released = false
+
+	// Create new WithResource for string type
+	withResourceString := WithResource[*mockResource, string, any](
+		func(ctx context.Context) io.IO[*mockResource] {
+			return func() *mockResource {
+				resource.acquired = true
+				return resource
+			}
+		},
+		func(r *mockResource) ReaderIO[any] {
+			return func(ctx context.Context) io.IO[any] {
+				return func() any {
+					r.released = true
+					return nil
+				}
+			}
+		},
+	)
+
+	// Operation returning string
+	opString := withResourceString(func(r *mockResource) ReaderIO[string] {
+		return func(ctx context.Context) io.IO[string] {
+			return func() string {
+				return "value"
+			}
+		}
+	})
+
+	resultString := opString(context.Background())()
+	assert.Equal(t, "value", resultString)
+	assert.True(t, resource.released)
+}
+
+// TestWithResource_ContextPropagation tests that context is properly propagated
+func TestWithResource_ContextPropagation(t *testing.T) {
+	type contextKey string
+	const key contextKey = "test-key"
+
+	withResource := WithResource[string, string, any](
+		func(ctx context.Context) io.IO[string] {
+			return func() string {
+				value := ctx.Value(key)
+				if value != nil {
+					return value.(string)
+				}
+				return "no-value"
+			}
+		},
+		func(r string) ReaderIO[any] {
+			return func(ctx context.Context) io.IO[any] {
+				return func() any {
+					return nil
+				}
+			}
+		},
+	)
+
+	operation := withResource(func(r string) ReaderIO[string] {
+		return func(ctx context.Context) io.IO[string] {
+			return func() string {
+				return r + "-processed"
+			}
+		}
+	})
+
+	ctx := context.WithValue(context.Background(), key, "test-value")
+	result := operation(ctx)()
+
+	assert.Equal(t, "test-value-processed", result)
+}
+
+// TestWithResource_ErrorInRelease tests behavior when release function encounters an error
+func TestWithResource_ErrorInRelease(t *testing.T) {
+	resource := &mockResource{id: 1}
+	releaseError := errors.New("release failed")
+
+	withResource := WithResource[*mockResource, string, error](
+		func(ctx context.Context) io.IO[*mockResource] {
+			return func() *mockResource {
+				resource.acquired = true
+				return resource
+			}
+		},
+		func(r *mockResource) ReaderIO[error] {
+			return func(ctx context.Context) io.IO[error] {
+				return func() error {
+					r.released = true
+					return releaseError
+				}
+			}
+		},
+	)
+
+	operation := withResource(func(r *mockResource) ReaderIO[string] {
+		return func(ctx context.Context) io.IO[string] {
+			return func() string {
+				r.used = true
+				return "success"
+			}
+		}
+	})
+
+	result := operation(context.Background())()
+
+	// Operation should succeed even if release returns error
+	assert.Equal(t, "success", result)
+	assert.True(t, resource.acquired)
+	assert.True(t, resource.used)
+	assert.True(t, resource.released)
+}
+
+// BenchmarkBracket benchmarks the Bracket function
+func BenchmarkBracket(b *testing.B) {
+	acquire := func(ctx context.Context) io.IO[int] {
+		return func() int {
+			return 42
+		}
+	}
+
+	use := func(n int) ReaderIO[int] {
+		return func(ctx context.Context) io.IO[int] {
+			return func() int {
+				return n * 2
+			}
+		}
+	}
+
+	release := func(n int, result int) ReaderIO[any] {
+		return func(ctx context.Context) io.IO[any] {
+			return func() any {
+				return nil
+			}
+		}
+	}
+
+	operation := Bracket(acquire, use, release)
+	ctx := context.Background()
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		operation(ctx)()
+	}
+}
+
+// BenchmarkWithResource benchmarks the WithResource function
+func BenchmarkWithResource(b *testing.B) {
+	withResource := WithResource[int, int, any](
+		func(ctx context.Context) io.IO[int] {
+			return func() int {
+				return 42
+			}
+		},
+		func(n int) ReaderIO[any] {
+			return func(ctx context.Context) io.IO[any] {
+				return func() any {
+					return nil
+				}
+			}
+		},
+	)
+
+	operation := withResource(func(n int) ReaderIO[int] {
+		return func(ctx context.Context) io.IO[int] {
+			return func() int {
+				return n * 2
+			}
+		}
+	})
+
+	ctx := context.Background()
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		operation(ctx)()
+	}
+}
+
+// Made with Bob

v2/context/readerio/profunctor.go

@@ -19,6 +19,8 @@ import (
 	"context"
 
 	"github.com/IBM/fp-go/v2/function"
+	"github.com/IBM/fp-go/v2/io"
+	"github.com/IBM/fp-go/v2/pair"
 )
 
 // Promap is the profunctor map operation that transforms both the input and output of a context-based ReaderIO.
@@ -44,7 +46,7 @@ import (
 //   - An Operator that takes a ReaderIO[A] and returns a ReaderIO[B]
 //
 //go:inline
-func Promap[A, B any](f func(context.Context) (context.Context, context.CancelFunc), g func(A) B) Operator[A, B] {
+func Promap[A, B any](f pair.Kleisli[context.CancelFunc, context.Context, context.Context], g func(A) B) Operator[A, B] {
 	return function.Flow2(
 		Local[A](f),
 		Map(g),
@@ -69,6 +71,76 @@ func Promap[A, B any](f func(context.Context) (context.Context, context.CancelFu
 //   - An Operator that takes a ReaderIO[A] and returns a ReaderIO[A]
 //
 //go:inline
-func Contramap[A any](f func(context.Context) (context.Context, context.CancelFunc)) Operator[A, A] {
+func Contramap[A any](f pair.Kleisli[context.CancelFunc, context.Context, context.Context]) Operator[A, A] {
 	return Local[A](f)
 }
+
+// LocalIOK transforms the context using an IO effect before passing it to a ReaderIO computation.
+//
+// This is similar to Local, but the context transformation itself is wrapped in an IO effect,
+// allowing for side-effectful context transformations. The transformation function receives
+// the current context and returns an IO effect that produces a new context along with a
+// cancel function. The cancel function is automatically called when the computation completes
+// (via defer), ensuring proper cleanup of resources.
+//
+// This is useful for:
+//   - Context transformations that require side effects (e.g., loading configuration)
+//   - Lazy initialization of context values
+//   - Context transformations that may fail or need to perform I/O
+//   - Composing effectful context setup with computations
+//
+// Type Parameters:
+//   - A: The value type of the ReaderIO
+//
+// Parameters:
+//   - f: An IO Kleisli arrow that transforms the context with side effects
+//
+// Returns:
+//   - An Operator that runs the computation with the effectfully transformed context
+//
+// Example:
+//
+//	import (
+//	    "context"
+//	    G "github.com/IBM/fp-go/v2/io"
+//	    F "github.com/IBM/fp-go/v2/function"
+//	)
+//
+//	// Context transformation with side effects (e.g., loading config)
+//	loadConfig := func(ctx context.Context) G.IO[ContextCancel] {
+//	    return func() ContextCancel {
+//	        // Simulate loading configuration
+//	        config := loadConfigFromFile()
+//	        newCtx := context.WithValue(ctx, "config", config)
+//	        return pair.MakePair[context.CancelFunc](func() {}, newCtx)
+//	    }
+//	}
+//
+//	getValue := readerio.FromReader(func(ctx context.Context) string {
+//	    if cfg := ctx.Value("config"); cfg != nil {
+//	        return cfg.(string)
+//	    }
+//	    return "default"
+//	})
+//
+//	result := F.Pipe1(
+//	    getValue,
+//	    readerio.LocalIOK[string](loadConfig),
+//	)
+//	value := result(t.Context())()  // Loads config and uses it
+//
+// Comparison with Local:
+//   - Local: Takes a pure function that transforms the context
+//   - LocalIOK: Takes an IO effect that transforms the context, allowing side effects
+func LocalIOK[A any](f io.Kleisli[context.Context, ContextCancel]) Operator[A, A] {
+	return func(r ReaderIO[A]) ReaderIO[A] {
+		return func(ctx context.Context) IO[A] {
+			p := f(ctx)
+			return func() A {
+				otherCancel, otherCtx := pair.Unpack(p())
+				defer otherCancel()
+				return r(otherCtx)()
+			}
+		}
+	}
+}

v2/context/readerio/profunctor_test.go

@@ -21,6 +21,7 @@ import (
 	"testing"
 	"time"
 
+	"github.com/IBM/fp-go/v2/pair"
 	"github.com/stretchr/testify/assert"
 )
 
@@ -38,9 +39,9 @@ func TestPromapBasic(t *testing.T) {
 		}
 
 		// Transform context and result
-		addKey := func(ctx context.Context) (context.Context, context.CancelFunc) {
+		addKey := func(ctx context.Context) ContextCancel {
 			newCtx := context.WithValue(ctx, "key", 42)
-			return newCtx, func() {}
+			return pair.MakePair[context.CancelFunc](func() {}, newCtx)
 		}
 		toString := strconv.Itoa
 
@@ -63,9 +64,9 @@ func TestContramapBasic(t *testing.T) {
 			}
 		}
 
-		addKey := func(ctx context.Context) (context.Context, context.CancelFunc) {
+		addKey := func(ctx context.Context) ContextCancel {
 			newCtx := context.WithValue(ctx, "key", 100)
-			return newCtx, func() {}
+			return pair.MakePair[context.CancelFunc](func() {}, newCtx)
 		}
 
 		adapted := Contramap[int](addKey)(getValue)
@@ -85,8 +86,9 @@ func TestLocalBasic(t *testing.T) {
 			}
 		}
 
-		addTimeout := func(ctx context.Context) (context.Context, context.CancelFunc) {
-			return context.WithTimeout(ctx, time.Second)
+		addTimeout := func(ctx context.Context) ContextCancel {
+			newCtx, cancelFct := context.WithTimeout(ctx, time.Second)
+			return pair.MakePair(cancelFct, newCtx)
 		}
 
 		adapted := Local[bool](addTimeout)(getValue)
@@ -95,3 +97,81 @@ func TestLocalBasic(t *testing.T) {
 		assert.True(t, result)
 	})
 }
+
+// TestLocalIOKBasic tests basic LocalIOK functionality
+func TestLocalIOKBasic(t *testing.T) {
+	t.Run("context transformation with IO effect", func(t *testing.T) {
+		getValue := func(ctx context.Context) IO[string] {
+			return func() string {
+				if v := ctx.Value("key"); v != nil {
+					return v.(string)
+				}
+				return "default"
+			}
+		}
+
+		// Context transformation wrapped in IO effect
+		addKeyIO := func(ctx context.Context) IO[ContextCancel] {
+			return func() ContextCancel {
+				// Simulate side effect (e.g., loading config)
+				newCtx := context.WithValue(ctx, "key", "loaded-value")
+				return pair.MakePair[context.CancelFunc](func() {}, newCtx)
+			}
+		}
+
+		adapted := LocalIOK[string](addKeyIO)(getValue)
+		result := adapted(t.Context())()
+
+		assert.Equal(t, "loaded-value", result)
+	})
+
+	t.Run("cleanup function is called", func(t *testing.T) {
+		cleanupCalled := false
+
+		getValue := func(ctx context.Context) IO[int] {
+			return func() int {
+				if v := ctx.Value("value"); v != nil {
+					return v.(int)
+				}
+				return 0
+			}
+		}
+
+		addValueIO := func(ctx context.Context) IO[ContextCancel] {
+			return func() ContextCancel {
+				newCtx := context.WithValue(ctx, "value", 42)
+				cleanup := context.CancelFunc(func() {
+					cleanupCalled = true
+				})
+				return pair.MakePair(cleanup, newCtx)
+			}
+		}
+
+		adapted := LocalIOK[int](addValueIO)(getValue)
+		result := adapted(t.Context())()
+
+		assert.Equal(t, 42, result)
+		assert.True(t, cleanupCalled, "cleanup function should be called")
+	})
+
+	t.Run("works with timeout context", func(t *testing.T) {
+		getValue := func(ctx context.Context) IO[bool] {
+			return func() bool {
+				_, hasDeadline := ctx.Deadline()
+				return hasDeadline
+			}
+		}
+
+		addTimeoutIO := func(ctx context.Context) IO[ContextCancel] {
+			return func() ContextCancel {
+				newCtx, cancelFct := context.WithTimeout(ctx, time.Second)
+				return pair.MakePair(cancelFct, newCtx)
+			}
+		}
+
+		adapted := LocalIOK[bool](addTimeoutIO)(getValue)
+		result := adapted(t.Context())()
+
+		assert.True(t, result, "context should have deadline")
+	})
+}

v2/context/readerio/reader.go

@@ -20,6 +20,7 @@ import (
 	"time"
 
 	"github.com/IBM/fp-go/v2/function"
+	"github.com/IBM/fp-go/v2/pair"
 	"github.com/IBM/fp-go/v2/reader"
 	RIO "github.com/IBM/fp-go/v2/readerio"
 )
@@ -677,11 +678,11 @@ func ReadIO[A any](r IO[context.Context]) func(ReaderIO[A]) IO[A] {
 //	    fetchData,
 //	    withTimeout,
 //	)
-func Local[A any](f func(context.Context) (context.Context, context.CancelFunc)) Operator[A, A] {
+func Local[A any](f pair.Kleisli[context.CancelFunc, context.Context, context.Context]) Operator[A, A] {
 	return func(rr ReaderIO[A]) ReaderIO[A] {
 		return func(ctx context.Context) IO[A] {
 			return func() A {
-				otherCtx, otherCancel := f(ctx)
+				otherCancel, otherCtx := pair.Unpack(f(ctx))
 				defer otherCancel()
 				return rr(otherCtx)()
 			}
@@ -742,8 +743,9 @@ func Local[A any](f func(context.Context) (context.Context, context.CancelFunc))
 //	)
 //	data := result(t.Context())()  // Returns Data{Value: "quick"}
 func WithTimeout[A any](timeout time.Duration) Operator[A, A] {
-	return Local[A](func(ctx context.Context) (context.Context, context.CancelFunc) {
-		return context.WithTimeout(ctx, timeout)
+	return Local[A](func(ctx context.Context) ContextCancel {
+		newCtx, cancelFct := context.WithTimeout(ctx, timeout)
+		return pair.MakePair(cancelFct, newCtx)
 	})
 }
 
@@ -806,8 +808,9 @@ func WithTimeout[A any](timeout time.Duration) Operator[A, A] {
 //	)
 //	data := result(parentCtx)()  // Will use parent's 1-hour deadline
 func WithDeadline[A any](deadline time.Time) Operator[A, A] {
-	return Local[A](func(ctx context.Context) (context.Context, context.CancelFunc) {
-		return context.WithDeadline(ctx, deadline)
+	return Local[A](func(ctx context.Context) ContextCancel {
+		newCtx, cancelFct := context.WithDeadline(ctx, deadline)
+		return pair.MakePair(cancelFct, newCtx)
 	})
 }
 

v2/context/readerio/type.go

@@ -23,6 +23,7 @@ import (
 	"github.com/IBM/fp-go/v2/function"
 	"github.com/IBM/fp-go/v2/io"
 	"github.com/IBM/fp-go/v2/lazy"
+	"github.com/IBM/fp-go/v2/pair"
 	"github.com/IBM/fp-go/v2/predicate"
 	"github.com/IBM/fp-go/v2/reader"
 	"github.com/IBM/fp-go/v2/readerio"
@@ -81,4 +82,15 @@ type (
 	Predicate[A any] = predicate.Predicate[A]
 
 	Void = function.Void
+
+	// Pair represents a tuple of two values of types A and B.
+	// It is used to group two related values together.
+	Pair[A, B any] = pair.Pair[A, B]
+
+	// ContextCancel represents a pair of a cancel function and a context.
+	// It is used in operations that create new contexts with cancellation capabilities.
+	//
+	// The first element is the CancelFunc that should be called to release resources.
+	// The second element is the new Context that was created.
+	ContextCancel = Pair[context.CancelFunc, context.Context]
 )

v2/context/readerioresult/logging.go

@@ -28,6 +28,7 @@ import (
 	"github.com/IBM/fp-go/v2/io"
 	"github.com/IBM/fp-go/v2/logging"
 	"github.com/IBM/fp-go/v2/option"
+	"github.com/IBM/fp-go/v2/pair"
 	"github.com/IBM/fp-go/v2/reader"
 	"github.com/IBM/fp-go/v2/result"
 )
@@ -90,132 +91,7 @@ func withLoggingContext(lctx loggingContext) Endomorphism[context.Context] {
 	return F.Bind2nd(withLoggingContextValue, any(lctx))
 }
 
-// LogEntryExitF creates a customizable operator that wraps a ReaderIOResult computation with entry/exit callbacks.
-//
-// This is a more flexible version of LogEntryExit that allows you to provide custom callbacks for
-// entry and exit events. The onEntry callback receives the current context and can return a modified
-// context (e.g., with additional logging information). The onExit callback receives the computation
-// result and can perform custom logging, metrics collection, or cleanup.
-//
-// The function uses the bracket pattern to ensure that:
-//   - The onEntry callback is executed before the computation starts
-//   - The computation runs with the context returned by onEntry
-//   - The onExit callback is executed after the computation completes (success or failure)
-//   - The original result is preserved and returned unchanged
-//   - Cleanup happens even if the computation fails
-//
-// Type Parameters:
-//   - A: The success type of the ReaderIOResult
-//   - ANY: The return type of the onExit callback (typically any)
-//
-// Parameters:
-//   - onEntry: A ReaderIO that receives the current context and returns a (possibly modified) context.
-//     This is executed before the computation starts. Use this for logging entry, adding context values,
-//     starting timers, or initialization logic.
-//   - onExit: A Kleisli function that receives the Result[A] and returns a ReaderIO[ANY].
-//     This is executed after the computation completes, regardless of success or failure.
-//     Use this for logging exit, recording metrics, cleanup, or finalization logic.
-//
-// Returns:
-//   - An Operator that wraps the ReaderIOResult computation with the custom entry/exit callbacks
-//
-// Example with custom context modification:
-//
-//	type RequestID string
-//
-//	logOp := LogEntryExitF[User, any](
-//	    func(ctx context.Context) IO[context.Context] {
-//	        return func() context.Context {
-//	            reqID := RequestID(uuid.New().String())
-//	            log.Printf("[%s] Starting operation", reqID)
-//	            return context.WithValue(ctx, "requestID", reqID)
-//	        }
-//	    },
-//	    func(res Result[User]) ReaderIO[any] {
-//	        return func(ctx context.Context) IO[any] {
-//	            return func() any {
-//	                reqID := ctx.Value("requestID").(RequestID)
-//	                return F.Pipe1(
-//	                    res,
-//	                    result.Fold(
-//	                        func(err error) any {
-//	                            log.Printf("[%s] Operation failed: %v", reqID, err)
-//	                            return nil
-//	                        },
-//	                        func(_ User) any {
-//	                            log.Printf("[%s] Operation succeeded", reqID)
-//	                            return nil
-//	                        },
-//	                    ),
-//	                )
-//	            }
-//	        }
-//	    },
-//	)
-//
-//	wrapped := logOp(fetchUser(123))
-//
-// Example with metrics collection:
-//
-//	import "github.com/prometheus/client_golang/prometheus"
-//
-//	metricsOp := LogEntryExitF[Response, any](
-//	    func(ctx context.Context) IO[context.Context] {
-//	        return func() context.Context {
-//	            requestCount.WithLabelValues("api_call", "started").Inc()
-//	            return context.WithValue(ctx, "startTime", time.Now())
-//	        }
-//	    },
-//	    func(res Result[Response]) ReaderIO[any] {
-//	        return func(ctx context.Context) IO[any] {
-//	            return func() any {
-//	                startTime := ctx.Value("startTime").(time.Time)
-//	                duration := time.Since(startTime).Seconds()
-//
-//	                return F.Pipe1(
-//	                    res,
-//	                    result.Fold(
-//	                        func(err error) any {
-//	                            requestCount.WithLabelValues("api_call", "error").Inc()
-//	                            requestDuration.WithLabelValues("api_call", "error").Observe(duration)
-//	                            return nil
-//	                        },
-//	                        func(_ Response) any {
-//	                            requestCount.WithLabelValues("api_call", "success").Inc()
-//	                            requestDuration.WithLabelValues("api_call", "success").Observe(duration)
-//	                            return nil
-//	                        },
-//	                    ),
-//	                )
-//	            }
-//	        }
-//	    },
-//	)
-//
-// Use Cases:
-//   - Custom context modification: Adding request IDs, trace IDs, or other context values
-//   - Structured logging: Integration with zap, logrus, or other structured loggers
-//   - Metrics collection: Recording operation durations, success/failure rates
-//   - Distributed tracing: OpenTelemetry, Jaeger integration
-//   - Custom monitoring: Application-specific monitoring and alerting
-//
-// Note: LogEntryExit is implemented using LogEntryExitF with standard logging and context management.
-// Use LogEntryExitF when you need more control over the entry/exit behavior or context modification.
-func LogEntryExitF[A, ANY any](
-	onEntry ReaderIO[context.Context],
-	onExit readerio.Kleisli[Result[A], ANY],
-) Operator[A, A] {
-	bracket := F.Bind13of3(readerio.Bracket[context.Context, Result[A], ANY])(onEntry, func(newCtx context.Context, res Result[A]) ReaderIO[ANY] {
-		return readerio.FromIO(onExit(res)(newCtx)) // Get the exit callback for this result
-	})
-
-	return func(src ReaderIOResult[A]) ReaderIOResult[A] {
-		return bracket(F.Flow2(
-			src,
-			FromIOResult,
-		))
-	}
-}
+func noop() {}
 
 // onEntry creates a ReaderIO that handles the entry logging for an operation.
 // It generates a unique logging ID, captures the start time, and logs the entry message.
@@ -230,15 +106,15 @@ func LogEntryExitF[A, ANY any](
 //   - A ReaderIO that prepares the context with logging information and logs the entry
 func onEntry(
 	logLevel slog.Level,
-	cb func(context.Context) *slog.Logger,
+	cb Reader[context.Context, *slog.Logger],
 	nameAttr slog.Attr,
-) ReaderIO[context.Context] {
+) ReaderIO[ContextCancel] {
 
-	return func(ctx context.Context) IO[context.Context] {
+	return func(ctx context.Context) IO[ContextCancel] {
 		// logger
 		logger := cb(ctx)
 
-		return func() context.Context {
+		return func() ContextCancel {
 			// check if the logger is enabled
 			if logger.Enabled(ctx, logLevel) {
 				// Generate unique logging ID and capture start time
@@ -258,19 +134,23 @@ func onEntry(
 				})
 				withLogger := logging.WithLogger(newLogger)
 
-				return withCtx(withLogger(ctx))
+				return F.Pipe2(
+					ctx,
+					withLogger,
+					pair.Map[context.CancelFunc](withCtx),
+				)
 			}
 			// logging disabled
 			withCtx := withLoggingContext(loggingContext{
 				logger:    logger,
 				isEnabled: false,
 			})
-			return withCtx(ctx)
+			return pair.MakePair[context.CancelFunc](noop, withCtx(ctx))
 		}
 	}
 }
 
-// onExitAny creates a Kleisli function that handles exit logging for an operation.
+// onExitVoid creates a Kleisli function that handles exit logging for an operation.
 // It logs either success or error based on the Result, including the operation duration.
 // Only logs if logging was enabled during entry (checked via loggingContext.isEnabled).
 //
@@ -280,33 +160,33 @@ func onEntry(
 //
 // Returns:
 //   - A Kleisli function that logs the exit/error and returns nil
-func onExitAny(
+func onExitVoid(
 	logLevel slog.Level,
 	nameAttr slog.Attr,
-) readerio.Kleisli[Result[any], any] {
-	return func(res Result[any]) ReaderIO[any] {
-		return func(ctx context.Context) IO[any] {
+) readerio.Kleisli[Result[Void], Void] {
+	return func(res Result[Void]) ReaderIO[Void] {
+		return func(ctx context.Context) IO[Void] {
 			value := getLoggingContext(ctx)
 
 			if value.isEnabled {
 
-				return func() any {
+				return func() Void {
 					// Retrieve logging information from context
 					durationAttr := slog.Duration("duration", time.Since(value.startTime))
 
 					// Log error with ID and duration
-					onError := func(err error) any {
+					onError := func(err error) Void {
 						value.logger.LogAttrs(ctx, logLevel, "[throwing]",
 							nameAttr,
 							durationAttr,
 							slog.Any("error", err))
-						return nil
+						return F.VOID
 					}
 
 					// Log success with ID and duration
-					onSuccess := func(_ any) any {
+					onSuccess := func(v Void) Void {
 						value.logger.LogAttrs(ctx, logLevel, "[exiting ]", nameAttr, durationAttr)
-						return nil
+						return v
 					}
 
 					return F.Pipe1(
@@ -316,7 +196,7 @@ func onExitAny(
 				}
 			}
 			// nothing to do
-			return io.Of[any](nil)
+			return io.Of(F.VOID)
 		}
 	}
 }
@@ -374,13 +254,21 @@ func LogEntryExitWithCallback[A any](
 
 	nameAttr := slog.String("name", name)
 
-	return LogEntryExitF(
+	entry := F.Pipe1(
 		onEntry(logLevel, cb, nameAttr),
-		F.Flow2(
-			result.MapTo[A, any](nil),
-			onExitAny(logLevel, nameAttr),
-		),
+		readerio.LocalIOK[Result[A]],
 	)
+
+	exit := readerio.Tap(F.Flow2(
+		result.MapTo[A](F.VOID),
+		onExitVoid(logLevel, nameAttr),
+	))
+
+	return F.Flow2(
+		exit,
+		entry,
+	)
+
 }
 
 // LogEntryExit creates an operator that logs the entry and exit of a ReaderIOResult computation with timing and correlation IDs.

v2/context/readerioresult/logging_comprehensive_test.go

@@ -0,0 +1,417 @@
+// 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 (
+	"bytes"
+	"errors"
+	"log/slog"
+	"strings"
+	"testing"
+
+	F "github.com/IBM/fp-go/v2/function"
+	"github.com/IBM/fp-go/v2/logging"
+	N "github.com/IBM/fp-go/v2/number"
+	"github.com/IBM/fp-go/v2/result"
+	"github.com/stretchr/testify/assert"
+)
+
+// TestTapSLogComprehensive_Success verifies TapSLog logs successful values
+func TestTapSLogComprehensive_Success(t *testing.T) {
+	var buf bytes.Buffer
+	logger := slog.New(slog.NewTextHandler(&buf, &slog.HandlerOptions{
+		Level: slog.LevelInfo,
+	}))
+	oldLogger := logging.SetLogger(logger)
+	defer logging.SetLogger(oldLogger)
+
+	t.Run("logs integer success value", func(t *testing.T) {
+		buf.Reset()
+
+		pipeline := F.Pipe2(
+			Of(42),
+			TapSLog[int]("Integer value"),
+			Map(N.Mul(2)),
+		)
+
+		res := pipeline(t.Context())()
+
+		// Verify result is correct
+		assert.Equal(t, 84, F.Pipe1(res, getOrZero))
+
+		// Verify logging occurred
+		logOutput := buf.String()
+		assert.Contains(t, logOutput, "Integer value", "Should log the message")
+		assert.Contains(t, logOutput, "value=42", "Should log the success value")
+		assert.NotContains(t, logOutput, "error", "Should not contain error keyword for success")
+	})
+
+	t.Run("logs string success value", func(t *testing.T) {
+		buf.Reset()
+
+		pipeline := F.Pipe1(
+			Of("hello world"),
+			TapSLog[string]("String value"),
+		)
+
+		res := pipeline(t.Context())()
+
+		// Verify result is correct
+		assert.True(t, F.Pipe1(res, isRight[string]))
+
+		// Verify logging occurred
+		logOutput := buf.String()
+		assert.Contains(t, logOutput, "String value")
+		assert.Contains(t, logOutput, `value="hello world"`)
+	})
+
+	t.Run("logs struct success value", func(t *testing.T) {
+		buf.Reset()
+
+		type User struct {
+			ID   int
+			Name string
+		}
+
+		user := User{ID: 123, Name: "Alice"}
+		pipeline := F.Pipe1(
+			Of(user),
+			TapSLog[User]("User struct"),
+		)
+
+		res := pipeline(t.Context())()
+
+		// Verify result is correct
+		assert.True(t, F.Pipe1(res, isRight[User]))
+
+		// Verify logging occurred with struct fields
+		logOutput := buf.String()
+		assert.Contains(t, logOutput, "User struct")
+		assert.Contains(t, logOutput, "ID:123")
+		assert.Contains(t, logOutput, "Name:Alice")
+	})
+
+	t.Run("logs multiple success values in pipeline", func(t *testing.T) {
+		buf.Reset()
+
+		step1 := F.Pipe2(
+			Of(10),
+			TapSLog[int]("Initial value"),
+			Map(N.Mul(2)),
+		)
+
+		pipeline := F.Pipe2(
+			step1,
+			TapSLog[int]("After doubling"),
+			Map(N.Add(5)),
+		)
+
+		res := pipeline(t.Context())()
+
+		// Verify result is correct
+		assert.Equal(t, 25, getOrZero(res))
+
+		// Verify both log entries
+		logOutput := buf.String()
+		assert.Contains(t, logOutput, "Initial value")
+		assert.Contains(t, logOutput, "value=10")
+		assert.Contains(t, logOutput, "After doubling")
+		assert.Contains(t, logOutput, "value=20")
+	})
+}
+
+// TestTapSLogComprehensive_Error verifies TapSLog behavior with errors
+func TestTapSLogComprehensive_Error(t *testing.T) {
+	var buf bytes.Buffer
+	logger := slog.New(slog.NewTextHandler(&buf, &slog.HandlerOptions{
+		Level: slog.LevelInfo,
+	}))
+	oldLogger := logging.SetLogger(logger)
+	defer logging.SetLogger(oldLogger)
+
+	t.Run("logs error values", func(t *testing.T) {
+		buf.Reset()
+
+		testErr := errors.New("test error")
+		pipeline := F.Pipe2(
+			Left[int](testErr),
+			TapSLog[int]("Error case"),
+			Map(N.Mul(2)),
+		)
+
+		res := pipeline(t.Context())()
+
+		// Verify error is preserved
+		assert.True(t, F.Pipe1(res, isLeft[int]))
+
+		// Verify logging occurred for error
+		logOutput := buf.String()
+		assert.Contains(t, logOutput, "Error case", "Should log the message")
+		assert.Contains(t, logOutput, "error", "Should contain error keyword")
+		assert.Contains(t, logOutput, "test error", "Should log the error message")
+		assert.NotContains(t, logOutput, "value=", "Should not log 'value=' for errors")
+	})
+
+	t.Run("preserves error through pipeline", func(t *testing.T) {
+		buf.Reset()
+
+		originalErr := errors.New("original error")
+		step1 := F.Pipe2(
+			Left[int](originalErr),
+			TapSLog[int]("First tap"),
+			Map(N.Mul(2)),
+		)
+
+		pipeline := F.Pipe2(
+			step1,
+			TapSLog[int]("Second tap"),
+			Map(N.Add(5)),
+		)
+
+		res := pipeline(t.Context())()
+
+		// Verify error is preserved
+		assert.True(t, isLeft(res))
+
+		// Verify both taps logged the error
+		logOutput := buf.String()
+		errorCount := strings.Count(logOutput, "original error")
+		assert.Equal(t, 2, errorCount, "Both TapSLog calls should log the error")
+		assert.Contains(t, logOutput, "First tap")
+		assert.Contains(t, logOutput, "Second tap")
+	})
+
+	t.Run("logs error after successful operation", func(t *testing.T) {
+		buf.Reset()
+
+		pipeline := F.Pipe3(
+			Of(10),
+			TapSLog[int]("Before error"),
+			Chain(func(n int) ReaderIOResult[int] {
+				return Left[int](errors.New("chain error"))
+			}),
+			TapSLog[int]("After error"),
+		)
+
+		res := pipeline(t.Context())()
+
+		// Verify error is present
+		assert.True(t, F.Pipe1(res, isLeft[int]))
+
+		// Verify both logs
+		logOutput := buf.String()
+		assert.Contains(t, logOutput, "Before error")
+		assert.Contains(t, logOutput, "value=10")
+		assert.Contains(t, logOutput, "After error")
+		assert.Contains(t, logOutput, "chain error")
+	})
+}
+
+// TestTapSLogComprehensive_EdgeCases verifies TapSLog with edge cases
+func TestTapSLogComprehensive_EdgeCases(t *testing.T) {
+	var buf bytes.Buffer
+	logger := slog.New(slog.NewTextHandler(&buf, &slog.HandlerOptions{
+		Level: slog.LevelInfo,
+	}))
+	oldLogger := logging.SetLogger(logger)
+	defer logging.SetLogger(oldLogger)
+
+	t.Run("logs zero value", func(t *testing.T) {
+		buf.Reset()
+
+		pipeline := F.Pipe1(
+			Of(0),
+			TapSLog[int]("Zero value"),
+		)
+
+		res := pipeline(t.Context())()
+
+		assert.Equal(t, 0, F.Pipe1(res, getOrZero))
+
+		logOutput := buf.String()
+		assert.Contains(t, logOutput, "Zero value")
+		assert.Contains(t, logOutput, "value=0")
+	})
+
+	t.Run("logs empty string", func(t *testing.T) {
+		buf.Reset()
+
+		pipeline := F.Pipe1(
+			Of(""),
+			TapSLog[string]("Empty string"),
+		)
+
+		res := pipeline(t.Context())()
+
+		assert.True(t, F.Pipe1(res, isRight[string]))
+
+		logOutput := buf.String()
+		assert.Contains(t, logOutput, "Empty string")
+		assert.Contains(t, logOutput, `value=""`)
+	})
+
+	t.Run("logs nil pointer", func(t *testing.T) {
+		buf.Reset()
+
+		type Data struct {
+			Value string
+		}
+
+		var nilData *Data
+		pipeline := F.Pipe1(
+			Of(nilData),
+			TapSLog[*Data]("Nil pointer"),
+		)
+
+		res := pipeline(t.Context())()
+
+		assert.True(t, F.Pipe1(res, isRight[*Data]))
+
+		logOutput := buf.String()
+		assert.Contains(t, logOutput, "Nil pointer")
+		// Nil representation may vary, but should be logged
+		assert.NotEmpty(t, logOutput)
+	})
+
+	t.Run("respects logger level - disabled", func(t *testing.T) {
+		buf.Reset()
+
+		// Create logger that only logs errors
+		errorLogger := slog.New(slog.NewTextHandler(&buf, &slog.HandlerOptions{
+			Level: slog.LevelError,
+		}))
+		oldLogger := logging.SetLogger(errorLogger)
+		defer logging.SetLogger(oldLogger)
+
+		pipeline := F.Pipe1(
+			Of(42),
+			TapSLog[int]("Should not log"),
+		)
+
+		res := pipeline(t.Context())()
+
+		assert.Equal(t, 42, F.Pipe1(res, getOrZero))
+
+		// Should have no logs since level is ERROR
+		logOutput := buf.String()
+		assert.Empty(t, logOutput, "Should not log when level is disabled")
+	})
+}
+
+// TestTapSLogComprehensive_Integration verifies TapSLog in realistic scenarios
+func TestTapSLogComprehensive_Integration(t *testing.T) {
+	var buf bytes.Buffer
+	logger := slog.New(slog.NewTextHandler(&buf, &slog.HandlerOptions{
+		Level: slog.LevelInfo,
+	}))
+	oldLogger := logging.SetLogger(logger)
+	defer logging.SetLogger(oldLogger)
+
+	t.Run("complex pipeline with mixed success and error", func(t *testing.T) {
+		buf.Reset()
+
+		// Simulate a data processing pipeline
+		validatePositive := func(n int) ReaderIOResult[int] {
+			if n > 0 {
+				return Of(n)
+			}
+			return Left[int](errors.New("number must be positive"))
+		}
+
+		step1 := F.Pipe3(
+			Of(5),
+			TapSLog[int]("Input received"),
+			Map(N.Mul(2)),
+			TapSLog[int]("After multiplication"),
+		)
+
+		pipeline := F.Pipe2(
+			step1,
+			Chain(validatePositive),
+			TapSLog[int]("After validation"),
+		)
+
+		res := pipeline(t.Context())()
+
+		assert.Equal(t, 10, getOrZero(res))
+
+		logOutput := buf.String()
+		assert.Contains(t, logOutput, "Input received")
+		assert.Contains(t, logOutput, "value=5")
+		assert.Contains(t, logOutput, "After multiplication")
+		assert.Contains(t, logOutput, "value=10")
+		assert.Contains(t, logOutput, "After validation")
+		assert.Contains(t, logOutput, "value=10")
+	})
+
+	t.Run("error propagation with logging", func(t *testing.T) {
+		buf.Reset()
+
+		validatePositive := func(n int) ReaderIOResult[int] {
+			if n > 0 {
+				return Of(n)
+			}
+			return Left[int](errors.New("number must be positive"))
+		}
+
+		step1 := F.Pipe3(
+			Of(-5),
+			TapSLog[int]("Input received"),
+			Map(N.Mul(2)),
+			TapSLog[int]("After multiplication"),
+		)
+
+		pipeline := F.Pipe2(
+			step1,
+			Chain(validatePositive),
+			TapSLog[int]("After validation"),
+		)
+
+		res := pipeline(t.Context())()
+
+		assert.True(t, isLeft(res))
+
+		logOutput := buf.String()
+		// First two taps should log success
+		assert.Contains(t, logOutput, "Input received")
+		assert.Contains(t, logOutput, "value=-5")
+		assert.Contains(t, logOutput, "After multiplication")
+		assert.Contains(t, logOutput, "value=-10")
+		// Last tap should log error
+		assert.Contains(t, logOutput, "After validation")
+		assert.Contains(t, logOutput, "number must be positive")
+	})
+}
+
+// Helper functions for tests
+
+func getOrZero(res Result[int]) int {
+	val, err := result.Unwrap(res)
+	if err == nil {
+		return val
+	}
+	return 0
+}
+
+func isRight[A any](res Result[A]) bool {
+	return result.IsRight(res)
+}
+
+func isLeft[A any](res Result[A]) bool {
+	return result.IsLeft(res)
+}
+
+// Made with Bob

v2/context/readerioresult/logging_test.go

@@ -13,6 +13,7 @@ import (
 	F "github.com/IBM/fp-go/v2/function"
 	"github.com/IBM/fp-go/v2/logging"
 	N "github.com/IBM/fp-go/v2/number"
+	"github.com/IBM/fp-go/v2/pair"
 	"github.com/IBM/fp-go/v2/result"
 	S "github.com/IBM/fp-go/v2/string"
 	"github.com/stretchr/testify/assert"
@@ -53,6 +54,11 @@ func TestLogEntryExitSuccess(t *testing.T) {
 	assert.Contains(t, logOutput, "TestOperation")
 	assert.Contains(t, logOutput, "ID=")
 	assert.Contains(t, logOutput, "duration=")
+
+	// Verify entry log appears before exit log
+	enteringIdx := strings.Index(logOutput, "[entering]")
+	exitingIdx := strings.Index(logOutput, "[exiting ]")
+	assert.Greater(t, exitingIdx, enteringIdx, "Exit log should appear after entry log")
 }
 
 // TestLogEntryExitError tests error operation logging
@@ -81,6 +87,11 @@ func TestLogEntryExitError(t *testing.T) {
 	assert.Contains(t, logOutput, "test error")
 	assert.Contains(t, logOutput, "ID=")
 	assert.Contains(t, logOutput, "duration=")
+
+	// Verify entry log appears before error log
+	enteringIdx := strings.Index(logOutput, "[entering]")
+	throwingIdx := strings.Index(logOutput, "[throwing]")
+	assert.Greater(t, throwingIdx, enteringIdx, "Error log should appear after entry log")
 }
 
 // TestLogEntryExitNested tests nested operations with different IDs
@@ -119,6 +130,48 @@ func TestLogEntryExitNested(t *testing.T) {
 	exitCount := strings.Count(logOutput, "[exiting ]")
 	assert.Equal(t, 2, enterCount, "Should have 2 entering logs")
 	assert.Equal(t, 2, exitCount, "Should have 2 exiting logs")
+
+	// Verify log ordering: Each operation logs entry before exit
+	// Note: Due to Chain semantics, OuterOp completes before InnerOp starts
+	lines := strings.Split(logOutput, "\n")
+	var logSequence []string
+	for _, line := range lines {
+		if strings.Contains(line, "OuterOp") && strings.Contains(line, "[entering]") {
+			logSequence = append(logSequence, "OuterOp-entering")
+		} else if strings.Contains(line, "OuterOp") && strings.Contains(line, "[exiting ]") {
+			logSequence = append(logSequence, "OuterOp-exiting")
+		} else if strings.Contains(line, "InnerOp") && strings.Contains(line, "[entering]") {
+			logSequence = append(logSequence, "InnerOp-entering")
+		} else if strings.Contains(line, "InnerOp") && strings.Contains(line, "[exiting ]") {
+			logSequence = append(logSequence, "InnerOp-exiting")
+		}
+	}
+
+	// Verify each operation's entry comes before its exit
+	assert.Equal(t, 4, len(logSequence), "Should have 4 log entries")
+
+	// Find indices
+	outerEnterIdx := -1
+	outerExitIdx := -1
+	innerEnterIdx := -1
+	innerExitIdx := -1
+
+	for i, log := range logSequence {
+		switch log {
+		case "OuterOp-entering":
+			outerEnterIdx = i
+		case "OuterOp-exiting":
+			outerExitIdx = i
+		case "InnerOp-entering":
+			innerEnterIdx = i
+		case "InnerOp-exiting":
+			innerExitIdx = i
+		}
+	}
+
+	// Verify entry before exit for each operation
+	assert.Greater(t, outerExitIdx, outerEnterIdx, "OuterOp exit should come after OuterOp entry")
+	assert.Greater(t, innerExitIdx, innerEnterIdx, "InnerOp exit should come after InnerOp entry")
 }
 
 // TestLogEntryExitWithCallback tests custom log level and callback
@@ -172,76 +225,6 @@ func TestLogEntryExitDisabled(t *testing.T) {
 	assert.Empty(t, logOutput, "Should have no logs when logging is disabled")
 }
 
-// TestLogEntryExitF tests custom entry/exit callbacks
-func TestLogEntryExitF(t *testing.T) {
-	var entryCount, exitCount int
-
-	onEntry := func(ctx context.Context) IO[context.Context] {
-		return func() context.Context {
-			entryCount++
-			return ctx
-		}
-	}
-
-	onExit := func(res Result[string]) ReaderIO[any] {
-		return func(ctx context.Context) IO[any] {
-			return func() any {
-				exitCount++
-				return nil
-			}
-		}
-	}
-
-	operation := F.Pipe1(
-		Of("test"),
-		LogEntryExitF(onEntry, onExit),
-	)
-
-	res := operation(t.Context())()
-
-	assert.True(t, result.IsRight(res))
-	assert.Equal(t, 1, entryCount, "Entry callback should be called once")
-	assert.Equal(t, 1, exitCount, "Exit callback should be called once")
-}
-
-// TestLogEntryExitFWithError tests custom callbacks with error
-func TestLogEntryExitFWithError(t *testing.T) {
-	var entryCount, exitCount int
-	var capturedError error
-
-	onEntry := func(ctx context.Context) IO[context.Context] {
-		return func() context.Context {
-			entryCount++
-			return ctx
-		}
-	}
-
-	onExit := func(res Result[string]) ReaderIO[any] {
-		return func(ctx context.Context) IO[any] {
-			return func() any {
-				exitCount++
-				if result.IsLeft(res) {
-					_, capturedError = result.Unwrap(res)
-				}
-				return nil
-			}
-		}
-	}
-
-	testErr := errors.New("custom error")
-	operation := F.Pipe1(
-		Left[string](testErr),
-		LogEntryExitF(onEntry, onExit),
-	)
-
-	res := operation(t.Context())()
-
-	assert.True(t, result.IsLeft(res))
-	assert.Equal(t, 1, entryCount, "Entry callback should be called once")
-	assert.Equal(t, 1, exitCount, "Exit callback should be called once")
-	assert.Equal(t, testErr, capturedError, "Should capture the error")
-}
-
 // TestLoggingIDUniqueness tests that logging IDs are unique
 func TestLoggingIDUniqueness(t *testing.T) {
 	var buf bytes.Buffer
@@ -287,7 +270,8 @@ func TestLogEntryExitWithContextLogger(t *testing.T) {
 		Level: slog.LevelInfo,
 	}))
 
-	ctx := logging.WithLogger(contextLogger)(t.Context())
+	cancelFct, ctx := pair.Unpack(logging.WithLogger(contextLogger)(t.Context()))
+	defer cancelFct()
 
 	operation := F.Pipe1(
 		Of("context value"),
@@ -546,7 +530,8 @@ func TestTapSLogWithContextLogger(t *testing.T) {
 		Level: slog.LevelInfo,
 	}))
 
-	ctx := logging.WithLogger(contextLogger)(t.Context())
+	cancelFct, ctx := pair.Unpack(logging.WithLogger(contextLogger)(t.Context()))
+	defer cancelFct()
 
 	operation := F.Pipe2(
 		Of("test value"),
@@ -660,3 +645,138 @@ func TestSLogWithCallbackLogsError(t *testing.T) {
 	assert.Contains(t, logOutput, "warning error")
 	assert.Contains(t, logOutput, "level=WARN")
 }
+
+// TestTapSLogPreservesResult tests that TapSLog doesn't modify the result
+func TestTapSLogPreservesResult(t *testing.T) {
+	var buf bytes.Buffer
+	logger := slog.New(slog.NewTextHandler(&buf, &slog.HandlerOptions{
+		Level: slog.LevelInfo,
+	}))
+	oldLogger := logging.SetLogger(logger)
+	defer logging.SetLogger(oldLogger)
+
+	// Test with success value
+	successOp := F.Pipe2(
+		Of(42),
+		TapSLog[int]("Success value"),
+		Map(N.Mul(2)),
+	)
+
+	successRes := successOp(t.Context())()
+	assert.Equal(t, result.Of(84), successRes)
+
+	// Test with error value
+	testErr := errors.New("test error")
+	errorOp := F.Pipe2(
+		Left[int](testErr),
+		TapSLog[int]("Error value"),
+		Map(N.Mul(2)),
+	)
+
+	errorRes := errorOp(t.Context())()
+	assert.True(t, result.IsLeft(errorRes))
+
+	// Verify the error is preserved
+	_, err := result.Unwrap(errorRes)
+	assert.Equal(t, testErr, err)
+}
+
+// TestTapSLogChainBehavior tests that TapSLog properly chains with other operations
+func TestTapSLogChainBehavior(t *testing.T) {
+	var buf bytes.Buffer
+	logger := slog.New(slog.NewTextHandler(&buf, &slog.HandlerOptions{
+		Level: slog.LevelInfo,
+	}))
+	oldLogger := logging.SetLogger(logger)
+	defer logging.SetLogger(oldLogger)
+
+	// Create a pipeline with multiple TapSLog calls
+	step1 := F.Pipe2(
+		Of(1),
+		TapSLog[int]("Step 1"),
+		Map(N.Mul(2)),
+	)
+
+	step2 := F.Pipe2(
+		step1,
+		TapSLog[int]("Step 2"),
+		Map(N.Mul(3)),
+	)
+
+	pipeline := F.Pipe1(
+		step2,
+		TapSLog[int]("Step 3"),
+	)
+
+	res := pipeline(t.Context())()
+	assert.Equal(t, result.Of(6), res)
+
+	logOutput := buf.String()
+
+	// Verify all steps were logged
+	assert.Contains(t, logOutput, "Step 1")
+	assert.Contains(t, logOutput, "value=1")
+	assert.Contains(t, logOutput, "Step 2")
+	assert.Contains(t, logOutput, "value=2")
+	assert.Contains(t, logOutput, "Step 3")
+	assert.Contains(t, logOutput, "value=6")
+}
+
+// TestTapSLogWithNilValue tests TapSLog with nil pointer values
+func TestTapSLogWithNilValue(t *testing.T) {
+	var buf bytes.Buffer
+	logger := slog.New(slog.NewTextHandler(&buf, &slog.HandlerOptions{
+		Level: slog.LevelInfo,
+	}))
+	oldLogger := logging.SetLogger(logger)
+	defer logging.SetLogger(oldLogger)
+
+	type Data struct {
+		Value string
+	}
+
+	// Test with nil pointer
+	var nilData *Data
+	operation := F.Pipe1(
+		Of(nilData),
+		TapSLog[*Data]("Nil pointer value"),
+	)
+
+	res := operation(t.Context())()
+	assert.True(t, result.IsRight(res))
+
+	logOutput := buf.String()
+	assert.Contains(t, logOutput, "Nil pointer value")
+	// The exact representation of nil may vary, but it should be logged
+	assert.NotEmpty(t, logOutput)
+}
+
+// TestTapSLogLogsErrors verifies that TapSLog DOES log errors
+// TapSLog uses SLog internally, which logs both success values and errors
+func TestTapSLogLogsErrors(t *testing.T) {
+	var buf bytes.Buffer
+	logger := slog.New(slog.NewTextHandler(&buf, &slog.HandlerOptions{
+		Level: slog.LevelInfo,
+	}))
+	oldLogger := logging.SetLogger(logger)
+	defer logging.SetLogger(oldLogger)
+
+	testErr := errors.New("test error message")
+	pipeline := F.Pipe2(
+		Left[int](testErr),
+		TapSLog[int]("Error logging test"),
+		Map(N.Mul(2)),
+	)
+
+	res := pipeline(t.Context())()
+
+	// Verify the error is preserved
+	assert.True(t, result.IsLeft(res))
+
+	// Verify logging occurred for the error
+	logOutput := buf.String()
+	assert.NotEmpty(t, logOutput, "TapSLog should log when the Result is an error")
+	assert.Contains(t, logOutput, "Error logging test")
+	assert.Contains(t, logOutput, "error")
+	assert.Contains(t, logOutput, "test error message")
+}

v2/context/readerioresult/profunctor.go

@@ -78,6 +78,26 @@ func Contramap[A any](f pair.Kleisli[context.CancelFunc, context.Context, contex
 	return Local[A](f)
 }
 
+// ContramapIOK changes the context during the execution of a ReaderIOResult using an IO effect.
+// This is the contravariant functor operation with IO effects.
+//
+// ContramapIOK is an alias for LocalIOK and is useful for adapting a ReaderIOResult to work with
+// a modified context when the transformation itself requires side effects.
+//
+// Type Parameters:
+//   - A: The success type (unchanged)
+//
+// Parameters:
+//   - f: An IO Kleisli arrow that transforms the context with side effects
+//
+// Returns:
+//   - An Operator that takes a ReaderIOResult[A] and returns a ReaderIOResult[A]
+//
+// See Also:
+//   - Contramap: For pure context transformations
+//   - LocalIOK: The underlying implementation
+//
+//go:inline
 func ContramapIOK[A any](f io.Kleisli[context.Context, ContextCancel]) Operator[A, A] {
 	return LocalIOK[A](f)
 }
@@ -189,8 +209,6 @@ func LocalIOK[A any](f io.Kleisli[context.Context, ContextCancel]) Operator[A, A
 //
 //   - Local: For pure context transformations
 //   - LocalIOK: For context transformations with side effects that cannot fail
-//
-//go:inline
 func LocalIOResultK[A any](f ioresult.Kleisli[context.Context, ContextCancel]) Operator[A, A] {
 	return func(rr ReaderIOResult[A]) ReaderIOResult[A] {
 		return func(ctx context.Context) IOResult[A] {

v2/context/readerioresult/profunctor_test.go

@@ -77,6 +77,105 @@ func TestContramapBasic(t *testing.T) {
 	})
 }
 
+// TestContramapIOK tests ContramapIOK functionality
+func TestContramapIOK(t *testing.T) {
+	t.Run("transforms context with IO effect", func(t *testing.T) {
+		getValue := func(ctx context.Context) IOResult[string] {
+			return func() R.Result[string] {
+				if v := ctx.Value("requestID"); v != nil {
+					return R.Of(v.(string))
+				}
+				return R.Of("no-id")
+			}
+		}
+
+		addRequestID := func(ctx context.Context) io.IO[ContextCancel] {
+			return func() ContextCancel {
+				// Simulate generating a request ID via side effect
+				requestID := "req-12345"
+				newCtx := context.WithValue(ctx, "requestID", requestID)
+				return pair.MakePair(context.CancelFunc(func() {}), newCtx)
+			}
+		}
+
+		adapted := ContramapIOK[string](addRequestID)(getValue)
+		result := adapted(t.Context())()
+
+		assert.Equal(t, R.Of("req-12345"), result)
+	})
+
+	t.Run("preserves value type", func(t *testing.T) {
+		getValue := func(ctx context.Context) IOResult[int] {
+			return func() R.Result[int] {
+				if v := ctx.Value("counter"); v != nil {
+					return R.Of(v.(int))
+				}
+				return R.Of(0)
+			}
+		}
+
+		addCounter := func(ctx context.Context) io.IO[ContextCancel] {
+			return func() ContextCancel {
+				newCtx := context.WithValue(ctx, "counter", 999)
+				return pair.MakePair(context.CancelFunc(func() {}), newCtx)
+			}
+		}
+
+		adapted := ContramapIOK[int](addCounter)(getValue)
+		result := adapted(t.Context())()
+
+		assert.Equal(t, R.Of(999), result)
+	})
+
+	t.Run("calls cancel function", func(t *testing.T) {
+		cancelCalled := false
+
+		getValue := func(ctx context.Context) IOResult[string] {
+			return func() R.Result[string] {
+				return R.Of("test")
+			}
+		}
+
+		addData := func(ctx context.Context) io.IO[ContextCancel] {
+			return func() ContextCancel {
+				newCtx := context.WithValue(ctx, "data", "value")
+				cancelFunc := context.CancelFunc(func() {
+					cancelCalled = true
+				})
+				return pair.MakePair(cancelFunc, newCtx)
+			}
+		}
+
+		adapted := ContramapIOK[string](addData)(getValue)
+		_ = adapted(t.Context())()
+
+		assert.True(t, cancelCalled, "cancel function should be called")
+	})
+
+	t.Run("handles cancelled context", func(t *testing.T) {
+		getValue := func(ctx context.Context) IOResult[string] {
+			return func() R.Result[string] {
+				return R.Of("should not reach here")
+			}
+		}
+
+		addData := func(ctx context.Context) io.IO[ContextCancel] {
+			return func() ContextCancel {
+				newCtx := context.WithValue(ctx, "data", "value")
+				return pair.MakePair(context.CancelFunc(func() {}), newCtx)
+			}
+		}
+
+		ctx, cancel := context.WithCancel(t.Context())
+		cancel()
+
+		adapted := ContramapIOK[string](addData)(getValue)
+		result := adapted(ctx)()
+
+		assert.True(t, R.IsLeft(result))
+	})
+}
+
 // TestLocalBasic tests basic Local functionality
 func TestLocalBasic(t *testing.T) {
 	t.Run("adds value to context", func(t *testing.T) {

v2/context/readerreaderioresult/promap.go

@@ -102,6 +102,29 @@ func LocalIOResultK[A, R1, R2 any](f ioresult.Kleisli[R2, R1]) func(ReaderReader
 	return RRIOE.LocalIOEitherK[context.Context, A](f)
 }
 
+// LocalResultK transforms the outer environment of a ReaderReaderIOResult using a Result-based Kleisli arrow.
+// It allows you to modify the outer environment through a pure computation that can fail before
+// passing it to the ReaderReaderIOResult.
+//
+// This is useful when the outer environment transformation is a pure computation that can fail,
+// such as parsing, validation, or data transformation that doesn't require IO effects.
+//
+// The transformation happens in two stages:
+//  1. The Result function f is executed with the R2 environment to produce Result[R1]
+//  2. If successful (Ok), the R1 value is passed as the outer environment to the ReaderReaderIOResult[R1, A]
+//  3. If failed (Err), the error is propagated without executing the ReaderReaderIOResult
+//
+// Type Parameters:
+//   - A: The success type produced by the ReaderReaderIOResult
+//   - R1: The original outer environment type expected by the ReaderReaderIOResult
+//   - R2: The new input outer environment type
+//
+// Parameters:
+//   - f: A Result Kleisli arrow that transforms R2 to R1 with pure computation that can fail
+//
+// Returns:
+//   - A function that takes a ReaderReaderIOResult[R1, A] and returns a ReaderReaderIOResult[R2, A]
+//
 //go:inline
 func LocalResultK[A, R1, R2 any](f result.Kleisli[R2, R1]) func(ReaderReaderIOResult[R1, A]) ReaderReaderIOResult[R2, A] {
 	return RRIOE.LocalEitherK[context.Context, A](f)
@@ -162,6 +185,31 @@ func LocalReaderIOResultK[A, R1, R2 any](f readerioresult.Kleisli[R2, R1]) func(
 	return RRIOE.LocalReaderIOEitherK[A](f)
 }
 
+// LocalReaderReaderIOEitherK transforms the outer environment of a ReaderReaderIOResult using a ReaderReaderIOResult-based Kleisli arrow.
+// It allows you to modify the outer environment through a computation that depends on both the outer environment
+// and the inner context, and can perform IO effects that may fail.
+//
+// This is the most powerful Local variant, useful when the outer environment transformation requires:
+//   - Access to both the outer environment (R2) and inner context (context.Context)
+//   - IO operations that can fail
+//   - Complex transformations that need the full computational context
+//
+// The transformation happens in three stages:
+//  1. The ReaderReaderIOResult effect f is executed with the R2 outer environment and inner context
+//  2. If successful (Ok), the R1 value is passed as the outer environment to the ReaderReaderIOResult[R1, A]
+//  3. If failed (Err), the error is propagated without executing the ReaderReaderIOResult
+//
+// Type Parameters:
+//   - A: The success type produced by the ReaderReaderIOResult
+//   - R1: The original outer environment type expected by the ReaderReaderIOResult
+//   - R2: The new input outer environment type
+//
+// Parameters:
+//   - f: A ReaderReaderIOResult Kleisli arrow that transforms R2 to R1 with full context-aware IO effects that can fail
+//
+// Returns:
+//   - A function that takes a ReaderReaderIOResult[R1, A] and returns a ReaderReaderIOResult[R2, A]
+//
 //go:inline
 func LocalReaderReaderIOEitherK[A, R1, R2 any](f Kleisli[R2, R2, R1]) func(ReaderReaderIOResult[R1, A]) ReaderReaderIOResult[R2, A] {
 	return RRIOE.LocalReaderReaderIOEitherK[A](f)

v2/context/readerresult/logging_test.go

@@ -24,6 +24,7 @@ import (
 
 	"github.com/IBM/fp-go/v2/logging"
 	N "github.com/IBM/fp-go/v2/number"
+	"github.com/IBM/fp-go/v2/pair"
 	"github.com/IBM/fp-go/v2/result"
 	"github.com/stretchr/testify/assert"
 )
@@ -104,7 +105,8 @@ func TestSLogWithContextLogger(t *testing.T) {
 		Level: slog.LevelInfo,
 	}))
 
-	ctx := logging.WithLogger(contextLogger)(t.Context())
+	cancelFct, ctx := pair.Unpack(logging.WithLogger(contextLogger)(t.Context()))
+	defer cancelFct()
 
 	res1 := result.Of("test value")
 	logged := SLog[string]("Context logger test")(res1)(ctx)

v2/context/statereaderioresult/state.go

@@ -21,7 +21,7 @@ import (
 	RIORES "github.com/IBM/fp-go/v2/context/readerioresult"
 	"github.com/IBM/fp-go/v2/function"
 	"github.com/IBM/fp-go/v2/internal/statet"
-	RIOR "github.com/IBM/fp-go/v2/readerioresult"
+	"github.com/IBM/fp-go/v2/pair"
 	"github.com/IBM/fp-go/v2/result"
 )
 
@@ -202,21 +202,38 @@ func FromResult[S, A any](ma Result[A]) StateReaderIOResult[S, A] {
 // Combinators
 
 // Local runs a computation with a modified context.
-// The function f transforms the context before passing it to the computation.
+// The function f transforms the context before passing it to the computation,
+// returning both a new context and a CancelFunc that should be called to release resources.
+//
+// This is useful for:
+//   - Adding values to the context
+//   - Setting timeouts or deadlines
+//   - Modifying context metadata
+//
+// The CancelFunc is automatically called after the computation completes to ensure proper cleanup.
+//
+// Type Parameters:
+//   - S: The state type
+//   - A: The result type
+//
+// Parameters:
+//   - f: Function to transform the context, returning a new context and CancelFunc
+//
+// Returns:
+//   - A function that takes a StateReaderIOResult[S, A] and returns a StateReaderIOResult[S, A]
 //
 // Example:
 //
-//	// Modify context before running computation
-//	withTimeout := statereaderioresult.Local[AppState](
-//	    func(ctx context.Context) context.Context {
-//	        ctx, _ = context.WithTimeout(ctx, 60*time.Second)
-//	        return ctx
-//	    }
+//	// Add a timeout to a specific operation
+//	withTimeout := statereaderioresult.Local[AppState, Data](
+//	    func(ctx context.Context) (context.Context, context.CancelFunc) {
+//	        return context.WithTimeout(ctx, 60*time.Second)
+//	    },
 //	)
 //	result := withTimeout(computation)
-func Local[S, A any](f func(context.Context) context.Context) func(StateReaderIOResult[S, A]) StateReaderIOResult[S, A] {
+func Local[S, A any](f pair.Kleisli[context.CancelFunc, context.Context, context.Context]) Operator[S, A, A] {
 	return func(ma StateReaderIOResult[S, A]) StateReaderIOResult[S, A] {
-		return function.Flow2(ma, RIOR.Local[Pair[S, A]](f))
+		return function.Flow2(ma, RIORES.Local[Pair[S, A]](f))
 	}
 }
 

v2/context/statereaderioresult/statereaderioresult_test.go

@@ -25,6 +25,7 @@ import (
 	"github.com/IBM/fp-go/v2/io"
 	IOR "github.com/IBM/fp-go/v2/ioresult"
 	N "github.com/IBM/fp-go/v2/number"
+	"github.com/IBM/fp-go/v2/pair"
 	P "github.com/IBM/fp-go/v2/pair"
 	RES "github.com/IBM/fp-go/v2/result"
 	"github.com/stretchr/testify/assert"
@@ -264,8 +265,8 @@ func TestLocal(t *testing.T) {
 
 	// Modify context before running computation
 	result := Local[testState, string](
-		func(c context.Context) context.Context {
-			return context.WithValue(c, "key", "value2")
+		func(c context.Context) ContextCancel {
+			return pair.MakePair[context.CancelFunc](func() {}, context.WithValue(c, "key", "value2"))
 		},
 	)(comp)
 

v2/context/statereaderioresult/type.go

@@ -16,6 +16,8 @@
 package statereaderioresult
 
 import (
+	"context"
+
 	RIORES "github.com/IBM/fp-go/v2/context/readerioresult"
 	"github.com/IBM/fp-go/v2/endomorphism"
 	"github.com/IBM/fp-go/v2/io"
@@ -84,4 +86,11 @@ type (
 	Operator[S, A, B any] = Reader[StateReaderIOResult[S, A], StateReaderIOResult[S, B]]
 
 	Predicate[A any] = predicate.Predicate[A]
+
+	// ContextCancel represents a pair of a cancel function and a context.
+	// It is used in operations that create new contexts with cancellation capabilities.
+	//
+	// The first element is the CancelFunc that should be called to release resources.
+	// The second element is the new Context that was created.
+	ContextCancel = Pair[context.CancelFunc, context.Context]
 )

v2/logging/logger.go

@@ -23,6 +23,8 @@ import (
 	"log"
 	"log/slog"
 	"sync/atomic"
+
+	"github.com/IBM/fp-go/v2/pair"
 )
 
 // LoggingCallbacks creates a pair of logging callback functions from the provided loggers.
@@ -128,6 +130,7 @@ var loggerInContextKey loggerInContextType
 //	    logger.Info("Processing request")
 //	}
 func GetLoggerFromContext(ctx context.Context) *slog.Logger {
+	// using idomatic style to avoid import cycle
 	value, ok := ctx.Value(loggerInContextKey).(*slog.Logger)
 	if !ok {
 		return globalLogger.Load()
@@ -135,9 +138,11 @@ func GetLoggerFromContext(ctx context.Context) *slog.Logger {
 	return value
 }
 
-// WithLogger returns an endomorphism that adds a logger to a context.
-// An endomorphism is a function that takes a value and returns a value of the same type.
-// This function creates a context transformation that embeds the provided logger.
+func noop() {}
+
+// WithLogger returns a Kleisli arrow that adds a logger to a context.
+// A Kleisli arrow transforms a context into a ContextCancel pair containing
+// a no-op cancel function and the new context with the embedded logger.
 //
 // This is particularly useful in functional programming patterns where you want to
 // compose context transformations, or when working with middleware that needs to
@@ -147,7 +152,7 @@ func GetLoggerFromContext(ctx context.Context) *slog.Logger {
 //   - l: The *slog.Logger to embed in the context
 //
 // Returns:
-//   - An Endomorphism[context.Context] function that adds the logger to a context
+//   - A Kleisli arrow (function from context.Context to ContextCancel) that adds the logger to a context
 //
 // Example:
 //
@@ -156,13 +161,14 @@ func GetLoggerFromContext(ctx context.Context) *slog.Logger {
 //
 //	// Apply it to a context
 //	ctx := context.Background()
-//	ctxWithLogger := addLogger(ctx)
+//	result := addLogger(ctx)
+//	ctxWithLogger := pair.Second(result)
 //
 //	// Retrieve the logger later
 //	logger := GetLoggerFromContext(ctxWithLogger)
 //	logger.Info("Using context logger")
-func WithLogger(l *slog.Logger) Endomorphism[context.Context] {
-	return func(ctx context.Context) context.Context {
-		return context.WithValue(ctx, loggerInContextKey, l)
+func WithLogger(l *slog.Logger) pair.Kleisli[context.CancelFunc, context.Context, context.Context] {
+	return func(ctx context.Context) ContextCancel {
+		return pair.MakePair[context.CancelFunc](noop, context.WithValue(ctx, loggerInContextKey, l))
 	}
 }

v2/logging/logger_test.go

@@ -17,10 +17,13 @@ package logging
 
 import (
 	"bytes"
+	"context"
 	"log"
+	"log/slog"
 	"strings"
 	"testing"
 
+	"github.com/IBM/fp-go/v2/pair"
 	S "github.com/IBM/fp-go/v2/string"
 )
 
@@ -288,3 +291,355 @@ func BenchmarkLoggingCallbacks_Logging(b *testing.B) {
 		infoLog("benchmark message %d", i)
 	}
 }
+
+// TestSetLogger_Success tests setting a new global logger and verifying it returns the old one.
+func TestSetLogger_Success(t *testing.T) {
+	// Save original logger to restore later
+	originalLogger := GetLogger()
+	defer SetLogger(originalLogger)
+
+	// Create a new logger
+	var buf bytes.Buffer
+	handler := slog.NewTextHandler(&buf, nil)
+	newLogger := slog.New(handler)
+
+	// Set the new logger
+	oldLogger := SetLogger(newLogger)
+
+	// Verify old logger was returned
+	if oldLogger == nil {
+		t.Error("Expected SetLogger to return the previous logger")
+	}
+
+	// Verify new logger is now active
+	currentLogger := GetLogger()
+	if currentLogger != newLogger {
+		t.Error("Expected GetLogger to return the newly set logger")
+	}
+}
+
+// TestSetLogger_Multiple tests setting logger multiple times.
+func TestSetLogger_Multiple(t *testing.T) {
+	// Save original logger to restore later
+	originalLogger := GetLogger()
+	defer SetLogger(originalLogger)
+
+	// Create three loggers
+	logger1 := slog.New(slog.NewTextHandler(&bytes.Buffer{}, nil))
+	logger2 := slog.New(slog.NewTextHandler(&bytes.Buffer{}, nil))
+	logger3 := slog.New(slog.NewTextHandler(&bytes.Buffer{}, nil))
+
+	// Set first logger
+	old1 := SetLogger(logger1)
+	if GetLogger() != logger1 {
+		t.Error("Expected logger1 to be active")
+	}
+
+	// Set second logger
+	old2 := SetLogger(logger2)
+	if old2 != logger1 {
+		t.Error("Expected SetLogger to return logger1")
+	}
+	if GetLogger() != logger2 {
+		t.Error("Expected logger2 to be active")
+	}
+
+	// Set third logger
+	old3 := SetLogger(logger3)
+	if old3 != logger2 {
+		t.Error("Expected SetLogger to return logger2")
+	}
+	if GetLogger() != logger3 {
+		t.Error("Expected logger3 to be active")
+	}
+
+	// Restore to original
+	restored := SetLogger(old1)
+	if restored != logger3 {
+		t.Error("Expected SetLogger to return logger3")
+	}
+}
+
+// TestGetLogger_Default tests that GetLogger returns a valid logger by default.
+func TestGetLogger_Default(t *testing.T) {
+	logger := GetLogger()
+
+	if logger == nil {
+		t.Error("Expected GetLogger to return a non-nil logger")
+	}
+
+	// Verify it's usable
+	var buf bytes.Buffer
+	handler := slog.NewTextHandler(&buf, nil)
+	testLogger := slog.New(handler)
+
+	oldLogger := SetLogger(testLogger)
+	defer SetLogger(oldLogger)
+
+	GetLogger().Info("test message")
+	if !strings.Contains(buf.String(), "test message") {
+		t.Errorf("Expected logger to log message, got: %s", buf.String())
+	}
+}
+
+// TestGetLogger_AfterSet tests that GetLogger returns the logger set by SetLogger.
+func TestGetLogger_AfterSet(t *testing.T) {
+	originalLogger := GetLogger()
+	defer SetLogger(originalLogger)
+
+	var buf bytes.Buffer
+	handler := slog.NewTextHandler(&buf, nil)
+	customLogger := slog.New(handler)
+
+	SetLogger(customLogger)
+
+	retrievedLogger := GetLogger()
+	if retrievedLogger != customLogger {
+		t.Error("Expected GetLogger to return the custom logger")
+	}
+
+	// Verify it's the same instance by logging
+	retrievedLogger.Info("test")
+	if !strings.Contains(buf.String(), "test") {
+		t.Error("Expected retrieved logger to be the same instance")
+	}
+}
+
+// TestGetLoggerFromContext_WithLogger tests retrieving a logger from context.
+func TestGetLoggerFromContext_WithLogger(t *testing.T) {
+	var buf bytes.Buffer
+	handler := slog.NewTextHandler(&buf, nil)
+	contextLogger := slog.New(handler)
+
+	// Create context with logger using WithLogger
+	ctx := context.Background()
+	kleisli := WithLogger(contextLogger)
+	result := kleisli(ctx)
+	ctxWithLogger := pair.Second(result)
+
+	// Retrieve logger from context
+	retrievedLogger := GetLoggerFromContext(ctxWithLogger)
+
+	if retrievedLogger != contextLogger {
+		t.Error("Expected to retrieve the context logger")
+	}
+
+	// Verify it's the same instance by logging
+	retrievedLogger.Info("context test")
+	if !strings.Contains(buf.String(), "context test") {
+		t.Error("Expected retrieved logger to be the same instance")
+	}
+}
+
+// TestGetLoggerFromContext_WithoutLogger tests that it returns global logger when context has no logger.
+func TestGetLoggerFromContext_WithoutLogger(t *testing.T) {
+	originalLogger := GetLogger()
+	defer SetLogger(originalLogger)
+
+	var buf bytes.Buffer
+	handler := slog.NewTextHandler(&buf, nil)
+	globalLogger := slog.New(handler)
+	SetLogger(globalLogger)
+
+	// Create context without logger
+	ctx := context.Background()
+
+	// Should return global logger
+	retrievedLogger := GetLoggerFromContext(ctx)
+
+	if retrievedLogger != globalLogger {
+		t.Error("Expected to retrieve the global logger when context has no logger")
+	}
+
+	// Verify it's the same instance
+	retrievedLogger.Info("global test")
+	if !strings.Contains(buf.String(), "global test") {
+		t.Error("Expected retrieved logger to be the global logger")
+	}
+}
+
+// TestGetLoggerFromContext_NilContext tests behavior with nil context value.
+func TestGetLoggerFromContext_NilContext(t *testing.T) {
+	originalLogger := GetLogger()
+	defer SetLogger(originalLogger)
+
+	var buf bytes.Buffer
+	handler := slog.NewTextHandler(&buf, nil)
+	globalLogger := slog.New(handler)
+	SetLogger(globalLogger)
+
+	// Create context with wrong type value
+	ctx := context.WithValue(context.Background(), loggerInContextKey, "not a logger")
+
+	// Should return global logger when type assertion fails
+	retrievedLogger := GetLoggerFromContext(ctx)
+
+	if retrievedLogger != globalLogger {
+		t.Error("Expected to retrieve the global logger when context value is wrong type")
+	}
+}
+
+// TestWithLogger_CreatesContextWithLogger tests that WithLogger adds logger to context.
+func TestWithLogger_CreatesContextWithLogger(t *testing.T) {
+	var buf bytes.Buffer
+	handler := slog.NewTextHandler(&buf, nil)
+	testLogger := slog.New(handler)
+
+	// Create Kleisli arrow
+	kleisli := WithLogger(testLogger)
+
+	// Apply to context
+	ctx := context.Background()
+	result := kleisli(ctx)
+
+	// Verify result is a ContextCancel pair
+	cancelFunc := pair.First(result)
+	newCtx := pair.Second(result)
+
+	if cancelFunc == nil {
+		t.Error("Expected cancel function to be non-nil")
+	}
+
+	if newCtx == nil {
+		t.Error("Expected new context to be non-nil")
+	}
+
+	// Verify logger is in context
+	retrievedLogger := GetLoggerFromContext(newCtx)
+	if retrievedLogger != testLogger {
+		t.Error("Expected logger to be in the new context")
+	}
+}
+
+// TestWithLogger_CancelFuncIsNoop tests that the cancel function is a no-op.
+func TestWithLogger_CancelFuncIsNoop(t *testing.T) {
+	testLogger := slog.New(slog.NewTextHandler(&bytes.Buffer{}, nil))
+	kleisli := WithLogger(testLogger)
+
+	ctx := context.Background()
+	result := kleisli(ctx)
+	cancelFunc := pair.First(result)
+
+	// Calling cancel should not panic
+	defer func() {
+		if r := recover(); r != nil {
+			t.Errorf("Cancel function panicked: %v", r)
+		}
+	}()
+
+	cancelFunc()
+}
+
+// TestWithLogger_PreservesOriginalContext tests that original context is not modified.
+func TestWithLogger_PreservesOriginalContext(t *testing.T) {
+	originalLogger := GetLogger()
+	defer SetLogger(originalLogger)
+
+	var buf bytes.Buffer
+	handler := slog.NewTextHandler(&buf, nil)
+	globalLogger := slog.New(handler)
+	SetLogger(globalLogger)
+
+	testLogger := slog.New(slog.NewTextHandler(&bytes.Buffer{}, nil))
+	kleisli := WithLogger(testLogger)
+
+	// Original context without logger
+	originalCtx := context.Background()
+
+	// Apply transformation
+	result := kleisli(originalCtx)
+	newCtx := pair.Second(result)
+
+	// Original context should still return global logger
+	originalCtxLogger := GetLoggerFromContext(originalCtx)
+	if originalCtxLogger != globalLogger {
+		t.Error("Expected original context to still use global logger")
+	}
+
+	// New context should have the test logger
+	newCtxLogger := GetLoggerFromContext(newCtx)
+	if newCtxLogger != testLogger {
+		t.Error("Expected new context to have the test logger")
+	}
+}
+
+// TestWithLogger_Composition tests composing multiple WithLogger calls.
+func TestWithLogger_Composition(t *testing.T) {
+	logger1 := slog.New(slog.NewTextHandler(&bytes.Buffer{}, nil))
+	logger2 := slog.New(slog.NewTextHandler(&bytes.Buffer{}, nil))
+
+	kleisli1 := WithLogger(logger1)
+	kleisli2 := WithLogger(logger2)
+
+	ctx := context.Background()
+
+	// Apply first transformation
+	result1 := kleisli1(ctx)
+	ctx1 := pair.Second(result1)
+
+	// Verify first logger
+	if GetLoggerFromContext(ctx1) != logger1 {
+		t.Error("Expected first logger in context after first transformation")
+	}
+
+	// Apply second transformation (should override)
+	result2 := kleisli2(ctx1)
+	ctx2 := pair.Second(result2)
+
+	// Verify second logger (should override first)
+	if GetLoggerFromContext(ctx2) != logger2 {
+		t.Error("Expected second logger to override first logger")
+	}
+}
+
+// BenchmarkSetLogger benchmarks setting the global logger.
+func BenchmarkSetLogger(b *testing.B) {
+	logger := slog.New(slog.NewTextHandler(&bytes.Buffer{}, nil))
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		SetLogger(logger)
+	}
+}
+
+// BenchmarkGetLogger benchmarks getting the global logger.
+func BenchmarkGetLogger(b *testing.B) {
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		GetLogger()
+	}
+}
+
+// BenchmarkGetLoggerFromContext_WithLogger benchmarks retrieving logger from context.
+func BenchmarkGetLoggerFromContext_WithLogger(b *testing.B) {
+	logger := slog.New(slog.NewTextHandler(&bytes.Buffer{}, nil))
+	kleisli := WithLogger(logger)
+	ctx := pair.Second(kleisli(context.Background()))
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		GetLoggerFromContext(ctx)
+	}
+}
+
+// BenchmarkGetLoggerFromContext_WithoutLogger benchmarks retrieving global logger from context.
+func BenchmarkGetLoggerFromContext_WithoutLogger(b *testing.B) {
+	ctx := context.Background()
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		GetLoggerFromContext(ctx)
+	}
+}
+
+// BenchmarkWithLogger benchmarks creating context with logger.
+func BenchmarkWithLogger(b *testing.B) {
+	logger := slog.New(slog.NewTextHandler(&bytes.Buffer{}, nil))
+	kleisli := WithLogger(logger)
+	ctx := context.Background()
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		kleisli(ctx)
+	}
+}

v2/logging/types.go

@@ -16,7 +16,10 @@
 package logging
 
 import (
+	"context"
+
 	"github.com/IBM/fp-go/v2/endomorphism"
+	"github.com/IBM/fp-go/v2/pair"
 )
 
 type (
@@ -39,4 +42,15 @@ type (
 	//	ctx := context.Background()
 	//	newCtx := addLogger(ctx) // Both ctx and newCtx are context.Context
 	Endomorphism[A any] = endomorphism.Endomorphism[A]
+
+	// Pair represents a tuple of two values of types A and B.
+	// It is used to group two related values together.
+	Pair[A, B any] = pair.Pair[A, B]
+
+	// ContextCancel represents a pair of a cancel function and a context.
+	// It is used in operations that create new contexts with cancellation capabilities.
+	//
+	// The first element is the CancelFunc that should be called to release resources.
+	// The second element is the new Context that was created.
+	ContextCancel = Pair[context.CancelFunc, context.Context]
 )

v2/optics/codec/bind.go

@@ -26,6 +26,83 @@ import (
 	"github.com/IBM/fp-go/v2/semigroup"
 )
 
+// Do creates the initial empty codec to be used as the starting point for
+// do-notation style codec construction.
+//
+// This is the entry point for building up a struct codec field-by-field using
+// the applicative and monadic sequencing operators ApSL, ApSO, and Bind.
+// It wraps Empty and lifts a lazily-evaluated default Pair[O, A] into a
+// Type[A, O, I] that ignores its input and always succeeds with the default value.
+//
+// # Type Parameters
+//
+//   - I: The input type for decoding (what the codec reads from)
+//   - A: The target struct type being built up (what the codec decodes to)
+//   - O: The output type for encoding (what the codec writes to)
+//
+// # Parameters
+//
+//   - e: A Lazy[Pair[O, A]] providing the initial default values:
+//   - pair.Head(e()): The default encoded output O (e.g. an empty monoid value)
+//   - pair.Tail(e()): The initial zero value of the struct A (e.g. MyStruct{})
+//
+// # Returns
+//
+//   - A Type[A, O, I] that always decodes to the default A and encodes to the
+//     default O, regardless of input. This is then transformed by chaining
+//     ApSL, ApSO, or Bind operators to add fields one by one.
+//
+// # Example Usage
+//
+// Building a struct codec using do-notation style:
+//
+//	import (
+//	    "github.com/IBM/fp-go/v2/function"
+//	    "github.com/IBM/fp-go/v2/lazy"
+//	    "github.com/IBM/fp-go/v2/optics/codec"
+//	    "github.com/IBM/fp-go/v2/optics/lens"
+//	    "github.com/IBM/fp-go/v2/pair"
+//	    S "github.com/IBM/fp-go/v2/string"
+//	)
+//
+//	type Person struct {
+//	    Name string
+//	    Age  int
+//	}
+//
+//	nameLens := lens.MakeLens(
+//	    func(p Person) string { return p.Name },
+//	    func(p Person, name string) Person { p.Name = name; return p },
+//	)
+//	ageLens := lens.MakeLens(
+//	    func(p Person) int { return p.Age },
+//	    func(p Person, age int) Person { p.Age = age; return p },
+//	)
+//
+//	personCodec := F.Pipe2(
+//	    codec.Do[any, Person, string](lazy.Of(pair.MakePair("", Person{}))),
+//	    codec.ApSL(S.Monoid, nameLens, codec.String()),
+//	    codec.ApSL(S.Monoid, ageLens, codec.Int()),
+//	)
+//
+// # Notes
+//
+//   - Do is typically the first call in a codec pipeline, followed by ApSL, ApSO, or Bind
+//   - The lazy pair should use the monoid's empty value for O and the zero value for A
+//   - For convenience, use Struct to create the initial codec for named struct types
+//
+// # See Also
+//
+//   - Empty: The underlying codec constructor that Do delegates to
+//   - ApSL: Applicative sequencing for required struct fields via Lens
+//   - ApSO: Applicative sequencing for optional struct fields via Optional
+//   - Bind: Monadic sequencing for context-dependent field codecs
+//
+//go:inline
+func Do[I, A, O any](e Lazy[Pair[O, A]]) Type[A, O, I] {
+	return Empty[I](e)
+}
+
 // ApSL creates an applicative sequencing operator for codecs using a lens.
 //
 // This function implements the "ApS" (Applicative Sequencing) pattern for codecs,
@@ -297,3 +374,132 @@ func ApSO[S, T, O, I any](
 		)
 	}
 }
+
+// Bind creates a monadic sequencing operator for codecs using a lens and a Kleisli arrow.
+//
+// This function implements the "Bind" (monadic bind / chain) pattern for codecs,
+// allowing you to build up complex codecs where the codec for a field depends on
+// the current decoded value of the struct. Unlike ApSL which uses a fixed field
+// codec, Bind accepts a Kleisli arrow — a function from the current struct value S
+// to a Type[T, O, I] — enabling context-sensitive codec construction.
+//
+// The function combines:
+//   - Encoding: Evaluates the Kleisli arrow f on the current struct value s to obtain
+//     the field codec, extracts the field T using the lens, encodes it with that codec,
+//     and combines it with the base encoding using the monoid.
+//   - Validation: Validates the base struct first (monadic sequencing), then uses the
+//     Kleisli arrow to obtain the field codec for the decoded struct value, and validates
+//     the field through the lens. Errors are propagated but NOT accumulated (fail-fast
+//     semantics, unlike ApSL which accumulates errors).
+//
+// # Type Parameters
+//
+//   - S: The source struct type (what we're building a codec for)
+//   - T: The field type accessed by the lens
+//   - O: The output type for encoding (must have a monoid)
+//   - I: The input type for decoding
+//
+// # Parameters
+//
+//   - m: A Monoid[O] for combining encoded outputs
+//   - l: A Lens[S, T] that focuses on a specific field in S
+//   - f: A Kleisli[S, T, O, I] — a function from S to Type[T, O, I] — that produces
+//     the field codec based on the current struct value
+//
+// # Returns
+//
+// An Operator[S, S, O, I] that transforms a base codec by adding the field
+// specified by the lens, where the field codec is determined by the Kleisli arrow.
+//
+// # How It Works
+//
+// 1. **Encoding**: When encoding a value of type S:
+//   - Evaluate f(s) to obtain the field codec fa
+//   - Extract the field T using l.Get
+//   - Encode T to O using fa.Encode
+//   - Combine with the base encoding using the monoid
+//
+// 2. **Validation**: When validating input I:
+//   - Run the base validation to obtain a decoded S (fail-fast: stop on base failure)
+//   - For the decoded S, evaluate f(s) to obtain the field codec fa
+//   - Validate the input I using fa.Validate
+//   - Set the validated T into S using l.Set
+//
+// 3. **Type Checking**: Preserves the base type checker
+//
+// # Difference from ApSL
+//
+// Unlike ApSL which uses a fixed field codec:
+//   - ApSL: Field codec is fixed at construction time; errors are accumulated
+//   - Bind: Field codec depends on the current struct value (Kleisli arrow); validation
+//     uses monadic sequencing (fail-fast on base failure)
+//   - Bind is more powerful but less parallel than ApSL
+//
+// # Example
+//
+//	import (
+//	    "github.com/IBM/fp-go/v2/optics/codec"
+//	    "github.com/IBM/fp-go/v2/optics/lens"
+//	    S "github.com/IBM/fp-go/v2/string"
+//	)
+//
+//	type Config struct {
+//	    Mode  string
+//	    Value int
+//	}
+//
+//	modeLens := lens.MakeLens(
+//	    func(c Config) string { return c.Mode },
+//	    func(c Config, mode string) Config { c.Mode = mode; return c },
+//	)
+//
+//	// Build a Config codec where the Value codec depends on the Mode
+//	configCodec := F.Pipe1(
+//	    codec.Struct[Config]("Config"),
+//	    codec.Bind(S.Monoid, modeLens, func(c Config) codec.Type[string, string, any] {
+//	        return codec.String()
+//	    }),
+//	)
+//
+// # Use Cases
+//
+//   - Building codecs where a field's codec depends on another field's value
+//   - Implementing discriminated unions or tagged variants
+//   - Context-sensitive validation (e.g., validate field B differently based on field A)
+//   - Dependent type-like patterns in codec construction
+//
+// # Notes
+//
+//   - The monoid determines how encoded outputs are combined
+//   - The lens must be total (handle all cases safely)
+//   - Validation uses monadic (fail-fast) sequencing: if the base codec fails,
+//     the Kleisli arrow is never evaluated
+//   - The name is automatically generated for debugging purposes
+//
+// See also:
+//   - ApSL: Applicative sequencing with a fixed lens codec (error accumulation)
+//   - Kleisli: The function type from S to Type[T, O, I]
+//   - validate.Bind: The underlying validate-level bind combinator
+func Bind[S, T, O, I any](
+	m Monoid[O],
+	l Lens[S, T],
+	f Kleisli[S, T, O, I],
+) Operator[S, S, O, I] {
+	name := fmt.Sprintf("Bind[%s]", l)
+	val := F.Curry2(Type[T, O, I].Validate)
+
+	return func(t Type[S, O, I]) Type[S, O, I] {
+
+		return MakeType(
+			name,
+			t.Is,
+			F.Pipe1(
+				t.Validate,
+				validate.Bind(l.Set, F.Flow2(f, val)),
+			),
+			func(s S) O {
+				return m.Concat(t.Encode(s), f(s).Encode(l.Get(s)))
+			},
+		)
+	}
+}

v2/optics/codec/bind_test.go

@@ -814,3 +814,588 @@ func TestApSO_ErrorAccumulation(t *testing.T) {
 		assert.NotEmpty(t, errors, "Should have validation errors")
 	})
 }
+
+// TestBind_EncodingCombination verifies that Bind combines the base encoding with
+// the field encoding produced by the Kleisli arrow using the monoid.
+func TestBind_EncodingCombination(t *testing.T) {
+	t.Run("combines base and field encodings using monoid", func(t *testing.T) {
+		// Lens for Person.Name
+		nameLens := lens.MakeLens(
+			func(p Person) string { return p.Name },
+			func(p Person, name string) Person {
+				return Person{Name: name, Age: p.Age}
+			},
+		)
+
+		// Base codec encodes to "Person:"
+		baseCodec := MakeType(
+			"Person",
+			func(i any) validation.Result[Person] {
+				if p, ok := i.(Person); ok {
+					return validation.ToResult(validation.Success(p))
+				}
+				return validation.ToResult(validation.Failures[Person](validation.Errors{
+					&validation.ValidationError{Value: i, Messsage: "expected Person"},
+				}))
+			},
+			func(i any) Decode[Context, Person] {
+				return func(ctx Context) validation.Validation[Person] {
+					if p, ok := i.(Person); ok {
+						return validation.Success(p)
+					}
+					return validation.FailureWithMessage[Person](i, "expected Person")(ctx)
+				}
+			},
+			func(p Person) string { return "Person:" },
+		)
+
+		// Kleisli arrow: always returns a string identity codec regardless of struct value
+		kleisli := func(p Person) Type[string, string, any] {
+			return MakeType(
+				"Name",
+				func(i any) validation.Result[string] {
+					if s, ok := i.(string); ok {
+						return validation.ToResult(validation.Success(s))
+					}
+					return validation.ToResult(validation.Failures[string](validation.Errors{
+						&validation.ValidationError{Value: i, Messsage: "expected string"},
+					}))
+				},
+				func(i any) Decode[Context, string] {
+					return func(ctx Context) validation.Validation[string] {
+						if s, ok := i.(string); ok {
+							return validation.Success(s)
+						}
+						return validation.FailureWithMessage[string](i, "expected string")(ctx)
+					}
+				},
+				F.Identity[string],
+			)
+		}
+
+		operator := Bind(S.Monoid, nameLens, kleisli)
+		enhancedCodec := operator(baseCodec)
+
+		person := Person{Name: "Alice", Age: 30}
+		encoded := enhancedCodec.Encode(person)
+
+		// Encoding should include both the base prefix and the field value
+		assert.Contains(t, encoded, "Person:")
+		assert.Contains(t, encoded, "Alice")
+	})
+}
+
+// TestBind_KleisliArrowReceivesCurrentValue verifies that the Kleisli arrow f
+// receives the current struct value when producing the field codec.
+func TestBind_KleisliArrowReceivesCurrentValue(t *testing.T) {
+	t.Run("kleisli arrow receives current struct value during encoding", func(t *testing.T) {
+		nameLens := lens.MakeLens(
+			func(p Person) string { return p.Name },
+			func(p Person, name string) Person {
+				return Person{Name: name, Age: p.Age}
+			},
+		)
+
+		baseCodec := MakeType(
+			"Person",
+			func(i any) validation.Result[Person] {
+				if p, ok := i.(Person); ok {
+					return validation.ToResult(validation.Success(p))
+				}
+				return validation.ToResult(validation.Failures[Person](validation.Errors{
+					&validation.ValidationError{Value: i, Messsage: "expected Person"},
+				}))
+			},
+			func(i any) Decode[Context, Person] {
+				return func(ctx Context) validation.Validation[Person] {
+					if p, ok := i.(Person); ok {
+						return validation.Success(p)
+					}
+					return validation.FailureWithMessage[Person](i, "expected Person")(ctx)
+				}
+			},
+			func(p Person) string { return "" },
+		)
+
+		// Kleisli arrow that uses the struct value to produce a prefix in the encoding
+		var capturedPerson Person
+		kleisli := func(p Person) Type[string, string, any] {
+			capturedPerson = p
+			return MakeType(
+				"Name",
+				func(i any) validation.Result[string] {
+					if s, ok := i.(string); ok {
+						return validation.ToResult(validation.Success(s))
+					}
+					return validation.ToResult(validation.Failures[string](validation.Errors{
+						&validation.ValidationError{Value: i, Messsage: "expected string"},
+					}))
+				},
+				func(i any) Decode[Context, string] {
+					return func(ctx Context) validation.Validation[string] {
+						if s, ok := i.(string); ok {
+							return validation.Success(s)
+						}
+						return validation.FailureWithMessage[string](i, "expected string")(ctx)
+					}
+				},
+				F.Identity[string],
+			)
+		}
+
+		operator := Bind(S.Monoid, nameLens, kleisli)
+		enhancedCodec := operator(baseCodec)
+
+		person := Person{Name: "Bob", Age: 25}
+		enhancedCodec.Encode(person)
+
+		// The Kleisli arrow should have been called with the actual struct value
+		assert.Equal(t, person, capturedPerson)
+	})
+}
+
+// TestBind_ValidationSuccess verifies that Bind correctly validates and decodes
+// a struct when both the base and field validations succeed.
+func TestBind_ValidationSuccess(t *testing.T) {
+	t.Run("succeeds when base and field validations pass", func(t *testing.T) {
+		nameLens := lens.MakeLens(
+			func(p Person) string { return p.Name },
+			func(p Person, name string) Person {
+				return Person{Name: name, Age: p.Age}
+			},
+		)
+
+		baseCodec := MakeType(
+			"Person",
+			func(i any) validation.Result[Person] {
+				if p, ok := i.(Person); ok {
+					return validation.ToResult(validation.Success(p))
+				}
+				return validation.ToResult(validation.Failures[Person](validation.Errors{
+					&validation.ValidationError{Value: i, Messsage: "expected Person"},
+				}))
+			},
+			func(i any) Decode[Context, Person] {
+				return func(ctx Context) validation.Validation[Person] {
+					if p, ok := i.(Person); ok {
+						return validation.Success(p)
+					}
+					return validation.FailureWithMessage[Person](i, "expected Person")(ctx)
+				}
+			},
+			func(p Person) string { return "" },
+		)
+
+		// The field codec receives the same input I (any = Person struct).
+		// It must extract the Name field from the Person input.
+		kleisli := func(p Person) Type[string, string, any] {
+			return MakeType(
+				"Name",
+				func(i any) validation.Result[string] {
+					if person, ok := i.(Person); ok {
+						return validation.ToResult(validation.Success(person.Name))
+					}
+					return validation.ToResult(validation.Failures[string](validation.Errors{
+						&validation.ValidationError{Value: i, Messsage: "expected Person"},
+					}))
+				},
+				func(i any) Decode[Context, string] {
+					return func(ctx Context) validation.Validation[string] {
+						if person, ok := i.(Person); ok {
+							return validation.Success(person.Name)
+						}
+						return validation.FailureWithMessage[string](i, "expected Person")(ctx)
+					}
+				},
+				F.Identity[string],
+			)
+		}
+
+		operator := Bind(S.Monoid, nameLens, kleisli)
+		enhancedCodec := operator(baseCodec)
+
+		person := Person{Name: "Carol", Age: 28}
+		result := enhancedCodec.Decode(person)
+
+		assert.True(t, either.IsRight(result), "Should succeed when both validations pass")
+	})
+}
+
+// TestBind_ValidationFailsOnBaseFailure verifies that Bind uses fail-fast (monadic)
+// semantics: if the base codec fails, the Kleisli arrow is never evaluated.
+func TestBind_ValidationFailsOnBaseFailure(t *testing.T) {
+	t.Run("fails fast when base validation fails", func(t *testing.T) {
+		nameLens := lens.MakeLens(
+			func(p Person) string { return p.Name },
+			func(p Person, name string) Person {
+				return Person{Name: name, Age: p.Age}
+			},
+		)
+
+		// Base codec always fails
+		baseCodec := MakeType(
+			"Person",
+			func(i any) validation.Result[Person] {
+				return validation.ToResult(validation.Failures[Person](validation.Errors{
+					&validation.ValidationError{Value: i, Messsage: "base always fails"},
+				}))
+			},
+			func(i any) Decode[Context, Person] {
+				return func(ctx Context) validation.Validation[Person] {
+					return validation.FailureWithMessage[Person](i, "base always fails")(ctx)
+				}
+			},
+			func(p Person) string { return "" },
+		)
+
+		kleisliCalled := false
+		kleisli := func(p Person) Type[string, string, any] {
+			kleisliCalled = true
+			return MakeType(
+				"Name",
+				func(i any) validation.Result[string] {
+					if s, ok := i.(string); ok {
+						return validation.ToResult(validation.Success(s))
+					}
+					return validation.ToResult(validation.Failures[string](validation.Errors{
+						&validation.ValidationError{Value: i, Messsage: "expected string"},
+					}))
+				},
+				func(i any) Decode[Context, string] {
+					return func(ctx Context) validation.Validation[string] {
+						if s, ok := i.(string); ok {
+							return validation.Success(s)
+						}
+						return validation.FailureWithMessage[string](i, "expected string")(ctx)
+					}
+				},
+				F.Identity[string],
+			)
+		}
+
+		operator := Bind(S.Monoid, nameLens, kleisli)
+		enhancedCodec := operator(baseCodec)
+
+		person := Person{Name: "Dave", Age: 40}
+		result := enhancedCodec.Decode(person)
+
+		assert.True(t, either.IsLeft(result), "Should fail when base validation fails")
+		assert.False(t, kleisliCalled, "Kleisli arrow should NOT be called when base fails")
+	})
+}
+
+// TestBind_ValidationFailsOnFieldFailure verifies that Bind propagates field
+// validation errors when the Kleisli arrow's codec fails.
+func TestBind_ValidationFailsOnFieldFailure(t *testing.T) {
+	t.Run("fails when field validation from kleisli codec fails", func(t *testing.T) {
+		nameLens := lens.MakeLens(
+			func(p Person) string { return p.Name },
+			func(p Person, name string) Person {
+				return Person{Name: name, Age: p.Age}
+			},
+		)
+
+		// Base codec succeeds
+		baseCodec := MakeType(
+			"Person",
+			func(i any) validation.Result[Person] {
+				if p, ok := i.(Person); ok {
+					return validation.ToResult(validation.Success(p))
+				}
+				return validation.ToResult(validation.Failures[Person](validation.Errors{
+					&validation.ValidationError{Value: i, Messsage: "expected Person"},
+				}))
+			},
+			func(i any) Decode[Context, Person] {
+				return func(ctx Context) validation.Validation[Person] {
+					if p, ok := i.(Person); ok {
+						return validation.Success(p)
+					}
+					return validation.FailureWithMessage[Person](i, "expected Person")(ctx)
+				}
+			},
+			func(p Person) string { return "" },
+		)
+
+		// Kleisli arrow returns a codec that always fails regardless of input
+		kleisli := func(p Person) Type[string, string, any] {
+			return MakeType(
+				"Name",
+				func(i any) validation.Result[string] {
+					return validation.ToResult(validation.Failures[string](validation.Errors{
+						&validation.ValidationError{Value: i, Messsage: "field always fails"},
+					}))
+				},
+				func(i any) Decode[Context, string] {
+					return func(ctx Context) validation.Validation[string] {
+						return validation.FailureWithMessage[string](i, "field always fails")(ctx)
+					}
+				},
+				F.Identity[string],
+			)
+		}
+
+		operator := Bind(S.Monoid, nameLens, kleisli)
+		enhancedCodec := operator(baseCodec)
+
+		// The field codec receives the same input (Person) and always fails
+		person := Person{Name: "Eve", Age: 22}
+		result := enhancedCodec.Decode(person)
+
+		assert.True(t, either.IsLeft(result), "Should fail when field validation fails")
+
+		errors := either.MonadFold(result,
+			F.Identity[validation.Errors],
+			func(Person) validation.Errors { return nil },
+		)
+		assert.NotEmpty(t, errors, "Should have validation errors from field codec")
+	})
+}
+
+// TestBind_TypeCheckingPreserved verifies that Bind preserves the base type checker.
+func TestBind_TypeCheckingPreserved(t *testing.T) {
+	t.Run("preserves base type checker", func(t *testing.T) {
+		nameLens := lens.MakeLens(
+			func(p Person) string { return p.Name },
+			func(p Person, name string) Person {
+				return Person{Name: name, Age: p.Age}
+			},
+		)
+
+		baseCodec := MakeType(
+			"Person",
+			func(i any) validation.Result[Person] {
+				if p, ok := i.(Person); ok {
+					return validation.ToResult(validation.Success(p))
+				}
+				return validation.ToResult(validation.Failures[Person](validation.Errors{
+					&validation.ValidationError{Value: i, Messsage: "expected Person"},
+				}))
+			},
+			func(i any) Decode[Context, Person] {
+				return func(ctx Context) validation.Validation[Person] {
+					if p, ok := i.(Person); ok {
+						return validation.Success(p)
+					}
+					return validation.FailureWithMessage[Person](i, "expected Person")(ctx)
+				}
+			},
+			func(p Person) string { return "" },
+		)
+
+		kleisli := func(p Person) Type[string, string, any] {
+			return MakeType(
+				"Name",
+				func(i any) validation.Result[string] {
+					if s, ok := i.(string); ok {
+						return validation.ToResult(validation.Success(s))
+					}
+					return validation.ToResult(validation.Failures[string](validation.Errors{
+						&validation.ValidationError{Value: i, Messsage: "expected string"},
+					}))
+				},
+				func(i any) Decode[Context, string] {
+					return func(ctx Context) validation.Validation[string] {
+						if s, ok := i.(string); ok {
+							return validation.Success(s)
+						}
+						return validation.FailureWithMessage[string](i, "expected string")(ctx)
+					}
+				},
+				F.Identity[string],
+			)
+		}
+
+		operator := Bind(S.Monoid, nameLens, kleisli)
+		enhancedCodec := operator(baseCodec)
+
+		// Valid type
+		person := Person{Name: "Frank", Age: 35}
+		isResult := enhancedCodec.Is(person)
+		assert.True(t, either.IsRight(isResult), "Should accept Person type")
+
+		// Invalid type
+		invalidResult := enhancedCodec.Is("not a person")
+		assert.True(t, either.IsLeft(invalidResult), "Should reject non-Person type")
+	})
+}
+
+// TestBind_Naming verifies that Bind generates a descriptive name for the codec.
+func TestBind_Naming(t *testing.T) {
+	t.Run("generates descriptive name containing Bind and lens info", func(t *testing.T) {
+		nameLens := lens.MakeLens(
+			func(p Person) string { return p.Name },
+			func(p Person, name string) Person {
+				return Person{Name: name, Age: p.Age}
+			},
+		)
+
+		baseCodec := MakeType(
+			"Person",
+			func(i any) validation.Result[Person] {
+				if p, ok := i.(Person); ok {
+					return validation.ToResult(validation.Success(p))
+				}
+				return validation.ToResult(validation.Failures[Person](validation.Errors{
+					&validation.ValidationError{Value: i, Messsage: "expected Person"},
+				}))
+			},
+			func(i any) Decode[Context, Person] {
+				return func(ctx Context) validation.Validation[Person] {
+					if p, ok := i.(Person); ok {
+						return validation.Success(p)
+					}
+					return validation.FailureWithMessage[Person](i, "expected Person")(ctx)
+				}
+			},
+			func(p Person) string { return "" },
+		)
+
+		kleisli := func(p Person) Type[string, string, any] {
+			return MakeType(
+				"Name",
+				func(i any) validation.Result[string] {
+					if s, ok := i.(string); ok {
+						return validation.ToResult(validation.Success(s))
+					}
+					return validation.ToResult(validation.Failures[string](validation.Errors{
+						&validation.ValidationError{Value: i, Messsage: "expected string"},
+					}))
+				},
+				func(i any) Decode[Context, string] {
+					return func(ctx Context) validation.Validation[string] {
+						if s, ok := i.(string); ok {
+							return validation.Success(s)
+						}
+						return validation.FailureWithMessage[string](i, "expected string")(ctx)
+					}
+				},
+				F.Identity[string],
+			)
+		}
+
+		operator := Bind(S.Monoid, nameLens, kleisli)
+		enhancedCodec := operator(baseCodec)
+
+		name := enhancedCodec.Name()
+		assert.Contains(t, name, "Bind", "Name should contain 'Bind'")
+	})
+}
+
+// TestBind_DependentFieldCodec verifies that the Kleisli arrow can produce
+// different codecs based on the current struct value (the key differentiator
+// from ApSL).
+//
+// The field codec Type[T, O, I] receives the same input I as the base codec.
+// It must extract the field value from that input. The Kleisli arrow f(s)
+// produces a different codec depending on the already-decoded struct value s.
+func TestBind_DependentFieldCodec(t *testing.T) {
+	t.Run("kleisli arrow produces different codecs based on struct value", func(t *testing.T) {
+		// Lens for Person.Name
+		nameLens := lens.MakeLens(
+			func(p Person) string { return p.Name },
+			func(p Person, name string) Person {
+				return Person{Name: name, Age: p.Age}
+			},
+		)
+
+		// Base codec succeeds for any Person
+		baseCodec := MakeType(
+			"Person",
+			func(i any) validation.Result[Person] {
+				if p, ok := i.(Person); ok {
+					return validation.ToResult(validation.Success(p))
+				}
+				return validation.ToResult(validation.Failures[Person](validation.Errors{
+					&validation.ValidationError{Value: i, Messsage: "expected Person"},
+				}))
+			},
+			func(i any) Decode[Context, Person] {
+				return func(ctx Context) validation.Validation[Person] {
+					if p, ok := i.(Person); ok {
+						return validation.Success(p)
+					}
+					return validation.FailureWithMessage[Person](i, "expected Person")(ctx)
+				}
+			},
+			func(p Person) string { return "" },
+		)
+
+		// Kleisli arrow: the field codec receives the same input I (any = Person).
+		// It extracts the Name from the Person input.
+		// If the decoded struct's Age > 18, accept any name (including empty).
+		// If Age <= 18, reject empty names.
+		kleisli := func(p Person) Type[string, string, any] {
+			if p.Age > 18 {
+				// Adult: accept any name extracted from the Person input
+				return MakeType(
+					"AnyName",
+					func(i any) validation.Result[string] {
+						if person, ok := i.(Person); ok {
+							return validation.ToResult(validation.Success(person.Name))
+						}
+						return validation.ToResult(validation.Failures[string](validation.Errors{
+							&validation.ValidationError{Value: i, Messsage: "expected Person"},
+						}))
+					},
+					func(i any) Decode[Context, string] {
+						return func(ctx Context) validation.Validation[string] {
+							if person, ok := i.(Person); ok {
+								return validation.Success(person.Name)
+							}
+							return validation.FailureWithMessage[string](i, "expected Person")(ctx)
+						}
+					},
+					F.Identity[string],
+				)
+			}
+			// Minor: reject empty names
+			return MakeType(
+				"NonEmptyName",
+				func(i any) validation.Result[string] {
+					if person, ok := i.(Person); ok {
+						if person.Name != "" {
+							return validation.ToResult(validation.Success(person.Name))
+						}
+						return validation.ToResult(validation.Failures[string](validation.Errors{
+							&validation.ValidationError{Value: person.Name, Messsage: "name must not be empty for minors"},
+						}))
+					}
+					return validation.ToResult(validation.Failures[string](validation.Errors{
+						&validation.ValidationError{Value: i, Messsage: "expected Person"},
+					}))
+				},
+				func(i any) Decode[Context, string] {
+					return func(ctx Context) validation.Validation[string] {
+						if person, ok := i.(Person); ok {
+							if person.Name != "" {
+								return validation.Success(person.Name)
+							}
+							return validation.FailureWithMessage[string](person.Name, "name must not be empty for minors")(ctx)
+						}
+						return validation.FailureWithMessage[string](i, "expected Person")(ctx)
+					}
+				},
+				F.Identity[string],
+			)
+		}
+
+		operator := Bind(S.Monoid, nameLens, kleisli)
+		enhancedCodec := operator(baseCodec)
+
+		// Adult (Age=30) with empty name: should succeed (adult codec accepts any name)
+		adultPerson := Person{Name: "", Age: 30}
+		adultResult := enhancedCodec.Decode(adultPerson)
+		assert.True(t, either.IsRight(adultResult), "Adult should accept empty name")
+
+		// Minor (Age=15) with empty name: should fail (minor codec rejects empty names)
+		minorPerson := Person{Name: "", Age: 15}
+		minorResult := enhancedCodec.Decode(minorPerson)
+		assert.True(t, either.IsLeft(minorResult), "Minor with empty name should fail")
+
+		// Minor (Age=15) with non-empty name: should succeed
+		minorWithName := Person{Name: "Junior", Age: 15}
+		minorWithNameResult := enhancedCodec.Decode(minorWithName)
+		assert.True(t, either.IsRight(minorWithNameResult), "Minor with non-empty name should succeed")
+	})
+}

v2/optics/codec/codecs.go

@@ -343,6 +343,61 @@ func Int64FromString() Type[int64, string, string] {
 	)
 }
 
+// BoolFromString creates a bidirectional codec for parsing boolean values from strings.
+// This codec converts string representations of booleans to bool values and vice versa.
+//
+// The codec:
+//   - Decodes: Parses a string to a bool using strconv.ParseBool
+//   - Encodes: Converts a bool to its string representation using strconv.FormatBool
+//   - Validates: Ensures the string contains a valid boolean value
+//
+// The codec accepts the following string values (case-insensitive):
+//   - true: "1", "t", "T", "true", "TRUE", "True"
+//   - false: "0", "f", "F", "false", "FALSE", "False"
+//
+// Returns:
+//   - A Type[bool, string, string] codec that handles bool/string conversions
+//
+// Example:
+//
+//	boolCodec := BoolFromString()
+//
+//	// Decode valid boolean strings
+//	validation := boolCodec.Decode("true")
+//	// validation is Right(true)
+//
+//	validation := boolCodec.Decode("1")
+//	// validation is Right(true)
+//
+//	validation := boolCodec.Decode("false")
+//	// validation is Right(false)
+//
+//	validation := boolCodec.Decode("0")
+//	// validation is Right(false)
+//
+//	// Encode a boolean to string
+//	str := boolCodec.Encode(true)
+//	// str is "true"
+//
+//	str := boolCodec.Encode(false)
+//	// str is "false"
+//
+//	// Invalid boolean string fails validation
+//	validation := boolCodec.Decode("yes")
+//	// validation is Left(ValidationError{...})
+//
+//	// Case variations are accepted
+//	validation := boolCodec.Decode("TRUE")
+//	// validation is Right(true)
+func BoolFromString() Type[bool, string, string] {
+	return MakeType(
+		"BoolFromString",
+		Is[bool](),
+		validateFromParser(strconv.ParseBool),
+		strconv.FormatBool,
+	)
+}
+
 func decodeJSON[T any](dec json.Unmarshaler) ReaderResult[[]byte, T] {
 	return func(b []byte) Result[T] {
 		var t T

v2/optics/codec/codecs_test.go

@@ -461,6 +461,233 @@ func TestInt64FromString_Name(t *testing.T) {
 	assert.Equal(t, "Int64FromString", Int64FromString().Name())
 }
 
+// ---------------------------------------------------------------------------
+// BoolFromString
+// ---------------------------------------------------------------------------
+
+func TestBoolFromString_Decode_Success(t *testing.T) {
+	t.Run("decodes 'true' string", func(t *testing.T) {
+		c := BoolFromString()
+		result := c.Decode("true")
+		assert.Equal(t, validation.Success(true), result)
+	})
+
+	t.Run("decodes 'false' string", func(t *testing.T) {
+		c := BoolFromString()
+		result := c.Decode("false")
+		assert.Equal(t, validation.Success(false), result)
+	})
+
+	t.Run("decodes '1' as true", func(t *testing.T) {
+		c := BoolFromString()
+		result := c.Decode("1")
+		assert.Equal(t, validation.Success(true), result)
+	})
+
+	t.Run("decodes '0' as false", func(t *testing.T) {
+		c := BoolFromString()
+		result := c.Decode("0")
+		assert.Equal(t, validation.Success(false), result)
+	})
+
+	t.Run("decodes 't' as true", func(t *testing.T) {
+		c := BoolFromString()
+		result := c.Decode("t")
+		assert.Equal(t, validation.Success(true), result)
+	})
+
+	t.Run("decodes 'f' as false", func(t *testing.T) {
+		c := BoolFromString()
+		result := c.Decode("f")
+		assert.Equal(t, validation.Success(false), result)
+	})
+
+	t.Run("decodes 'T' as true", func(t *testing.T) {
+		c := BoolFromString()
+		result := c.Decode("T")
+		assert.Equal(t, validation.Success(true), result)
+	})
+
+	t.Run("decodes 'F' as false", func(t *testing.T) {
+		c := BoolFromString()
+		result := c.Decode("F")
+		assert.Equal(t, validation.Success(false), result)
+	})
+
+	t.Run("decodes 'TRUE' as true", func(t *testing.T) {
+		c := BoolFromString()
+		result := c.Decode("TRUE")
+		assert.Equal(t, validation.Success(true), result)
+	})
+
+	t.Run("decodes 'FALSE' as false", func(t *testing.T) {
+		c := BoolFromString()
+		result := c.Decode("FALSE")
+		assert.Equal(t, validation.Success(false), result)
+	})
+
+	t.Run("decodes 'True' as true", func(t *testing.T) {
+		c := BoolFromString()
+		result := c.Decode("True")
+		assert.Equal(t, validation.Success(true), result)
+	})
+
+	t.Run("decodes 'False' as false", func(t *testing.T) {
+		c := BoolFromString()
+		result := c.Decode("False")
+		assert.Equal(t, validation.Success(false), result)
+	})
+}
+
+func TestBoolFromString_Decode_Failure(t *testing.T) {
+	t.Run("fails on 'yes'", func(t *testing.T) {
+		c := BoolFromString()
+		result := c.Decode("yes")
+		assert.True(t, either.IsLeft(result))
+	})
+
+	t.Run("fails on 'no'", func(t *testing.T) {
+		c := BoolFromString()
+		result := c.Decode("no")
+		assert.True(t, either.IsLeft(result))
+	})
+
+	t.Run("fails on empty string", func(t *testing.T) {
+		c := BoolFromString()
+		result := c.Decode("")
+		assert.True(t, either.IsLeft(result))
+	})
+
+	t.Run("fails on numeric string other than 0 or 1", func(t *testing.T) {
+		c := BoolFromString()
+		result := c.Decode("2")
+		assert.True(t, either.IsLeft(result))
+	})
+
+	t.Run("fails on arbitrary text", func(t *testing.T) {
+		c := BoolFromString()
+		result := c.Decode("not a boolean")
+		assert.True(t, either.IsLeft(result))
+	})
+
+	t.Run("fails on whitespace", func(t *testing.T) {
+		c := BoolFromString()
+		result := c.Decode(" ")
+		assert.True(t, either.IsLeft(result))
+	})
+
+	t.Run("fails on 'true' with leading/trailing spaces", func(t *testing.T) {
+		c := BoolFromString()
+		result := c.Decode(" true ")
+		assert.True(t, either.IsLeft(result))
+	})
+}
+
+func TestBoolFromString_Encode(t *testing.T) {
+	t.Run("encodes true to 'true'", func(t *testing.T) {
+		c := BoolFromString()
+		assert.Equal(t, "true", c.Encode(true))
+	})
+
+	t.Run("encodes false to 'false'", func(t *testing.T) {
+		c := BoolFromString()
+		assert.Equal(t, "false", c.Encode(false))
+	})
+
+	t.Run("round-trip: decode 'true' then encode", func(t *testing.T) {
+		c := BoolFromString()
+		result := c.Decode("true")
+		require.True(t, either.IsRight(result))
+		b := either.MonadFold(result, func(validation.Errors) bool { return false }, func(b bool) bool { return b })
+		assert.Equal(t, "true", c.Encode(b))
+	})
+
+	t.Run("round-trip: decode 'false' then encode", func(t *testing.T) {
+		c := BoolFromString()
+		result := c.Decode("false")
+		require.True(t, either.IsRight(result))
+		b := either.MonadFold(result, func(validation.Errors) bool { return true }, func(b bool) bool { return b })
+		assert.Equal(t, "false", c.Encode(b))
+	})
+
+	t.Run("round-trip: decode '1' encodes as 'true'", func(t *testing.T) {
+		c := BoolFromString()
+		result := c.Decode("1")
+		require.True(t, either.IsRight(result))
+		b := either.MonadFold(result, func(validation.Errors) bool { return false }, func(b bool) bool { return b })
+		// Note: strconv.FormatBool always returns "true" or "false", not "1" or "0"
+		assert.Equal(t, "true", c.Encode(b))
+	})
+
+	t.Run("round-trip: decode '0' encodes as 'false'", func(t *testing.T) {
+		c := BoolFromString()
+		result := c.Decode("0")
+		require.True(t, either.IsRight(result))
+		b := either.MonadFold(result, func(validation.Errors) bool { return true }, func(b bool) bool { return b })
+		assert.Equal(t, "false", c.Encode(b))
+	})
+}
+
+func TestBoolFromString_EdgeCases(t *testing.T) {
+	t.Run("case sensitivity variations", func(t *testing.T) {
+		c := BoolFromString()
+		cases := []struct {
+			input    string
+			expected bool
+		}{
+			{"true", true},
+			{"True", true},
+			{"TRUE", true},
+			{"false", false},
+			{"False", false},
+			{"FALSE", false},
+			{"t", true},
+			{"T", true},
+			{"f", false},
+			{"F", false},
+		}
+		for _, tc := range cases {
+			result := c.Decode(tc.input)
+			require.True(t, either.IsRight(result), "expected success for %s", tc.input)
+			b := either.MonadFold(result, func(validation.Errors) bool { return !tc.expected }, func(b bool) bool { return b })
+			assert.Equal(t, tc.expected, b, "input: %s", tc.input)
+		}
+	})
+}
+
+func TestBoolFromString_Name(t *testing.T) {
+	assert.Equal(t, "BoolFromString", BoolFromString().Name())
+}
+
+func TestBoolFromString_Integration(t *testing.T) {
+	t.Run("decodes and encodes multiple boolean values", func(t *testing.T) {
+		c := BoolFromString()
+		cases := []struct {
+			str string
+			val bool
+		}{
+			{"true", true},
+			{"false", false},
+			{"1", true},
+			{"0", false},
+			{"T", true},
+			{"F", false},
+		}
+		for _, tc := range cases {
+			result := c.Decode(tc.str)
+			require.True(t, either.IsRight(result), "expected success for %s", tc.str)
+			b := either.MonadFold(result, func(validation.Errors) bool { return !tc.val }, func(b bool) bool { return b })
+			assert.Equal(t, tc.val, b)
+			// Note: encoding always produces "true" or "false", not the original input
+			if tc.val {
+				assert.Equal(t, "true", c.Encode(b))
+			} else {
+				assert.Equal(t, "false", c.Encode(b))
+			}
+		}
+	})
+}
+
 // ---------------------------------------------------------------------------
 // MarshalJSON
 // ---------------------------------------------------------------------------

v2/optics/codec/validation/types.go

@@ -259,5 +259,42 @@ type (
 	//	result := LetL(lens, double)(Success(21))   // Success(42)
 	Endomorphism[A any] = endomorphism.Endomorphism[A]
 
+	// Lazy represents a lazily-evaluated value of type A.
+	// This is an alias for lazy.Lazy[A], which defers computation until the value is needed.
+	//
+	// In the validation context, Lazy is used to defer expensive validation operations
+	// or to break circular dependencies in validation logic.
+	//
+	// Example:
+	//
+	//	lazyValidation := lazy.Of(func() Validation[int] {
+	//	    // Expensive validation logic here
+	//	    return Success(42)
+	//	})
+	//	// Validation is not executed until lazyValidation() is called
 	Lazy[A any] = lazy.Lazy[A]
+
+	// ErrorsProvider is an interface for types that can provide a collection of errors.
+	// This interface allows validation errors to be extracted from various error types
+	// in a uniform way, supporting error aggregation and reporting.
+	//
+	// Types implementing this interface can be unwrapped to access their underlying
+	// error collection, enabling consistent error handling across different error types.
+	//
+	// Example:
+	//
+	//	type MyErrors struct {
+	//	    errs []error
+	//	}
+	//
+	//	func (e *MyErrors) Errors() []error {
+	//	    return e.errs
+	//	}
+	//
+	//	// Usage
+	//	var provider ErrorsProvider = &MyErrors{errs: []error{...}}
+	//	allErrors := provider.Errors()
+	ErrorsProvider interface {
+		Errors() []error
+	}
 )

v2/optics/codec/validation/validation.go

@@ -3,6 +3,7 @@ package validation
 import (
 	"fmt"
 	"log/slog"
+	"strings"
 
 	A "github.com/IBM/fp-go/v2/array"
 	"github.com/IBM/fp-go/v2/either"
@@ -12,6 +13,11 @@ import (
 // Returns a generic error message indicating this is a validation error.
 // For detailed error information, use String() or Format() methods.
 
+// toError converts the validation error to the error interface
+func toError(v *ValidationError) error {
+	return v
+}
+
 // Error implements the error interface for ValidationError.
 // Returns a generic error message.
 func (v *ValidationError) Error() string {
@@ -34,44 +40,45 @@ func (v *ValidationError) String() string {
 // It includes the context path, message, and optionally the cause error.
 // Supports verbs: %s, %v, %+v (with additional details)
 func (v *ValidationError) Format(s fmt.State, verb rune) {
-	// Build the context path
-	path := ""
-	for i, entry := range v.Context {
-		if i > 0 {
-			path += "."
-		}
-		if entry.Key != "" {
-			path += entry.Key
-		} else {
-			path += entry.Type
-		}
-	}
+	var result strings.Builder
 
-	// Start with the path if available
-	result := ""
-	if path != "" {
-		result = fmt.Sprintf("at %s: ", path)
+	// Build the context path
+	if len(v.Context) > 0 {
+		var path strings.Builder
+		for i, entry := range v.Context {
+			if i > 0 {
+				path.WriteString(".")
+			}
+			if entry.Key != "" {
+				path.WriteString(entry.Key)
+			} else {
+				path.WriteString(entry.Type)
+			}
+		}
+		result.WriteString("at ")
+		result.WriteString(path.String())
+		result.WriteString(": ")
 	}
 
 	// Add the message
-	result += v.Messsage
+	result.WriteString(v.Messsage)
 
 	// Add the cause if present
 	if v.Cause != nil {
 		if s.Flag('+') && verb == 'v' {
 			// Verbose format with detailed cause
-			result += fmt.Sprintf("\n  caused by: %+v", v.Cause)
+			fmt.Fprintf(&result, "\n  caused by: %+v", v.Cause)
 		} else {
-			result += fmt.Sprintf(" (caused by: %v)", v.Cause)
+			fmt.Fprintf(&result, " (caused by: %v)", v.Cause)
 		}
 	}
 
 	// Add value information for verbose format
 	if s.Flag('+') && verb == 'v' {
-		result += fmt.Sprintf("\n  value: %#v", v.Value)
+		fmt.Fprintf(&result, "\n  value: %#v", v.Value)
 	}
 
-	fmt.Fprint(s, result)
+	fmt.Fprint(s, result.String())
 }
 
 // LogValue implements the slog.LogValuer interface for ValidationError.
@@ -94,18 +101,18 @@ func (v *ValidationError) LogValue() slog.Value {
 
 	// Add context path if available
 	if len(v.Context) > 0 {
-		path := ""
+		var path strings.Builder
 		for i, entry := range v.Context {
 			if i > 0 {
-				path += "."
+				path.WriteString(".")
 			}
 			if entry.Key != "" {
-				path += entry.Key
+				path.WriteString(entry.Key)
 			} else {
-				path += entry.Type
+				path.WriteString(entry.Type)
 			}
 		}
-		attrs = append(attrs, slog.String("path", path))
+		attrs = append(attrs, slog.String("path", path.String()))
 	}
 
 	// Add cause if present
@@ -119,13 +126,14 @@ func (v *ValidationError) LogValue() slog.Value {
 // Error implements the error interface for ValidationErrors.
 // Returns a generic error message indicating validation errors occurred.
 func (ve *validationErrors) Error() string {
-	if len(ve.errors) == 0 {
+	switch len(ve.errors) {
+	case 0:
 		return "ValidationErrors: no errors"
-	}
-	if len(ve.errors) == 1 {
+	case 1:
 		return "ValidationErrors: 1 error"
+	default:
+		return fmt.Sprintf("ValidationErrors: %d errors", len(ve.errors))
 	}
-	return fmt.Sprintf("ValidationErrors: %d errors", len(ve.errors))
 }
 
 // Unwrap returns the underlying cause error if present.
@@ -134,6 +142,33 @@ func (ve *validationErrors) Unwrap() error {
 	return ve.cause
 }
 
+// Errors implements the ErrorsProvider interface for validationErrors.
+// It converts the internal collection of ValidationError pointers to a slice of error interfaces.
+// This method enables uniform error extraction from validation error collections.
+//
+// The returned slice contains the same errors as the internal errors field,
+// but typed as error interface values for compatibility with standard Go error handling.
+//
+// Returns:
+//   - A slice of error interfaces, one for each ValidationError in the collection
+//
+// Example:
+//
+//	ve := &validationErrors{
+//	    errors: Errors{
+//	        &ValidationError{Messsage: "invalid email"},
+//	        &ValidationError{Messsage: "age must be positive"},
+//	    },
+//	}
+//	errs := ve.Errors()
+//	// errs is []error with 2 elements, each implementing the error interface
+//	for _, err := range errs {
+//	    fmt.Println(err.Error())  // "ValidationError"
+//	}
+func (ve *validationErrors) Errors() []error {
+	return A.MonadMap(ve.errors, toError)
+}
+
 // String returns a simple string representation of all validation errors.
 // Each error is listed on a separate line with its index.
 func (ve *validationErrors) String() string {
@@ -141,16 +176,17 @@ func (ve *validationErrors) String() string {
 		return "ValidationErrors: no errors"
 	}
 
-	result := fmt.Sprintf("ValidationErrors (%d):\n", len(ve.errors))
+	var result strings.Builder
+	fmt.Fprintf(&result, "ValidationErrors (%d):\n", len(ve.errors))
 	for i, err := range ve.errors {
-		result += fmt.Sprintf("  [%d] %s\n", i, err.String())
+		fmt.Fprintf(&result, "  [%d] %s\n", i, err.String())
 	}
 
 	if ve.cause != nil {
-		result += fmt.Sprintf("  caused by: %v\n", ve.cause)
+		fmt.Fprintf(&result, "  caused by: %v\n", ve.cause)
 	}
 
-	return result
+	return result.String()
 }
 
 // Format implements fmt.Formatter for custom formatting of ValidationErrors.

v2/optics/codec/validation/validation_test.go

@@ -846,3 +846,142 @@ func TestLogValuerInterface(t *testing.T) {
 		var _ slog.LogValuer = (*validationErrors)(nil)
 	})
 }
+
+// TestValidationErrors_Errors tests the Errors() method implementation
+func TestValidationErrors_Errors(t *testing.T) {
+	t.Run("returns empty slice for no errors", func(t *testing.T) {
+		ve := &validationErrors{
+			errors: Errors{},
+		}
+
+		errs := ve.Errors()
+		assert.Empty(t, errs)
+		assert.NotNil(t, errs)
+	})
+
+	t.Run("converts single ValidationError to error interface", func(t *testing.T) {
+		ve := &validationErrors{
+			errors: Errors{
+				&ValidationError{Value: "test", Messsage: "invalid value"},
+			},
+		}
+
+		errs := ve.Errors()
+		require.Len(t, errs, 1)
+		assert.Equal(t, "ValidationError", errs[0].Error())
+	})
+
+	t.Run("converts multiple ValidationErrors to error interfaces", func(t *testing.T) {
+		ve := &validationErrors{
+			errors: Errors{
+				&ValidationError{Value: "test1", Messsage: "error 1"},
+				&ValidationError{Value: "test2", Messsage: "error 2"},
+				&ValidationError{Value: "test3", Messsage: "error 3"},
+			},
+		}
+
+		errs := ve.Errors()
+		require.Len(t, errs, 3)
+		for _, err := range errs {
+			assert.Equal(t, "ValidationError", err.Error())
+		}
+	})
+
+	t.Run("preserves error details in converted errors", func(t *testing.T) {
+		originalErr := &ValidationError{
+			Value:    "abc",
+			Context:  []ContextEntry{{Key: "field"}},
+			Messsage: "invalid format",
+			Cause:    errors.New("parse error"),
+		}
+		ve := &validationErrors{
+			errors: Errors{originalErr},
+		}
+
+		errs := ve.Errors()
+		require.Len(t, errs, 1)
+
+		// Verify the error can be type-asserted back to ValidationError
+		validationErr, ok := errs[0].(*ValidationError)
+		require.True(t, ok)
+		assert.Equal(t, "abc", validationErr.Value)
+		assert.Equal(t, "invalid format", validationErr.Messsage)
+		assert.NotNil(t, validationErr.Cause)
+		assert.Len(t, validationErr.Context, 1)
+	})
+
+	t.Run("implements ErrorsProvider interface", func(t *testing.T) {
+		ve := &validationErrors{
+			errors: Errors{
+				&ValidationError{Messsage: "error 1"},
+				&ValidationError{Messsage: "error 2"},
+			},
+		}
+
+		// Verify it implements ErrorsProvider
+		var provider ErrorsProvider = ve
+		errs := provider.Errors()
+		assert.Len(t, errs, 2)
+	})
+
+	t.Run("returned errors are usable with standard error handling", func(t *testing.T) {
+		cause := errors.New("underlying error")
+		ve := &validationErrors{
+			errors: Errors{
+				&ValidationError{
+					Value:    "test",
+					Messsage: "validation failed",
+					Cause:    cause,
+				},
+			},
+		}
+
+		errs := ve.Errors()
+		require.Len(t, errs, 1)
+
+		// Test with errors.Is
+		assert.True(t, errors.Is(errs[0], cause))
+
+		// Test with errors.As
+		var validationErr *ValidationError
+		assert.True(t, errors.As(errs[0], &validationErr))
+		assert.Equal(t, "validation failed", validationErr.Messsage)
+	})
+
+	t.Run("does not modify original errors slice", func(t *testing.T) {
+		originalErrors := Errors{
+			&ValidationError{Value: "test1", Messsage: "error 1"},
+			&ValidationError{Value: "test2", Messsage: "error 2"},
+		}
+		ve := &validationErrors{
+			errors: originalErrors,
+		}
+
+		errs := ve.Errors()
+		require.Len(t, errs, 2)
+
+		// Original should be unchanged
+		assert.Len(t, ve.errors, 2)
+		assert.Equal(t, originalErrors, ve.errors)
+	})
+
+	t.Run("each error in slice is independent", func(t *testing.T) {
+		ve := &validationErrors{
+			errors: Errors{
+				&ValidationError{Value: "test1", Messsage: "error 1"},
+				&ValidationError{Value: "test2", Messsage: "error 2"},
+			},
+		}
+
+		errs := ve.Errors()
+		require.Len(t, errs, 2)
+
+		// Verify each error is distinct
+		err1, ok1 := errs[0].(*ValidationError)
+		err2, ok2 := errs[1].(*ValidationError)
+		require.True(t, ok1)
+		require.True(t, ok2)
+		assert.NotEqual(t, err1.Messsage, err2.Messsage)
+		assert.NotEqual(t, err1.Value, err2.Value)
+	})
+}

v2/readerio/bracket.go

@@ -1,6 +1,7 @@
 package readerio
 
 import (
+	"github.com/IBM/fp-go/v2/function"
 	G "github.com/IBM/fp-go/v2/internal/bracket"
 )
 
@@ -30,3 +31,10 @@ func Bracket[
 		release,
 	)
 }
+
+//go:inline
+func WithResource[R, A, B, ANY any](
+	onCreate ReaderIO[R, A], onRelease Kleisli[R, A, ANY]) Kleisli[R, Kleisli[R, A, B], B] {
+
+	return function.Bind13of3(Bracket[R, A, B, ANY])(onCreate, function.Ignore2of2[B](onRelease))
+}