fix: parameter order for Local and TapIOK

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

v2/effect/common_test.go

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

v2/effect/dependencies.go

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

v2/effect/dependencies_test.go

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

v2/effect/effect.go

@@ -20,6 +20,7 @@ import (
 	"github.com/IBM/fp-go/v2/context/readerreaderioresult"
 	"github.com/IBM/fp-go/v2/function"
 	"github.com/IBM/fp-go/v2/internal/fromreader"
+	"github.com/IBM/fp-go/v2/io"
 	"github.com/IBM/fp-go/v2/reader"
 	"github.com/IBM/fp-go/v2/readerio"
 	"github.com/IBM/fp-go/v2/result"
@@ -187,10 +188,121 @@ func Map[C, A, B any](f func(A) B) Operator[C, A, B] {
 //		return effect.Of[MyContext](strconv.Itoa(x * 2))
 //	})(eff)
 //	// chained produces "84"
+//
+//go:inline
 func Chain[C, A, B any](f Kleisli[C, A, B]) Operator[C, A, B] {
 	return readerreaderioresult.Chain(f)
 }
 
+// ChainIOK chains an effect with a function that returns an IO action.
+// This is useful for integrating IO-based computations (synchronous side effects)
+// into effect chains. The IO action is automatically lifted into the Effect context.
+//
+// # Type Parameters
+//
+//   - C: The context type required by the effect
+//   - A: The input value type
+//   - B: The output value type
+//
+// # Parameters
+//
+//   - f: A function that takes A and returns IO[B]
+//
+// # Returns
+//
+//   - Operator[C, A, B]: A function that chains the IO-returning function with the effect
+//
+// # Example
+//
+//	performIO := func(n int) io.IO[string] {
+//	    return func() string {
+//	        // Perform synchronous side effect
+//	        return fmt.Sprintf("Value: %d", n)
+//	    }
+//	}
+//
+//	eff := effect.Of[MyContext](42)
+//	chained := effect.ChainIOK[MyContext](performIO)(eff)
+//	// chained produces "Value: 42"
+//
+//go:inline
+func ChainIOK[C, A, B any](f io.Kleisli[A, B]) Operator[C, A, B] {
+	return readerreaderioresult.ChainIOK[C](f)
+}
+
+// ChainFirstIOK chains an effect with a function that returns an IO action,
+// but discards the result and returns the original value.
+// This is useful for performing side effects (like logging) without changing the value.
+//
+// # Type Parameters
+//
+//   - C: The context type required by the effect
+//   - A: The value type (preserved)
+//   - B: The type produced by the IO action (discarded)
+//
+// # Parameters
+//
+//   - f: A function that takes A and returns IO[B] for side effects
+//
+// # Returns
+//
+//   - Operator[C, A, A]: A function that executes the IO action but preserves the original value
+//
+// # Example
+//
+//	logValue := func(n int) io.IO[any] {
+//	    return func() any {
+//	        fmt.Printf("Processing: %d\n", n)
+//	        return nil
+//	    }
+//	}
+//
+//	eff := effect.Of[MyContext](42)
+//	logged := effect.ChainFirstIOK[MyContext](logValue)(eff)
+//	// Prints "Processing: 42" but still produces 42
+//
+//go:inline
+func ChainFirstIOK[C, A, B any](f io.Kleisli[A, B]) Operator[C, A, A] {
+	return readerreaderioresult.ChainFirstIOK[C](f)
+}
+
+// TapIOK is an alias for ChainFirstIOK.
+// It chains an effect with a function that returns an IO action for side effects,
+// but preserves the original value. This is useful for logging, debugging, or
+// performing actions without changing the result.
+//
+// # Type Parameters
+//
+//   - C: The context type required by the effect
+//   - A: The value type (preserved)
+//   - B: The type produced by the IO action (discarded)
+//
+// # Parameters
+//
+//   - f: A function that takes A and returns IO[B] for side effects
+//
+// # Returns
+//
+//   - Operator[C, A, A]: A function that executes the IO action but preserves the original value
+//
+// # Example
+//
+//	logValue := func(n int) io.IO[any] {
+//	    return func() any {
+//	        fmt.Printf("Value: %d\n", n)
+//	        return nil
+//	    }
+//	}
+//
+//	eff := effect.Of[MyContext](42)
+//	tapped := effect.TapIOK[MyContext](logValue)(eff)
+//	// Prints "Value: 42" but still produces 42
+//
+//go:inline
+func TapIOK[C, A, B any](f io.Kleisli[A, B]) Operator[C, A, A] {
+	return readerreaderioresult.ChainFirstIOK[C](f)
+}
+
 // Ap applies a function wrapped in an Effect to a value wrapped in an Effect.
 // This is the applicative apply operation, useful for applying effects in parallel.
 //

v2/effect/effect_additional_test.go

@@ -0,0 +1,651 @@
+// Copyright (c) 2023 - 2025 IBM Corp.
+// All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package effect
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"strconv"
+	"testing"
+
+	F "github.com/IBM/fp-go/v2/function"
+	"github.com/IBM/fp-go/v2/io"
+	"github.com/IBM/fp-go/v2/reader"
+	"github.com/IBM/fp-go/v2/result"
+	"github.com/stretchr/testify/assert"
+)
+
+// TestSucceed tests the Succeed function
+func TestSucceed_Success(t *testing.T) {
+	t.Run("creates successful effect with int", func(t *testing.T) {
+		eff := Succeed[TestConfig](42)
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Of(42), outcome)
+	})
+
+	t.Run("creates successful effect with string", func(t *testing.T) {
+		eff := Succeed[TestConfig]("hello")
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Of("hello"), outcome)
+	})
+
+	t.Run("creates successful effect with zero value", func(t *testing.T) {
+		eff := Succeed[TestConfig](0)
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Of(0), outcome)
+	})
+}
+
+// TestFail tests the Fail function
+func TestFail_Failure(t *testing.T) {
+	t.Run("creates failed effect with error", func(t *testing.T) {
+		testErr := errors.New("test error")
+		eff := Fail[TestConfig, int](testErr)
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Left[int](testErr), outcome)
+	})
+
+	t.Run("preserves error message", func(t *testing.T) {
+		testErr := errors.New("specific error message")
+		eff := Fail[TestConfig, string](testErr)
+		outcome := eff(testConfig)(context.Background())()
+		assert.True(t, result.IsLeft(outcome))
+		extractedErr := result.MonadFold(outcome,
+			F.Identity[error],
+			func(string) error { return nil },
+		)
+		assert.Equal(t, testErr, extractedErr)
+	})
+}
+
+// TestOf tests the Of function
+func TestOf_Success(t *testing.T) {
+	t.Run("creates successful effect with value", func(t *testing.T) {
+		eff := Of[TestConfig](100)
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Of(100), outcome)
+	})
+
+	t.Run("is equivalent to Succeed", func(t *testing.T) {
+		value := "test"
+		eff1 := Of[TestConfig](value)
+		eff2 := Succeed[TestConfig](value)
+		outcome1 := eff1(testConfig)(context.Background())()
+		outcome2 := eff2(testConfig)(context.Background())()
+		assert.Equal(t, outcome1, outcome2)
+	})
+}
+
+// TestMap tests the Map function
+func TestMap_Success(t *testing.T) {
+	t.Run("transforms success value", func(t *testing.T) {
+		eff := F.Pipe1(
+			Of[TestConfig](42),
+			Map[TestConfig](func(x int) int { return x * 2 }),
+		)
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Of(84), outcome)
+	})
+
+	t.Run("transforms type", func(t *testing.T) {
+		eff := F.Pipe1(
+			Of[TestConfig](42),
+			Map[TestConfig](func(x int) string { return strconv.Itoa(x) }),
+		)
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Of("42"), outcome)
+	})
+
+	t.Run("chains multiple maps", func(t *testing.T) {
+		eff := F.Pipe2(
+			Of[TestConfig](10),
+			Map[TestConfig](func(x int) int { return x + 5 }),
+			Map[TestConfig](func(x int) int { return x * 2 }),
+		)
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Of(30), outcome)
+	})
+}
+
+func TestMap_Failure(t *testing.T) {
+	t.Run("propagates error unchanged", func(t *testing.T) {
+		testErr := errors.New("test error")
+		eff := F.Pipe1(
+			Fail[TestConfig, int](testErr),
+			Map[TestConfig](func(x int) int { return x * 2 }),
+		)
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Left[int](testErr), outcome)
+	})
+}
+
+// TestChain tests the Chain function
+func TestChain_Success(t *testing.T) {
+	t.Run("sequences two effects", func(t *testing.T) {
+		eff := F.Pipe1(
+			Of[TestConfig](42),
+			Chain[TestConfig](func(x int) Effect[TestConfig, string] {
+				return Of[TestConfig](strconv.Itoa(x))
+			}),
+		)
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Of("42"), outcome)
+	})
+
+	t.Run("chains multiple effects", func(t *testing.T) {
+		eff := F.Pipe2(
+			Of[TestConfig](10),
+			Chain[TestConfig](func(x int) Effect[TestConfig, int] {
+				return Of[TestConfig](x + 5)
+			}),
+			Chain[TestConfig](func(x int) Effect[TestConfig, int] {
+				return Of[TestConfig](x * 2)
+			}),
+		)
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Of(30), outcome)
+	})
+}
+
+func TestChain_Failure(t *testing.T) {
+	t.Run("propagates error from first effect", func(t *testing.T) {
+		testErr := errors.New("first error")
+		eff := F.Pipe1(
+			Fail[TestConfig, int](testErr),
+			Chain[TestConfig](func(x int) Effect[TestConfig, string] {
+				return Of[TestConfig]("should not execute")
+			}),
+		)
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Left[string](testErr), outcome)
+	})
+
+	t.Run("propagates error from second effect", func(t *testing.T) {
+		testErr := errors.New("second error")
+		eff := F.Pipe1(
+			Of[TestConfig](42),
+			Chain[TestConfig](func(x int) Effect[TestConfig, string] {
+				return Fail[TestConfig, string](testErr)
+			}),
+		)
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Left[string](testErr), outcome)
+	})
+}
+
+// TestChainIOK tests the ChainIOK function
+func TestChainIOK_Success(t *testing.T) {
+	t.Run("chains with IO action", func(t *testing.T) {
+		counter := 0
+		eff := F.Pipe1(
+			Of[TestConfig](42),
+			ChainIOK[TestConfig](func(x int) io.IO[string] {
+				return func() string {
+					counter++
+					return fmt.Sprintf("Value: %d", x)
+				}
+			}),
+		)
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Of("Value: 42"), outcome)
+		assert.Equal(t, 1, counter)
+	})
+
+	t.Run("chains multiple IO actions", func(t *testing.T) {
+		log := []string{}
+		eff := F.Pipe2(
+			Of[TestConfig](10),
+			ChainIOK[TestConfig](func(x int) io.IO[int] {
+				return func() int {
+					log = append(log, "first")
+					return x + 5
+				}
+			}),
+			ChainIOK[TestConfig](func(x int) io.IO[int] {
+				return func() int {
+					log = append(log, "second")
+					return x * 2
+				}
+			}),
+		)
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Of(30), outcome)
+		assert.Equal(t, []string{"first", "second"}, log)
+	})
+}
+
+func TestChainIOK_Failure(t *testing.T) {
+	t.Run("propagates error from previous effect", func(t *testing.T) {
+		testErr := errors.New("test error")
+		executed := false
+		eff := F.Pipe1(
+			Fail[TestConfig, int](testErr),
+			ChainIOK[TestConfig](func(x int) io.IO[string] {
+				return func() string {
+					executed = true
+					return "should not execute"
+				}
+			}),
+		)
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Left[string](testErr), outcome)
+		assert.False(t, executed)
+	})
+}
+
+// TestChainFirstIOK tests the ChainFirstIOK function
+func TestChainFirstIOK_Success(t *testing.T) {
+	t.Run("executes IO but preserves value", func(t *testing.T) {
+		log := []string{}
+		eff := F.Pipe1(
+			Of[TestConfig](42),
+			ChainFirstIOK[TestConfig](func(x int) io.IO[any] {
+				return func() any {
+					log = append(log, fmt.Sprintf("logged: %d", x))
+					return nil
+				}
+			}),
+		)
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Of(42), outcome)
+		assert.Equal(t, []string{"logged: 42"}, log)
+	})
+
+	t.Run("chains multiple side effects", func(t *testing.T) {
+		log := []string{}
+		eff := F.Pipe2(
+			Of[TestConfig](10),
+			ChainFirstIOK[TestConfig](func(x int) io.IO[any] {
+				return func() any {
+					log = append(log, "first")
+					return nil
+				}
+			}),
+			ChainFirstIOK[TestConfig](func(x int) io.IO[any] {
+				return func() any {
+					log = append(log, "second")
+					return nil
+				}
+			}),
+		)
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Of(10), outcome)
+		assert.Equal(t, []string{"first", "second"}, log)
+	})
+}
+
+func TestChainFirstIOK_Failure(t *testing.T) {
+	t.Run("propagates error without executing IO", func(t *testing.T) {
+		testErr := errors.New("test error")
+		executed := false
+		eff := F.Pipe1(
+			Fail[TestConfig, int](testErr),
+			ChainFirstIOK[TestConfig](func(x int) io.IO[any] {
+				return func() any {
+					executed = true
+					return nil
+				}
+			}),
+		)
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Left[int](testErr), outcome)
+		assert.False(t, executed)
+	})
+}
+
+// TestTapIOK tests the TapIOK function
+func TestTapIOK_Success(t *testing.T) {
+	t.Run("executes IO but preserves value", func(t *testing.T) {
+		log := []string{}
+		eff := F.Pipe1(
+			Of[TestConfig](42),
+			TapIOK[TestConfig](func(x int) io.IO[any] {
+				return func() any {
+					log = append(log, fmt.Sprintf("tapped: %d", x))
+					return nil
+				}
+			}),
+		)
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Of(42), outcome)
+		assert.Equal(t, []string{"tapped: 42"}, log)
+	})
+
+	t.Run("is equivalent to ChainFirstIOK", func(t *testing.T) {
+		log1 := []string{}
+		log2 := []string{}
+
+		eff1 := F.Pipe1(
+			Of[TestConfig](10),
+			TapIOK[TestConfig](func(x int) io.IO[any] {
+				return func() any {
+					log1 = append(log1, "tap")
+					return nil
+				}
+			}),
+		)
+
+		eff2 := F.Pipe1(
+			Of[TestConfig](10),
+			ChainFirstIOK[TestConfig](func(x int) io.IO[any] {
+				return func() any {
+					log2 = append(log2, "tap")
+					return nil
+				}
+			}),
+		)
+
+		outcome1 := eff1(testConfig)(context.Background())()
+		outcome2 := eff2(testConfig)(context.Background())()
+
+		assert.Equal(t, outcome1, outcome2)
+		assert.Equal(t, log1, log2)
+	})
+}
+
+func TestTapIOK_Failure(t *testing.T) {
+	t.Run("propagates error without executing IO", func(t *testing.T) {
+		testErr := errors.New("test error")
+		executed := false
+		eff := F.Pipe1(
+			Fail[TestConfig, int](testErr),
+			TapIOK[TestConfig](func(x int) io.IO[any] {
+				return func() any {
+					executed = true
+					return nil
+				}
+			}),
+		)
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Left[int](testErr), outcome)
+		assert.False(t, executed)
+	})
+}
+
+// TestChainResultK tests the ChainResultK function
+func TestChainResultK_Success(t *testing.T) {
+	t.Run("chains with Result-returning function", func(t *testing.T) {
+		parseIntResult := result.Eitherize1(strconv.Atoi)
+		eff := F.Pipe1(
+			Of[TestConfig]("42"),
+			ChainResultK[TestConfig](parseIntResult),
+		)
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Of(42), outcome)
+	})
+
+	t.Run("chains multiple Result operations", func(t *testing.T) {
+		parseIntResult := result.Eitherize1(strconv.Atoi)
+		eff := F.Pipe2(
+			Of[TestConfig]("10"),
+			ChainResultK[TestConfig](parseIntResult),
+			ChainResultK[TestConfig](func(x int) result.Result[string] {
+				return result.Of(fmt.Sprintf("Value: %d", x*2))
+			}),
+		)
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Of("Value: 20"), outcome)
+	})
+}
+
+func TestChainResultK_Failure(t *testing.T) {
+	t.Run("propagates error from previous effect", func(t *testing.T) {
+		testErr := errors.New("test error")
+		parseIntResult := result.Eitherize1(strconv.Atoi)
+		eff := F.Pipe1(
+			Fail[TestConfig, string](testErr),
+			ChainResultK[TestConfig](parseIntResult),
+		)
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Left[int](testErr), outcome)
+	})
+
+	t.Run("propagates error from Result function", func(t *testing.T) {
+		parseIntResult := result.Eitherize1(strconv.Atoi)
+		eff := F.Pipe1(
+			Of[TestConfig]("not a number"),
+			ChainResultK[TestConfig](parseIntResult),
+		)
+		outcome := eff(testConfig)(context.Background())()
+		assert.True(t, result.IsLeft(outcome))
+	})
+}
+
+// TestAp tests the Ap function
+func TestAp_Success(t *testing.T) {
+	t.Run("applies function effect to value effect", func(t *testing.T) {
+		fnEff := Of[TestConfig](func(x int) int { return x * 2 })
+		valEff := Of[TestConfig](21)
+		eff := Ap[int](valEff)(fnEff)
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Of(42), outcome)
+	})
+
+	t.Run("applies function with different types", func(t *testing.T) {
+		fnEff := Of[TestConfig](func(x int) string { return strconv.Itoa(x) })
+		valEff := Of[TestConfig](42)
+		eff := Ap[string](valEff)(fnEff)
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Of("42"), outcome)
+	})
+}
+
+func TestAp_Failure(t *testing.T) {
+	t.Run("propagates error from function effect", func(t *testing.T) {
+		testErr := errors.New("function error")
+		fnEff := Fail[TestConfig, func(int) int](testErr)
+		valEff := Of[TestConfig](42)
+		eff := Ap[int](valEff)(fnEff)
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Left[int](testErr), outcome)
+	})
+
+	t.Run("propagates error from value effect", func(t *testing.T) {
+		testErr := errors.New("value error")
+		fnEff := Of[TestConfig](func(x int) int { return x * 2 })
+		valEff := Fail[TestConfig, int](testErr)
+		eff := Ap[int](valEff)(fnEff)
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Left[int](testErr), outcome)
+	})
+}
+
+// TestSuspend tests the Suspend function
+func TestSuspend_Success(t *testing.T) {
+	t.Run("delays evaluation of effect", func(t *testing.T) {
+		counter := 0
+		eff := Suspend(func() Effect[TestConfig, int] {
+			counter++
+			return Of[TestConfig](42)
+		})
+		assert.Equal(t, 0, counter, "should not evaluate immediately")
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, 1, counter, "should evaluate when run")
+		assert.Equal(t, result.Of(42), outcome)
+	})
+
+	t.Run("enables recursive effects", func(t *testing.T) {
+		var factorial func(int) Effect[TestConfig, int]
+		factorial = func(n int) Effect[TestConfig, int] {
+			if n <= 1 {
+				return Of[TestConfig](1)
+			}
+			return Suspend(func() Effect[TestConfig, int] {
+				return F.Pipe1(
+					factorial(n-1),
+					Map[TestConfig](func(x int) int { return x * n }),
+				)
+			})
+		}
+
+		outcome := factorial(5)(testConfig)(context.Background())()
+		assert.Equal(t, result.Of(120), outcome)
+	})
+}
+
+// TestTap tests the Tap function
+func TestTap_Success(t *testing.T) {
+	t.Run("executes side effect but preserves value", func(t *testing.T) {
+		log := []string{}
+		eff := F.Pipe1(
+			Of[TestConfig](42),
+			Tap[TestConfig](func(x int) Effect[TestConfig, any] {
+				log = append(log, fmt.Sprintf("tapped: %d", x))
+				return Of[TestConfig, any](nil)
+			}),
+		)
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Of(42), outcome)
+		assert.Equal(t, []string{"tapped: 42"}, log)
+	})
+
+	t.Run("chains multiple taps", func(t *testing.T) {
+		log := []string{}
+		eff := F.Pipe2(
+			Of[TestConfig](10),
+			Tap[TestConfig](func(x int) Effect[TestConfig, any] {
+				log = append(log, "first")
+				return Of[TestConfig, any](nil)
+			}),
+			Tap[TestConfig](func(x int) Effect[TestConfig, any] {
+				log = append(log, "second")
+				return Of[TestConfig, any](nil)
+			}),
+		)
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Of(10), outcome)
+		assert.Equal(t, []string{"first", "second"}, log)
+	})
+}
+
+func TestTap_Failure(t *testing.T) {
+	t.Run("propagates error without executing tap", func(t *testing.T) {
+		testErr := errors.New("test error")
+		executed := false
+		eff := F.Pipe1(
+			Fail[TestConfig, int](testErr),
+			Tap[TestConfig](func(x int) Effect[TestConfig, any] {
+				executed = true
+				return Of[TestConfig, any](nil)
+			}),
+		)
+		outcome := eff(testConfig)(context.Background())()
+		assert.Equal(t, result.Left[int](testErr), outcome)
+		assert.False(t, executed)
+	})
+}
+
+// TestTernary tests the Ternary function
+func TestTernary_Success(t *testing.T) {
+	t.Run("executes onTrue when predicate is true", func(t *testing.T) {
+		kleisli := Ternary(
+			func(x int) bool { return x > 10 },
+			func(x int) Effect[TestConfig, string] {
+				return Of[TestConfig]("large")
+			},
+			func(x int) Effect[TestConfig, string] {
+				return Of[TestConfig]("small")
+			},
+		)
+		outcome := kleisli(15)(testConfig)(context.Background())()
+		assert.Equal(t, result.Of("large"), outcome)
+	})
+
+	t.Run("executes onFalse when predicate is false", func(t *testing.T) {
+		kleisli := Ternary(
+			func(x int) bool { return x > 10 },
+			func(x int) Effect[TestConfig, string] {
+				return Of[TestConfig]("large")
+			},
+			func(x int) Effect[TestConfig, string] {
+				return Of[TestConfig]("small")
+			},
+		)
+		outcome := kleisli(5)(testConfig)(context.Background())()
+		assert.Equal(t, result.Of("small"), outcome)
+	})
+
+	t.Run("works with boundary value", func(t *testing.T) {
+		kleisli := Ternary(
+			func(x int) bool { return x >= 10 },
+			func(x int) Effect[TestConfig, string] {
+				return Of[TestConfig]("gte")
+			},
+			func(x int) Effect[TestConfig, string] {
+				return Of[TestConfig]("lt")
+			},
+		)
+		outcome := kleisli(10)(testConfig)(context.Background())()
+		assert.Equal(t, result.Of("gte"), outcome)
+	})
+}
+
+// TestRead tests the Read function
+func TestRead_Success(t *testing.T) {
+	t.Run("provides context to effect", func(t *testing.T) {
+		eff := Of[TestConfig](42)
+		thunk := Read[int](testConfig)(eff)
+		outcome := thunk(context.Background())()
+		assert.Equal(t, result.Of(42), outcome)
+	})
+
+	t.Run("converts effect to thunk", func(t *testing.T) {
+		eff := F.Pipe1(
+			Of[TestConfig](10),
+			Map[TestConfig](func(x int) int { return x * testConfig.Multiplier }),
+		)
+		thunk := Read[int](testConfig)(eff)
+		outcome := thunk(context.Background())()
+		assert.Equal(t, result.Of(30), outcome)
+	})
+
+	t.Run("works with different contexts", func(t *testing.T) {
+		cfg1 := TestConfig{Multiplier: 2, Prefix: "A", DatabaseURL: ""}
+		cfg2 := TestConfig{Multiplier: 5, Prefix: "B", DatabaseURL: ""}
+
+		// Create an effect that uses the context's Multiplier
+		eff := F.Pipe1(
+			Of[TestConfig](10),
+			ChainReaderK[TestConfig](func(x int) reader.Reader[TestConfig, int] {
+				return func(cfg TestConfig) int {
+					return x * cfg.Multiplier
+				}
+			}),
+		)
+
+		thunk1 := Read[int](cfg1)(eff)
+		thunk2 := Read[int](cfg2)(eff)
+
+		outcome1 := thunk1(context.Background())()
+		outcome2 := thunk2(context.Background())()
+
+		assert.Equal(t, result.Of(20), outcome1)
+		assert.Equal(t, result.Of(50), outcome2)
+	})
+}
+
+func TestRead_Failure(t *testing.T) {
+	t.Run("propagates error from effect", func(t *testing.T) {
+		testErr := errors.New("test error")
+		eff := Fail[TestConfig, int](testErr)
+		thunk := Read[int](testConfig)(eff)
+		outcome := thunk(context.Background())()
+		assert.Equal(t, result.Left[int](testErr), outcome)
+	})
+}
+
+// Made with Bob

v2/effect/run.go

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

v2/effect/run_test.go

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