fix: implement BindReaderK

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

v2/internal/fromeither/either.go

@@ -22,10 +22,12 @@ import (
 	O "github.com/IBM/fp-go/v2/option"
 )
 
+//go:inline
 func FromOption[A, HKTEA, E any](fromEither func(ET.Either[E, A]) HKTEA, onNone func() E) func(ma O.Option[A]) HKTEA {
 	return F.Flow2(ET.FromOption[A](onNone), fromEither)
 }
 
+//go:inline
 func FromPredicate[E, A, HKTEA any](fromEither func(ET.Either[E, A]) HKTEA, pred func(A) bool, onFalse func(A) E) func(A) HKTEA {
 	return F.Flow2(ET.FromPredicate(pred, onFalse), fromEither)
 }
@@ -45,6 +47,7 @@ func MonadFromOption[E, A, HKTEA any](
 	)
 }
 
+//go:inline
 func FromOptionK[A, E, B, HKTEB any](
 	fromEither func(ET.Either[E, B]) HKTEB,
 	onNone func() E) func(f func(A) O.Option[B]) func(A) HKTEB {
@@ -52,6 +55,7 @@ func FromOptionK[A, E, B, HKTEB any](
 	return F.Bind2nd(F.Flow2[func(A) O.Option[B], func(O.Option[B]) HKTEB, A, O.Option[B], HKTEB], FromOption(fromEither, onNone))
 }
 
+//go:inline
 func MonadChainEitherK[A, E, B, HKTEA, HKTEB any](
 	mchain func(HKTEA, func(A) HKTEB) HKTEB,
 	fromEither func(ET.Either[E, B]) HKTEB,
@@ -60,6 +64,7 @@ func MonadChainEitherK[A, E, B, HKTEA, HKTEB any](
 	return mchain(ma, F.Flow2(f, fromEither))
 }
 
+//go:inline
 func ChainEitherK[A, E, B, HKTEA, HKTEB any](
 	mchain func(func(A) HKTEB) func(HKTEA) HKTEB,
 	fromEither func(ET.Either[E, B]) HKTEB,
@@ -67,6 +72,7 @@ func ChainEitherK[A, E, B, HKTEA, HKTEB any](
 	return mchain(F.Flow2(f, fromEither))
 }
 
+//go:inline
 func ChainOptionK[A, E, B, HKTEA, HKTEB any](
 	mchain func(HKTEA, func(A) HKTEB) HKTEB,
 	fromEither func(ET.Either[E, B]) HKTEB,
@@ -75,6 +81,7 @@ func ChainOptionK[A, E, B, HKTEA, HKTEB any](
 	return F.Flow2(FromOptionK[A](fromEither, onNone), F.Bind1st(F.Bind2nd[HKTEA, func(A) HKTEB, HKTEB], mchain))
 }
 
+//go:inline
 func MonadChainFirstEitherK[A, E, B, HKTEA, HKTEB any](
 	mchain func(HKTEA, func(A) HKTEA) HKTEA,
 	mmap func(HKTEB, func(B) A) HKTEA,
@@ -84,6 +91,7 @@ func MonadChainFirstEitherK[A, E, B, HKTEA, HKTEB any](
 	return C.MonadChainFirst(mchain, mmap, ma, F.Flow2(f, fromEither))
 }
 
+//go:inline
 func ChainFirstEitherK[A, E, B, HKTEA, HKTEB any](
 	mchain func(func(A) HKTEA) func(HKTEA) HKTEA,
 	mmap func(func(B) A) func(HKTEB) HKTEA,
@@ -91,3 +99,23 @@ func ChainFirstEitherK[A, E, B, HKTEA, HKTEB any](
 	f func(A) ET.Either[E, B]) func(HKTEA) HKTEA {
 	return C.ChainFirst(mchain, mmap, F.Flow2(f, fromEither))
 }
+
+//go:inline
+func BindEitherK[
+	E, S1, S2, T,
+	HKTET,
+	HKTES1,
+	HKTES2 any](
+	mchain func(func(S1) HKTES2) func(HKTES1) HKTES2,
+	mmap func(func(T) S2) func(HKTET) HKTES2,
+	fromEither func(ET.Either[E, T]) HKTET,
+	setter func(T) func(S1) S2,
+	f func(S1) ET.Either[E, T],
+) func(HKTES1) HKTES2 {
+	return C.Bind(
+		mchain,
+		mmap,
+		setter,
+		F.Flow2(f, fromEither),
+	)
+}

v2/internal/fromreader/reader.go

@@ -17,6 +17,7 @@ package fromreader
 
 import (
 	F "github.com/IBM/fp-go/v2/function"
+	C "github.com/IBM/fp-go/v2/internal/chain"
 	G "github.com/IBM/fp-go/v2/reader/generic"
 )
 
@@ -69,3 +70,24 @@ func ChainFirstReaderK[GB ~func(R) B, R, A, B, HKTRA, HKTRB any](
 ) func(HKTRA) HKTRA {
 	return mchain(FromReaderK(fromReader, f))
 }
+
+//go:inline
+func BindReaderK[
+	GT ~func(R) T,
+	R, S1, S2, T,
+	HKTET,
+	HKTES1,
+	HKTES2 any](
+	mchain func(func(S1) HKTES2) func(HKTES1) HKTES2,
+	mmap func(func(T) S2) func(HKTET) HKTES2,
+	fromReader func(GT) HKTET,
+	setter func(T) func(S1) S2,
+	f func(S1) GT,
+) func(HKTES1) HKTES2 {
+	return C.Bind(
+		mchain,
+		mmap,
+		setter,
+		FromReaderK(fromReader, f),
+	)
+}

v2/readereither/bind.go

@@ -16,6 +16,7 @@
 package readereither
 
 import (
+	ET "github.com/IBM/fp-go/v2/either"
 	F "github.com/IBM/fp-go/v2/function"
 	L "github.com/IBM/fp-go/v2/optics/lens"
 	G "github.com/IBM/fp-go/v2/readereither/generic"
@@ -35,6 +36,8 @@ import (
 //	    ConfigService ConfigService
 //	}
 //	result := readereither.Do[Env, error](State{})
+//
+//go:inline
 func Do[R, E, S any](
 	empty S,
 ) ReaderEither[R, E, S] {
@@ -83,6 +86,8 @@ func Do[R, E, S any](
 //	        },
 //	    ),
 //	)
+//
+//go:inline
 func Bind[R, E, S1, S2, T any](
 	setter func(T) func(S1) S2,
 	f func(S1) ReaderEither[R, E, T],
@@ -90,7 +95,59 @@ func Bind[R, E, S1, S2, T any](
 	return G.Bind[ReaderEither[R, E, S1], ReaderEither[R, E, S2]](setter, f)
 }
 
+//go:inline
+func BindReaderK[R, E, S1, S2, T any](
+	setter func(T) func(S1) S2,
+	f func(S1) Reader[R, T],
+) func(ReaderEither[R, E, S1]) ReaderEither[R, E, S2] {
+	return G.BindReaderK[ReaderEither[R, E, S1], ReaderEither[R, E, S2]](setter, f)
+}
+
+//go:inline
+func BindEitherK[R, E, S1, S2, T any](
+	setter func(T) func(S1) S2,
+	f func(S1) Either[E, T],
+) func(ReaderEither[R, E, S1]) ReaderEither[R, E, S2] {
+	return G.BindEitherK[ReaderEither[R, E, S1], ReaderEither[R, E, S2]](setter, f)
+}
+
+//go:inline
+func BindToReader[
+	R, E, S1, T any](
+	setter func(T) S1,
+) func(Reader[R, T]) ReaderEither[R, E, S1] {
+	return G.BindToReader[ReaderEither[R, E, S1], Reader[R, T]](setter)
+}
+
+//go:inline
+func BindToEither[
+	R, E, S1, T any](
+	setter func(T) S1,
+) func(ET.Either[E, T]) ReaderEither[R, E, S1] {
+	return G.BindToEither[ReaderEither[R, E, S1]](setter)
+}
+
+//go:inline
+func ApReaderS[
+	R, E, S1, S2, T any](
+	setter func(T) func(S1) S2,
+	fa Reader[R, T],
+) Operator[R, E, S1, S2] {
+	return G.ApReaderS[ReaderEither[R, E, S1], ReaderEither[R, E, S2]](setter, fa)
+}
+
+//go:inline
+func ApEitherS[
+	R, E, S1, S2, T any](
+	setter func(T) func(S1) S2,
+	fa ET.Either[E, T],
+) Operator[R, E, S1, S2] {
+	return G.ApEitherS[ReaderEither[R, E, S1], ReaderEither[R, E, S2]](setter, fa)
+}
+
 // Let attaches the result of a computation to a context [S1] to produce a context [S2]
+//
+//go:inline
 func Let[R, E, S1, S2, T any](
 	setter func(T) func(S1) S2,
 	f func(S1) T,

v2/readereither/generic/bind.go

@@ -17,8 +17,11 @@ package generic
 
 import (
 	ET "github.com/IBM/fp-go/v2/either"
+	"github.com/IBM/fp-go/v2/function"
 	A "github.com/IBM/fp-go/v2/internal/apply"
 	C "github.com/IBM/fp-go/v2/internal/chain"
+	FE "github.com/IBM/fp-go/v2/internal/fromeither"
+	FR "github.com/IBM/fp-go/v2/internal/fromreader"
 	F "github.com/IBM/fp-go/v2/internal/functor"
 )
 
@@ -36,6 +39,8 @@ import (
 //	    UserService   UserService
 //	}
 //	result := generic.Do[ReaderEither[Env, error, State], Env, error, State](State{})
+//
+//go:inline
 func Do[GS ~func(R) ET.Either[E, S], R, E, S any](
 	empty S,
 ) GS {
@@ -84,7 +89,12 @@ func Do[GS ~func(R) ET.Either[E, S], R, E, S any](
 //	        },
 //	    ),
 //	)
-func Bind[GS1 ~func(R) ET.Either[E, S1], GS2 ~func(R) ET.Either[E, S2], GT ~func(R) ET.Either[E, T], R, E, S1, S2, T any](
+//
+//go:inline
+func Bind[
+	GS1 ~func(R) ET.Either[E, S1],
+	GS2 ~func(R) ET.Either[E, S2],
+	GT ~func(R) ET.Either[E, T], R, E, S1, S2, T any](
 	setter func(T) func(S1) S2,
 	f func(S1) GT,
 ) func(GS1) GS2 {
@@ -96,6 +106,41 @@ func Bind[GS1 ~func(R) ET.Either[E, S1], GS2 ~func(R) ET.Either[E, S2], GT ~func
 	)
 }
 
+//go:inline
+func BindReaderK[
+	GS1 ~func(R) ET.Either[E, S1],
+	GS2 ~func(R) ET.Either[E, S2],
+	GRT ~func(R) T,
+	R, E, S1, S2, T any](
+	setter func(T) func(S1) S2,
+	f func(S1) GRT,
+) func(GS1) GS2 {
+	return FR.BindReaderK(
+		Chain[GS1, GS2, E, R, S1, S2],
+		Map[func(R) ET.Either[E, T], GS2, E, R, T, S2],
+		FromReader[GRT, func(R) ET.Either[E, T]],
+		setter,
+		f,
+	)
+}
+
+//go:inline
+func BindEitherK[
+	GS1 ~func(R) ET.Either[E, S1],
+	GS2 ~func(R) ET.Either[E, S2],
+	R, E, S1, S2, T any](
+	setter func(T) func(S1) S2,
+	f func(S1) ET.Either[E, T],
+) func(GS1) GS2 {
+	return FE.BindEitherK(
+		Chain[GS1, GS2, E, R, S1, S2],
+		Map[func(R) ET.Either[E, T], GS2, E, R, T, S2],
+		FromEither[func(R) ET.Either[E, T]],
+		setter,
+		f,
+	)
+}
+
 // Let attaches the result of a computation to a context [S1] to produce a context [S2]
 func Let[GS1 ~func(R) ET.Either[E, S1], GS2 ~func(R) ET.Either[E, S2], R, E, S1, S2, T any](
 	key func(T) func(S1) S2,
@@ -130,6 +175,31 @@ func BindTo[GS1 ~func(R) ET.Either[E, S1], GT ~func(R) ET.Either[E, T], R, E, S1
 	)
 }
 
+//go:inline
+func BindToReader[
+	GS1 ~func(R) ET.Either[E, S1],
+	GT ~func(R) T,
+	R, E, S1, T any](
+	setter func(T) S1,
+) func(GT) GS1 {
+	return function.Flow2(
+		FromReader[GT, func(R) ET.Either[E, T]],
+		BindTo[GS1, func(R) ET.Either[E, T]](setter),
+	)
+}
+
+//go:inline
+func BindToEither[
+	GS1 ~func(R) ET.Either[E, S1],
+	R, E, S1, T any](
+	setter func(T) S1,
+) func(ET.Either[E, T]) GS1 {
+	return function.Flow2(
+		FromEither[func(R) ET.Either[E, T]],
+		BindTo[GS1, func(R) ET.Either[E, T]](setter),
+	)
+}
+
 // ApS attaches a value to a context [S1] to produce a context [S2] by considering
 // the context and the value concurrently (using Applicative rather than Monad).
 // This allows independent computations to be combined without one depending on the result of the other.
@@ -182,3 +252,32 @@ func ApS[GS1 ~func(R) ET.Either[E, S1], GS2 ~func(R) ET.Either[E, S2], GT ~func(
 		fa,
 	)
 }
+
+//go:inline
+func ApReaderS[
+	GS1 ~func(R) ET.Either[E, S1],
+	GS2 ~func(R) ET.Either[E, S2],
+	GT ~func(R) T,
+	R, E, S1, S2, T any](
+	setter func(T) func(S1) S2,
+	fa GT,
+) func(GS1) GS2 {
+	return ApS[GS1, GS2](
+		setter,
+		FromReader[GT, func(R) ET.Either[E, T]](fa),
+	)
+}
+
+//go:inline
+func ApEitherS[
+	GS1 ~func(R) ET.Either[E, S1],
+	GS2 ~func(R) ET.Either[E, S2],
+	R, E, S1, S2, T any](
+	setter func(T) func(S1) S2,
+	fa ET.Either[E, T],
+) func(GS1) GS2 {
+	return ApS[GS1, GS2](
+		setter,
+		FromEither[func(R) ET.Either[E, T]](fa),
+	)
+}

v2/readereither/generic/reader.go

@@ -71,6 +71,23 @@ func Chain[GEA ~func(E) ET.Either[L, A], GEB ~func(E) ET.Either[L, B], L, E, A,
 	return F.Bind2nd(MonadChain[GEA, GEB, L, E, A, B], f)
 }
 
+func MonadChainReaderK[
+	GEA ~func(E) ET.Either[L, A],
+	GEB ~func(E) ET.Either[L, B],
+	GB ~func(E) B,
+	L, E, A, B any](ma GEA, f func(A) GB) GEB {
+
+	return MonadChain(ma, F.Flow2(f, FromReader[GB, GEB, L, E, B]))
+}
+
+func ChainReaderK[
+	GEA ~func(E) ET.Either[L, A],
+	GEB ~func(E) ET.Either[L, B],
+	GB ~func(E) B,
+	L, E, A, B any](f func(A) GB) func(GEA) GEB {
+	return Chain[GEA, GEB, L, E, A, B](F.Flow2(f, FromReader[GB, GEB, L, E, B]))
+}
+
 func Of[GEA ~func(E) ET.Either[L, A], L, E, A any](a A) GEA {
 	return readert.MonadOf[GEA](ET.Of[L, A], a)
 }

v2/readerresult/bind.go

@@ -18,7 +18,9 @@ package readerresult
 import (
 	F "github.com/IBM/fp-go/v2/function"
 	L "github.com/IBM/fp-go/v2/optics/lens"
+	"github.com/IBM/fp-go/v2/reader"
 	G "github.com/IBM/fp-go/v2/readereither/generic"
+	"github.com/IBM/fp-go/v2/result"
 )
 
 // Do creates an empty context of type [S] to be used with the [Bind] operation.
@@ -321,3 +323,277 @@ func LetToL[R, S, T any](
 ) Operator[R, S, S] {
 	return LetTo[R](lens.Set, b)
 }
+
+// BindReaderK lifts a Reader Kleisli arrow into a ReaderResult context and binds it to the state.
+// This allows you to integrate pure Reader computations (that don't have error handling)
+// into a ReaderResult computation chain.
+//
+// The function f takes the current state S1 and returns a Reader[R, T] computation.
+// The result T is then attached to the state using the setter to produce state S2.
+//
+// Example:
+//
+//	type Env struct {
+//	    ConfigPath string
+//	}
+//	type State struct {
+//	    Config string
+//	}
+//
+//	// A pure Reader computation that reads from environment
+//	getConfigPath := func(s State) reader.Reader[Env, string] {
+//	    return func(env Env) string {
+//	        return env.ConfigPath
+//	    }
+//	}
+//
+//	result := F.Pipe2(
+//	    readerresult.Do[Env](State{}),
+//	    readerresult.BindReaderK(
+//	        func(path string) func(State) State {
+//	            return func(s State) State { s.Config = path; return s }
+//	        },
+//	        getConfigPath,
+//	    ),
+//	)
+//
+//go:inline
+func BindReaderK[R, S1, S2, T any](
+	setter func(T) func(S1) S2,
+	f reader.Kleisli[R, S1, T],
+) Operator[R, S1, S2] {
+	return G.BindReaderK[ReaderResult[R, S1], ReaderResult[R, S2]](setter, f)
+}
+
+//go:inline
+func BindEitherK[R, S1, S2, T any](
+	setter func(T) func(S1) S2,
+	f result.Kleisli[S1, T],
+) Operator[R, S1, S2] {
+	return G.BindEitherK[ReaderResult[R, S1], ReaderResult[R, S2]](setter, f)
+}
+
+// BindResultK lifts a Result Kleisli arrow into a ReaderResult context and binds it to the state.
+// This allows you to integrate Result computations (that may fail with an error but don't need
+// environment access) into a ReaderResult computation chain.
+//
+// The function f takes the current state S1 and returns a Result[T] computation.
+// If the Result is successful, the value T is attached to the state using the setter to produce state S2.
+// If the Result is an error, the entire computation short-circuits with that error.
+//
+// Example:
+//
+//	type State struct {
+//	    Value int
+//	    ParsedValue int
+//	}
+//
+//	// A Result computation that may fail
+//	parseValue := func(s State) result.Result[int] {
+//	    if s.Value < 0 {
+//	        return result.Error[int](errors.New("negative value"))
+//	    }
+//	    return result.Of(s.Value * 2)
+//	}
+//
+//	result := F.Pipe2(
+//	    readerresult.Do[any](State{Value: 5}),
+//	    readerresult.BindResultK(
+//	        func(parsed int) func(State) State {
+//	            return func(s State) State { s.ParsedValue = parsed; return s }
+//	        },
+//	        parseValue,
+//	    ),
+//	)
+//
+//go:inline
+func BindResultK[R, S1, S2, T any](
+	setter func(T) func(S1) S2,
+	f result.Kleisli[S1, T],
+) Operator[R, S1, S2] {
+	return G.BindEitherK[ReaderResult[R, S1], ReaderResult[R, S2]](setter, f)
+}
+
+// BindToReader initializes a new state S1 from a Reader[R, T] computation.
+// This is used to start a ReaderResult computation chain from a pure Reader value.
+//
+// The setter function takes the result T from the Reader and initializes the state S1.
+// This is useful when you want to begin a do-notation chain with a Reader computation
+// that doesn't involve error handling.
+//
+// Example:
+//
+//	type Env struct {
+//	    ConfigPath string
+//	}
+//	type State struct {
+//	    Config string
+//	}
+//
+//	// A Reader that just reads from the environment
+//	getConfigPath := func(env Env) string {
+//	    return env.ConfigPath
+//	}
+//
+//	result := F.Pipe1(
+//	    reader.Of[Env](getConfigPath),
+//	    readerresult.BindToReader(func(path string) State {
+//	        return State{Config: path}
+//	    }),
+//	)
+//
+//go:inline
+func BindToReader[
+	R, S1, T any](
+	setter func(T) S1,
+) func(Reader[R, T]) ReaderResult[R, S1] {
+	return G.BindToReader[ReaderResult[R, S1], Reader[R, T]](setter)
+}
+
+//go:inline
+func BindToEither[
+	R, S1, T any](
+	setter func(T) S1,
+) func(Result[T]) ReaderResult[R, S1] {
+	return G.BindToEither[ReaderResult[R, S1]](setter)
+}
+
+// BindToResult initializes a new state S1 from a Result[T] value.
+// This is used to start a ReaderResult computation chain from a Result that may contain an error.
+//
+// The setter function takes the successful result T and initializes the state S1.
+// If the Result is an error, the entire computation will carry that error forward.
+// This is useful when you want to begin a do-notation chain with a Result computation
+// that doesn't need environment access.
+//
+// Example:
+//
+//	type State struct {
+//	    Value int
+//	}
+//
+//	// A Result that might contain an error
+//	parseResult := result.TryCatch(func() int {
+//	    // some parsing logic that might fail
+//	    return 42
+//	})
+//
+//	computation := F.Pipe1(
+//	    parseResult,
+//	    readerresult.BindToResult[any](func(value int) State {
+//	        return State{Value: value}
+//	    }),
+//	)
+//
+//go:inline
+func BindToResult[
+	R, S1, T any](
+	setter func(T) S1,
+) func(Result[T]) ReaderResult[R, S1] {
+	return G.BindToEither[ReaderResult[R, S1]](setter)
+}
+
+// ApReaderS attaches a value from a pure Reader computation to a context [S1] to produce a context [S2]
+// using Applicative semantics (independent, non-sequential composition).
+//
+// Unlike BindReaderK which uses monadic bind (sequential), ApReaderS uses applicative apply,
+// meaning the Reader computation fa is independent of the current state and can conceptually
+// execute in parallel.
+//
+// This is useful when you want to combine a Reader computation with your ReaderResult state
+// without creating a dependency between them.
+//
+// Example:
+//
+//	type Env struct {
+//	    DefaultPort int
+//	    DefaultHost string
+//	}
+//	type State struct {
+//	    Port int
+//	    Host string
+//	}
+//
+//	getDefaultPort := func(env Env) int { return env.DefaultPort }
+//	getDefaultHost := func(env Env) string { return env.DefaultHost }
+//
+//	result := F.Pipe2(
+//	    readerresult.Do[Env](State{}),
+//	    readerresult.ApReaderS(
+//	        func(port int) func(State) State {
+//	            return func(s State) State { s.Port = port; return s }
+//	        },
+//	        getDefaultPort,
+//	    ),
+//	    readerresult.ApReaderS(
+//	        func(host string) func(State) State {
+//	            return func(s State) State { s.Host = host; return s }
+//	        },
+//	        getDefaultHost,
+//	    ),
+//	)
+//
+//go:inline
+func ApReaderS[
+	R, S1, S2, T any](
+	setter func(T) func(S1) S2,
+	fa Reader[R, T],
+) Operator[R, S1, S2] {
+	return G.ApReaderS[ReaderResult[R, S1], ReaderResult[R, S2]](setter, fa)
+}
+
+//go:inline
+func ApEitherS[
+	R, S1, S2, T any](
+	setter func(T) func(S1) S2,
+	fa Result[T],
+) Operator[R, S1, S2] {
+	return G.ApEitherS[ReaderResult[R, S1], ReaderResult[R, S2]](setter, fa)
+}
+
+// ApResultS attaches a value from a Result to a context [S1] to produce a context [S2]
+// using Applicative semantics (independent, non-sequential composition).
+//
+// Unlike BindResultK which uses monadic bind (sequential), ApResultS uses applicative apply,
+// meaning the Result computation fa is independent of the current state and can conceptually
+// execute in parallel.
+//
+// If the Result fa contains an error, the entire computation short-circuits with that error.
+// This is useful when you want to combine a Result value with your ReaderResult state
+// without creating a dependency between them.
+//
+// Example:
+//
+//	type State struct {
+//	    Value1 int
+//	    Value2 int
+//	}
+//
+//	// Independent Result computations
+//	parseValue1 := result.TryCatch(func() int { return 42 })
+//	parseValue2 := result.TryCatch(func() int { return 100 })
+//
+//	computation := F.Pipe2(
+//	    readerresult.Do[any](State{}),
+//	    readerresult.ApResultS(
+//	        func(v int) func(State) State {
+//	            return func(s State) State { s.Value1 = v; return s }
+//	        },
+//	        parseValue1,
+//	    ),
+//	    readerresult.ApResultS(
+//	        func(v int) func(State) State {
+//	            return func(s State) State { s.Value2 = v; return s }
+//	        },
+//	        parseValue2,
+//	    ),
+//	)
+//
+//go:inline
+func ApResultS[
+	R, S1, S2, T any](
+	setter func(T) func(S1) S2,
+	fa Result[T],
+) Operator[R, S1, S2] {
+	return G.ApEitherS[ReaderResult[R, S1], ReaderResult[R, S2]](setter, fa)
+}

v2/readerresult/bind_test.go

@@ -56,3 +56,291 @@ func TestApS(t *testing.T) {
 
 	assert.Equal(t, res(context.Background()), result.Of("John Doe"))
 }
+
+func TestBindReaderK(t *testing.T) {
+	type Env struct {
+		ConfigPath string
+	}
+	type State struct {
+		Config string
+	}
+
+	// A pure Reader computation
+	getConfigPath := func(s State) func(Env) string {
+		return func(env Env) string {
+			return env.ConfigPath
+		}
+	}
+
+	res := F.Pipe2(
+		Do[Env](State{}),
+		BindReaderK(
+			func(path string) func(State) State {
+				return func(s State) State {
+					s.Config = path
+					return s
+				}
+			},
+			getConfigPath,
+		),
+		Map[Env](func(s State) string { return s.Config }),
+	)
+
+	env := Env{ConfigPath: "/etc/config"}
+	assert.Equal(t, result.Of("/etc/config"), res(env))
+}
+
+func TestBindResultK(t *testing.T) {
+	type State struct {
+		Value       int
+		ParsedValue int
+	}
+
+	// A Result computation that may fail
+	parseValue := func(s State) result.Result[int] {
+		if s.Value < 0 {
+			return result.Left[int](assert.AnError)
+		}
+		return result.Of(s.Value * 2)
+	}
+
+	t.Run("success case", func(t *testing.T) {
+		res := F.Pipe2(
+			Do[context.Context](State{Value: 5}),
+			BindResultK[context.Context](
+				func(parsed int) func(State) State {
+					return func(s State) State {
+						s.ParsedValue = parsed
+						return s
+					}
+				},
+				parseValue,
+			),
+			Map[context.Context](func(s State) int { return s.ParsedValue }),
+		)
+
+		assert.Equal(t, result.Of(10), res(context.Background()))
+	})
+
+	t.Run("error case", func(t *testing.T) {
+		res := F.Pipe2(
+			Do[context.Context](State{Value: -5}),
+			BindResultK[context.Context](
+				func(parsed int) func(State) State {
+					return func(s State) State {
+						s.ParsedValue = parsed
+						return s
+					}
+				},
+				parseValue,
+			),
+			Map[context.Context](func(s State) int { return s.ParsedValue }),
+		)
+
+		assert.True(t, result.IsLeft(res(context.Background())))
+	})
+}
+
+func TestBindToReader(t *testing.T) {
+	type Env struct {
+		ConfigPath string
+	}
+	type State struct {
+		Config string
+	}
+
+	// A Reader that just reads from the environment
+	getConfigPath := func(env Env) string {
+		return env.ConfigPath
+	}
+
+	res := F.Pipe2(
+		getConfigPath,
+		BindToReader[Env](func(path string) State {
+			return State{Config: path}
+		}),
+		Map[Env](func(s State) string { return s.Config }),
+	)
+
+	env := Env{ConfigPath: "/etc/config"}
+	assert.Equal(t, result.Of("/etc/config"), res(env))
+}
+
+func TestBindToResult(t *testing.T) {
+	type State struct {
+		Value int
+	}
+
+	t.Run("success case", func(t *testing.T) {
+		parseResult := result.Of(42)
+
+		computation := F.Pipe2(
+			parseResult,
+			BindToResult[context.Context](func(value int) State {
+				return State{Value: value}
+			}),
+			Map[context.Context](func(s State) int { return s.Value }),
+		)
+
+		assert.Equal(t, result.Of(42), computation(context.Background()))
+	})
+
+	t.Run("error case", func(t *testing.T) {
+		parseResult := result.Left[int](assert.AnError)
+
+		computation := F.Pipe2(
+			parseResult,
+			BindToResult[context.Context](func(value int) State {
+				return State{Value: value}
+			}),
+			Map[context.Context](func(s State) int { return s.Value }),
+		)
+
+		assert.True(t, result.IsLeft(computation(context.Background())))
+	})
+}
+
+func TestApReaderS(t *testing.T) {
+	type Env struct {
+		DefaultPort int
+		DefaultHost string
+	}
+	type State struct {
+		Port int
+		Host string
+	}
+
+	getDefaultPort := func(env Env) int { return env.DefaultPort }
+	getDefaultHost := func(env Env) string { return env.DefaultHost }
+
+	res := F.Pipe3(
+		Do[Env](State{}),
+		ApReaderS(
+			func(port int) func(State) State {
+				return func(s State) State {
+					s.Port = port
+					return s
+				}
+			},
+			getDefaultPort,
+		),
+		ApReaderS(
+			func(host string) func(State) State {
+				return func(s State) State {
+					s.Host = host
+					return s
+				}
+			},
+			getDefaultHost,
+		),
+		Map[Env](func(s State) State { return s }),
+	)
+
+	env := Env{DefaultPort: 8080, DefaultHost: "localhost"}
+	r := res(env)
+	assert.True(t, result.IsRight(r))
+	state := result.GetOrElse(func(error) State { return State{} })(r)
+	assert.Equal(t, 8080, state.Port)
+	assert.Equal(t, "localhost", state.Host)
+}
+
+func TestApResultS(t *testing.T) {
+	type State struct {
+		Value1 int
+		Value2 int
+	}
+
+	t.Run("success case", func(t *testing.T) {
+		parseValue1 := result.Of(42)
+		parseValue2 := result.Of(100)
+
+		computation := F.Pipe3(
+			Do[context.Context](State{}),
+			ApResultS[context.Context](
+				func(v int) func(State) State {
+					return func(s State) State {
+						s.Value1 = v
+						return s
+					}
+				},
+				parseValue1,
+			),
+			ApResultS[context.Context](
+				func(v int) func(State) State {
+					return func(s State) State {
+						s.Value2 = v
+						return s
+					}
+				},
+				parseValue2,
+			),
+			Map[context.Context](func(s State) State { return s }),
+		)
+
+		r := computation(context.Background())
+		assert.True(t, result.IsRight(r))
+		state := result.GetOrElse(func(error) State { return State{} })(r)
+		assert.Equal(t, 42, state.Value1)
+		assert.Equal(t, 100, state.Value2)
+	})
+
+	t.Run("error in first value", func(t *testing.T) {
+		parseValue1 := result.Left[int](assert.AnError)
+		parseValue2 := result.Of(100)
+
+		computation := F.Pipe3(
+			Do[context.Context](State{}),
+			ApResultS[context.Context](
+				func(v int) func(State) State {
+					return func(s State) State {
+						s.Value1 = v
+						return s
+					}
+				},
+				parseValue1,
+			),
+			ApResultS[context.Context](
+				func(v int) func(State) State {
+					return func(s State) State {
+						s.Value2 = v
+						return s
+					}
+				},
+				parseValue2,
+			),
+			Map[context.Context](func(s State) State { return s }),
+		)
+
+		assert.True(t, result.IsLeft(computation(context.Background())))
+	})
+
+	t.Run("error in second value", func(t *testing.T) {
+		parseValue1 := result.Of(42)
+		parseValue2 := result.Left[int](assert.AnError)
+
+		computation := F.Pipe3(
+			Do[context.Context](State{}),
+			ApResultS[context.Context](
+				func(v int) func(State) State {
+					return func(s State) State {
+						s.Value1 = v
+						return s
+					}
+				},
+				parseValue1,
+			),
+			ApResultS[context.Context](
+				func(v int) func(State) State {
+					return func(s State) State {
+						s.Value2 = v
+						return s
+					}
+				},
+				parseValue2,
+			),
+			Map[context.Context](func(s State) State { return s }),
+		)
+
+		assert.True(t, result.IsLeft(computation(context.Background())))
+	})
+}