fix: correct sequence order of TraverseArraySeq for IO

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

io/generic/ap.go

@@ -27,16 +27,11 @@ const (
 
 // MonadApSeq implements the applicative on a single thread by first executing mab and the ma
 func MonadApSeq[GA ~func() A, GB ~func() B, GAB ~func() func(A) B, A, B any](mab GAB, ma GA) GB {
-	return MakeIO[GB](func() B {
-		return F.Pipe1(
-			ma(),
-			mab(),
-		)
-	})
+	return MonadChain(mab, F.Bind1st(MonadMap[GA, GB], ma))
 }
 
 // MonadApPar implements the applicative on two threads, the main thread executes mab and the actuall
-// apply operation and the second thred computes ma. Communication between the threads happens via a channel
+// apply operation and the second thread computes ma. Communication between the threads happens via a channel
 func MonadApPar[GA ~func() A, GB ~func() B, GAB ~func() func(A) B, A, B any](mab GAB, ma GA) GB {
 	return MakeIO[GB](func() B {
 		c := make(chan A)

io/generic/traverse.go

@@ -32,6 +32,28 @@ func MonadTraverseArray[GB ~func() B, GBS ~func() BBS, AAS ~[]A, BBS ~[]B, A, B
 	)
 }
 
+func MonadTraverseArraySeq[GB ~func() B, GBS ~func() BBS, AAS ~[]A, BBS ~[]B, A, B any](tas AAS, f func(A) GB) GBS {
+	return RA.MonadTraverse(
+		Of[GBS, BBS],
+		Map[GBS, func() func(B) BBS, BBS, func(B) BBS],
+		ApSeq[GBS, func() func(B) BBS, GB],
+
+		tas,
+		f,
+	)
+}
+
+func MonadTraverseArrayPar[GB ~func() B, GBS ~func() BBS, AAS ~[]A, BBS ~[]B, A, B any](tas AAS, f func(A) GB) GBS {
+	return RA.MonadTraverse(
+		Of[GBS, BBS],
+		Map[GBS, func() func(B) BBS, BBS, func(B) BBS],
+		ApPar[GBS, func() func(B) BBS, GB],
+
+		tas,
+		f,
+	)
+}
+
 func TraverseArray[GB ~func() B, GBS ~func() BBS, AAS ~[]A, BBS ~[]B, A, B any](f func(A) GB) func(AAS) GBS {
 	return RA.Traverse[AAS](
 		Of[GBS, BBS],
@@ -42,6 +64,26 @@ func TraverseArray[GB ~func() B, GBS ~func() BBS, AAS ~[]A, BBS ~[]B, A, B any](
 	)
 }
 
+func TraverseArraySeq[GB ~func() B, GBS ~func() BBS, AAS ~[]A, BBS ~[]B, A, B any](f func(A) GB) func(AAS) GBS {
+	return RA.Traverse[AAS](
+		Of[GBS, BBS],
+		Map[GBS, func() func(B) BBS, BBS, func(B) BBS],
+		ApSeq[GBS, func() func(B) BBS, GB],
+
+		f,
+	)
+}
+
+func TraverseArrayPar[GB ~func() B, GBS ~func() BBS, AAS ~[]A, BBS ~[]B, A, B any](f func(A) GB) func(AAS) GBS {
+	return RA.Traverse[AAS](
+		Of[GBS, BBS],
+		Map[GBS, func() func(B) BBS, BBS, func(B) BBS],
+		ApPar[GBS, func() func(B) BBS, GB],
+
+		f,
+	)
+}
+
 func TraverseArrayWithIndex[GB ~func() B, GBS ~func() BBS, AAS ~[]A, BBS ~[]B, A, B any](f func(int, A) GB) func(AAS) GBS {
 	return RA.TraverseWithIndex[AAS](
 		Of[GBS, BBS],
@@ -52,10 +94,38 @@ func TraverseArrayWithIndex[GB ~func() B, GBS ~func() BBS, AAS ~[]A, BBS ~[]B, A
 	)
 }
 
+func TraverseArrayWithIndexSeq[GB ~func() B, GBS ~func() BBS, AAS ~[]A, BBS ~[]B, A, B any](f func(int, A) GB) func(AAS) GBS {
+	return RA.TraverseWithIndex[AAS](
+		Of[GBS, BBS],
+		Map[GBS, func() func(B) BBS, BBS, func(B) BBS],
+		ApSeq[GBS, func() func(B) BBS, GB],
+
+		f,
+	)
+}
+
+func TraverseArrayWithIndexPar[GB ~func() B, GBS ~func() BBS, AAS ~[]A, BBS ~[]B, A, B any](f func(int, A) GB) func(AAS) GBS {
+	return RA.TraverseWithIndex[AAS](
+		Of[GBS, BBS],
+		Map[GBS, func() func(B) BBS, BBS, func(B) BBS],
+		ApPar[GBS, func() func(B) BBS, GB],
+
+		f,
+	)
+}
+
 func SequenceArray[GA ~func() A, GAS ~func() AAS, AAS ~[]A, GAAS ~[]GA, A any](tas GAAS) GAS {
 	return MonadTraverseArray[GA, GAS](tas, F.Identity[GA])
 }
 
+func SequenceArraySeq[GA ~func() A, GAS ~func() AAS, AAS ~[]A, GAAS ~[]GA, A any](tas GAAS) GAS {
+	return MonadTraverseArraySeq[GA, GAS](tas, F.Identity[GA])
+}
+
+func SequenceArrayPar[GA ~func() A, GAS ~func() AAS, AAS ~[]A, GAAS ~[]GA, A any](tas GAAS) GAS {
+	return MonadTraverseArrayPar[GA, GAS](tas, F.Identity[GA])
+}
+
 // MonadTraverseRecord transforms a record using an IO transform an IO of a record
 func MonadTraverseRecord[GBS ~func() MB, MA ~map[K]A, GB ~func() B, MB ~map[K]B, K comparable, A, B any](ma MA, f func(A) GB) GBS {
 	return RR.MonadTraverse[MA](
@@ -89,3 +159,71 @@ func TraverseRecordWithIndex[GB ~func() B, GBS ~func() MB, MA ~map[K]A, MB ~map[
 func SequenceRecord[GA ~func() A, GAS ~func() AAS, AAS ~map[K]A, GAAS ~map[K]GA, K comparable, A any](tas GAAS) GAS {
 	return MonadTraverseRecord[GAS](tas, F.Identity[GA])
 }
+
+// MonadTraverseRecordSeq transforms a record using an IO transform an IO of a record
+func MonadTraverseRecordSeq[GBS ~func() MB, MA ~map[K]A, GB ~func() B, MB ~map[K]B, K comparable, A, B any](ma MA, f func(A) GB) GBS {
+	return RR.MonadTraverse[MA](
+		Of[GBS, MB],
+		Map[GBS, func() func(B) MB, MB, func(B) MB],
+		ApSeq[GBS, func() func(B) MB, GB],
+		ma, f,
+	)
+}
+
+// TraverseRecordSeq transforms a record using an IO transform an IO of a record
+func TraverseRecordSeq[GBS ~func() MB, MA ~map[K]A, GB ~func() B, MB ~map[K]B, K comparable, A, B any](f func(A) GB) func(MA) GBS {
+	return RR.Traverse[MA](
+		Of[GBS, MB],
+		Map[GBS, func() func(B) MB, MB, func(B) MB],
+		ApSeq[GBS, func() func(B) MB, GB],
+		f,
+	)
+}
+
+// TraverseRecordWithIndexSeq transforms a record using an IO transform an IO of a record
+func TraverseRecordWithIndexSeq[GB ~func() B, GBS ~func() MB, MA ~map[K]A, MB ~map[K]B, K comparable, A, B any](f func(K, A) GB) func(MA) GBS {
+	return RR.TraverseWithIndex[MA](
+		Of[GBS, MB],
+		Map[GBS, func() func(B) MB, MB, func(B) MB],
+		ApSeq[GBS, func() func(B) MB, GB],
+		f,
+	)
+}
+
+func SequenceRecordSeq[GA ~func() A, GAS ~func() AAS, AAS ~map[K]A, GAAS ~map[K]GA, K comparable, A any](tas GAAS) GAS {
+	return MonadTraverseRecordSeq[GAS](tas, F.Identity[GA])
+}
+
+// MonadTraverseRecordPar transforms a record using an IO transform an IO of a record
+func MonadTraverseRecordPar[GBS ~func() MB, MA ~map[K]A, GB ~func() B, MB ~map[K]B, K comparable, A, B any](ma MA, f func(A) GB) GBS {
+	return RR.MonadTraverse[MA](
+		Of[GBS, MB],
+		Map[GBS, func() func(B) MB, MB, func(B) MB],
+		ApPar[GBS, func() func(B) MB, GB],
+		ma, f,
+	)
+}
+
+// TraverseRecordPar transforms a record using an IO transform an IO of a record
+func TraverseRecordPar[GBS ~func() MB, MA ~map[K]A, GB ~func() B, MB ~map[K]B, K comparable, A, B any](f func(A) GB) func(MA) GBS {
+	return RR.Traverse[MA](
+		Of[GBS, MB],
+		Map[GBS, func() func(B) MB, MB, func(B) MB],
+		ApPar[GBS, func() func(B) MB, GB],
+		f,
+	)
+}
+
+// TraverseRecordWithIndexPar transforms a record using an IO transform an IO of a record
+func TraverseRecordWithIndexPar[GB ~func() B, GBS ~func() MB, MA ~map[K]A, MB ~map[K]B, K comparable, A, B any](f func(K, A) GB) func(MA) GBS {
+	return RR.TraverseWithIndex[MA](
+		Of[GBS, MB],
+		Map[GBS, func() func(B) MB, MB, func(B) MB],
+		ApPar[GBS, func() func(B) MB, GB],
+		f,
+	)
+}
+
+func SequenceRecordPar[GA ~func() A, GAS ~func() AAS, AAS ~map[K]A, GAAS ~map[K]GA, K comparable, A any](tas GAAS) GAS {
+	return MonadTraverseRecordPar[GAS](tas, F.Identity[GA])
+}

io/sequence_test.go

@@ -0,0 +1,47 @@
+// Copyright (c) 2023 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 io
+
+import (
+	A "github.com/IBM/fp-go/array"
+	F "github.com/IBM/fp-go/function"
+	"github.com/stretchr/testify/assert"
+
+	"testing"
+)
+
+func TestMapSeq(t *testing.T) {
+	var results []string
+
+	handler := func(value string) IO[string] {
+		return func() string {
+			results = append(results, value)
+			return value
+		}
+	}
+
+	src := A.From("a", "b", "c")
+
+	res := F.Pipe2(
+		src,
+		TraverseArraySeq(handler),
+		Map(func(data []string) bool {
+			return assert.Equal(t, data, results)
+		}),
+	)
+
+	assert.True(t, res())
+}

io/traverse.go

@@ -60,3 +60,45 @@ func TraverseRecordWithIndex[K comparable, A, B any](f func(K, A) IO[B]) func(ma
 func SequenceRecord[K comparable, A any](tas map[K]IO[A]) IO[map[K]A] {
 	return G.SequenceRecord[IO[A], IO[map[K]A]](tas)
 }
+
+func MonadTraverseArraySeq[A, B any](tas []A, f func(A) IO[B]) IO[[]B] {
+	return G.MonadTraverseArraySeq[IO[B], IO[[]B]](tas, f)
+}
+
+// TraverseArraySeq applies a function returning an [IO] to all elements in an array and the
+// transforms this into an [IO] of that array
+func TraverseArraySeq[A, B any](f func(A) IO[B]) func([]A) IO[[]B] {
+	return G.TraverseArraySeq[IO[B], IO[[]B], []A](f)
+}
+
+// TraverseArrayWithIndexSeq applies a function returning an [IO] to all elements in an array and the
+// transforms this into an [IO] of that array
+func TraverseArrayWithIndexSeq[A, B any](f func(int, A) IO[B]) func([]A) IO[[]B] {
+	return G.TraverseArrayWithIndexSeq[IO[B], IO[[]B], []A](f)
+}
+
+// SequenceArraySeq converts an array of [IO] to an [IO] of an array
+func SequenceArraySeq[A any](tas []IO[A]) IO[[]A] {
+	return G.SequenceArraySeq[IO[A], IO[[]A]](tas)
+}
+
+func MonadTraverseRecordSeq[K comparable, A, B any](tas map[K]A, f func(A) IO[B]) IO[map[K]B] {
+	return G.MonadTraverseRecordSeq[IO[map[K]B]](tas, f)
+}
+
+// TraverseRecord applies a function returning an [IO] to all elements in a record and the
+// transforms this into an [IO] of that record
+func TraverseRecordSeq[K comparable, A, B any](f func(A) IO[B]) func(map[K]A) IO[map[K]B] {
+	return G.TraverseRecordSeq[IO[map[K]B], map[K]A, IO[B]](f)
+}
+
+// TraverseRecordWithIndexSeq applies a function returning an [IO] to all elements in a record and the
+// transforms this into an [IO] of that record
+func TraverseRecordWithIndeSeq[K comparable, A, B any](f func(K, A) IO[B]) func(map[K]A) IO[map[K]B] {
+	return G.TraverseRecordWithIndexSeq[IO[B], IO[map[K]B], map[K]A](f)
+}
+
+// SequenceRecordSeq converts a record of [IO] to an [IO] of a record
+func SequenceRecordSeq[K comparable, A any](tas map[K]IO[A]) IO[map[K]A] {
+	return G.SequenceRecordSeq[IO[A], IO[map[K]A]](tas)
+}

ioeither/sequence_test.go

@@ -0,0 +1,48 @@
+// Copyright (c) 2023 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 ioeither
+
+import (
+	A "github.com/IBM/fp-go/array"
+	E "github.com/IBM/fp-go/either"
+	F "github.com/IBM/fp-go/function"
+	"github.com/stretchr/testify/assert"
+
+	"testing"
+)
+
+func TestMapSeq(t *testing.T) {
+	var results []string
+
+	handler := func(value string) IOEither[error, string] {
+		return func() E.Either[error, string] {
+			results = append(results, value)
+			return E.Of[error](value)
+		}
+	}
+
+	src := A.From("a", "b", "c")
+
+	res := F.Pipe2(
+		src,
+		TraverseArraySeq(handler),
+		Map[error](func(data []string) bool {
+			return assert.Equal(t, data, results)
+		}),
+	)
+
+	assert.Equal(t, E.Of[error](true), res())
+}

scan.bat

@@ -0,0 +1,3 @@
+@echo off
+
+busybox find . -type f -name "*\.go" | busybox xargs gopls check

state/eq.go

@@ -0,0 +1,31 @@
+// Copyright (c) 2023 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 state
+
+import (
+	EQ "github.com/IBM/fp-go/eq"
+	G "github.com/IBM/fp-go/state/generic"
+)
+
+// Constructs an equal predicate for a [State]
+func Eq[S, A any](w EQ.Eq[S], a EQ.Eq[A]) func(S) EQ.Eq[State[S, A]] {
+	return G.Eq[State[S, A]](w, a)
+}
+
+// FromStrictEquals constructs an [EQ.Eq] from the canonical comparison function
+func FromStrictEquals[S, A comparable]() func(S) EQ.Eq[State[S, A]] {
+	return G.FromStrictEquals[State[S, A]]()
+}

state/generic/eq.go

@@ -0,0 +1,36 @@
+// Copyright (c) 2023 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 generic
+
+import (
+	EQ "github.com/IBM/fp-go/eq"
+	P "github.com/IBM/fp-go/pair"
+)
+
+// Constructs an equal predicate for a [State]
+func Eq[GA ~func(S) P.Pair[A, S], S, A any](w EQ.Eq[S], a EQ.Eq[A]) func(S) EQ.Eq[GA] {
+	eqp := P.Eq(a, w)
+	return func(s S) EQ.Eq[GA] {
+		return EQ.FromEquals(func(l, r GA) bool {
+			return eqp.Equals(l(s), r(s))
+		})
+	}
+}
+
+// FromStrictEquals constructs an [EQ.Eq] from the canonical comparison function
+func FromStrictEquals[GA ~func(S) P.Pair[A, S], S, A comparable]() func(S) EQ.Eq[GA] {
+	return Eq[GA](EQ.FromStrictEquals[S](), EQ.FromStrictEquals[A]())
+}

state/generic/monad.go

@@ -0,0 +1,88 @@
+// Copyright (c) 2024 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 generic
+
+import (
+	"github.com/IBM/fp-go/internal/applicative"
+	"github.com/IBM/fp-go/internal/functor"
+	"github.com/IBM/fp-go/internal/monad"
+	"github.com/IBM/fp-go/internal/pointed"
+	P "github.com/IBM/fp-go/pair"
+)
+
+type statePointed[GA ~func(S) P.Pair[A, S], S, A any] struct{}
+
+type stateFunctor[GB ~func(S) P.Pair[B, S], GA ~func(S) P.Pair[A, S], S, A, B any] struct{}
+
+type stateApplicative[GB ~func(S) P.Pair[B, S], GAB ~func(S) P.Pair[func(A) B, S], GA ~func(S) P.Pair[A, S], S, A, B any] struct{}
+
+type stateMonad[GB ~func(S) P.Pair[B, S], GAB ~func(S) P.Pair[func(A) B, S], GA ~func(S) P.Pair[A, S], S, A, B any] struct{}
+
+func (o *statePointed[GA, S, A]) Of(a A) GA {
+	return Of[GA](a)
+}
+
+func (o *stateApplicative[GB, GAB, GA, S, A, B]) Of(a A) GA {
+	return Of[GA](a)
+}
+
+func (o *stateMonad[GB, GAB, GA, S, A, B]) Of(a A) GA {
+	return Of[GA](a)
+}
+
+func (o *stateFunctor[GB, GA, S, A, B]) Map(f func(A) B) func(GA) GB {
+	return Map[GB, GA](f)
+}
+
+func (o *stateApplicative[GB, GAB, GA, S, A, B]) Map(f func(A) B) func(GA) GB {
+	return Map[GB, GA](f)
+}
+
+func (o *stateMonad[GB, GAB, GA, S, A, B]) Map(f func(A) B) func(GA) GB {
+	return Map[GB, GA](f)
+}
+
+func (o *stateMonad[GB, GAB, GA, S, A, B]) Chain(f func(A) GB) func(GA) GB {
+	return Chain[GB, GA](f)
+}
+
+func (o *stateApplicative[GB, GAB, GA, S, A, B]) Ap(fa GA) func(GAB) GB {
+	return Ap[GB, GAB, GA](fa)
+}
+
+func (o *stateMonad[GB, GAB, GA, S, A, B]) Ap(fa GA) func(GAB) GB {
+	return Ap[GB, GAB, GA](fa)
+}
+
+// Pointed implements the pointed operations for [Writer]
+func Pointed[GA ~func(S) P.Pair[A, S], S, A any]() pointed.Pointed[A, GA] {
+	return &statePointed[GA, S, A]{}
+}
+
+// Functor implements the functor operations for [Writer]
+func Functor[GB ~func(S) P.Pair[B, S], GA ~func(S) P.Pair[A, S], S, A, B any]() functor.Functor[A, B, GA, GB] {
+	return &stateFunctor[GB, GA, S, A, B]{}
+}
+
+// Applicative implements the applicative operations for [Writer]
+func Applicative[GB ~func(S) P.Pair[B, S], GAB ~func(S) P.Pair[func(A) B, S], GA ~func(S) P.Pair[A, S], S, A, B any]() applicative.Applicative[A, B, GA, GB, GAB] {
+	return &stateApplicative[GB, GAB, GA, S, A, B]{}
+}
+
+// Monad implements the monadic operations for [Writer]
+func Monad[GB ~func(S) P.Pair[B, S], GAB ~func(S) P.Pair[func(A) B, S], GA ~func(S) P.Pair[A, S], S, A, B any]() monad.Monad[A, B, GA, GB, GAB] {
+	return &stateMonad[GB, GAB, GA, S, A, B]{}
+}

state/generic/state.go

@@ -0,0 +1,131 @@
+// Copyright (c) 2024 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 generic
+
+import (
+	F "github.com/IBM/fp-go/function"
+	C "github.com/IBM/fp-go/internal/chain"
+	FC "github.com/IBM/fp-go/internal/functor"
+	P "github.com/IBM/fp-go/pair"
+)
+
+var (
+	undefined any = struct{}{}
+)
+
+func Get[GA ~func(S) P.Pair[S, S], S any]() GA {
+	return P.Of[S]
+}
+
+func Gets[GA ~func(S) P.Pair[A, S], FCT ~func(S) A, A, S any](f FCT) GA {
+	return func(s S) P.Pair[A, S] {
+		return P.MakePair(f(s), s)
+	}
+}
+
+func Put[GA ~func(S) P.Pair[any, S], S any]() GA {
+	return F.Bind1st(P.MakePair[any, S], undefined)
+}
+
+func Modify[GA ~func(S) P.Pair[any, S], FCT ~func(S) S, S any](f FCT) GA {
+	return F.Flow2(
+		f,
+		F.Bind1st(P.MakePair[any, S], undefined),
+	)
+}
+
+func Of[GA ~func(S) P.Pair[A, S], S, A any](a A) GA {
+	return F.Bind1st(P.MakePair[A, S], a)
+}
+
+func MonadMap[GB ~func(S) P.Pair[B, S], GA ~func(S) P.Pair[A, S], FCT ~func(A) B, S, A, B any](fa GA, f FCT) GB {
+	return func(s S) P.Pair[B, S] {
+		p2 := fa(s)
+		return P.MakePair(f(P.Head(p2)), P.Tail(p2))
+	}
+}
+
+func Map[GB ~func(S) P.Pair[B, S], GA ~func(S) P.Pair[A, S], FCT ~func(A) B, S, A, B any](f FCT) func(GA) GB {
+	return F.Bind2nd(MonadMap[GB, GA, FCT, S, A, B], f)
+}
+
+func MonadChain[GB ~func(S) P.Pair[B, S], GA ~func(S) P.Pair[A, S], FCT ~func(A) GB, S, A, B any](fa GA, f FCT) GB {
+	return func(s S) P.Pair[B, S] {
+		a := fa(s)
+		return f(P.Head(a))(P.Tail(a))
+	}
+}
+
+func Chain[GB ~func(S) P.Pair[B, S], GA ~func(S) P.Pair[A, S], FCT ~func(A) GB, S, A, B any](f FCT) func(GA) GB {
+	return F.Bind2nd(MonadChain[GB, GA, FCT, S, A, B], f)
+}
+
+func MonadAp[GB ~func(S) P.Pair[B, S], GAB ~func(S) P.Pair[func(A) B, S], GA ~func(S) P.Pair[A, S], S, A, B any](fab GAB, fa GA) GB {
+	return func(s S) P.Pair[B, S] {
+		f := fab(s)
+		a := fa(P.Tail(f))
+
+		return P.MakePair(P.Head(f)(P.Head(a)), P.Tail(a))
+	}
+}
+
+func Ap[GB ~func(S) P.Pair[B, S], GAB ~func(S) P.Pair[func(A) B, S], GA ~func(S) P.Pair[A, S], S, A, B any](ga GA) func(GAB) GB {
+	return F.Bind2nd(MonadAp[GB, GAB, GA, S, A, B], ga)
+}
+
+func MonadChainFirst[GB ~func(S) P.Pair[B, S], GA ~func(S) P.Pair[A, S], FCT ~func(A) GB, S, A, B any](ma GA, f FCT) GA {
+	return C.MonadChainFirst(
+		MonadChain[GA, GA, func(A) GA],
+		MonadMap[GA, GB, func(B) A],
+		ma,
+		f,
+	)
+}
+
+func ChainFirst[GB ~func(S) P.Pair[B, S], GA ~func(S) P.Pair[A, S], FCT ~func(A) GB, S, A, B any](f FCT) func(GA) GA {
+	return C.ChainFirst(
+		Chain[GA, GA, func(A) GA],
+		Map[GA, GB, func(B) A],
+		f,
+	)
+}
+
+func Flatten[GAA ~func(S) P.Pair[GA, S], GA ~func(S) P.Pair[A, S], S, A any](mma GAA) GA {
+	return MonadChain[GA, GAA, func(GA) GA](mma, F.Identity[GA])
+}
+
+func Execute[GA ~func(S) P.Pair[A, S], S, A any](s S) func(GA) S {
+	return func(fa GA) S {
+		return P.Tail(fa(s))
+	}
+}
+
+func Evaluate[GA ~func(S) P.Pair[A, S], S, A any](s S) func(GA) A {
+	return func(fa GA) A {
+		return P.Head(fa(s))
+	}
+}
+
+func MonadFlap[FAB ~func(A) B, GFAB ~func(S) P.Pair[FAB, S], GB ~func(S) P.Pair[B, S], S, A, B any](fab GFAB, a A) GB {
+	return FC.MonadFlap(
+		MonadMap[GB, GFAB, func(FAB) B],
+		fab,
+		a)
+}
+
+func Flap[FAB ~func(A) B, GFAB ~func(S) P.Pair[FAB, S], GB ~func(S) P.Pair[B, S], S, A, B any](a A) func(GFAB) GB {
+	return FC.Flap(Map[GB, GFAB, func(FAB) B], a)
+}

state/monad.go

@@ -0,0 +1,44 @@
+// Copyright (c) 2024 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 state
+
+import (
+	"github.com/IBM/fp-go/internal/applicative"
+	"github.com/IBM/fp-go/internal/functor"
+	"github.com/IBM/fp-go/internal/monad"
+	"github.com/IBM/fp-go/internal/pointed"
+	G "github.com/IBM/fp-go/state/generic"
+)
+
+// Pointed implements the pointed operations for [State]
+func Pointed[S, A any]() pointed.Pointed[A, State[S, A]] {
+	return G.Pointed[State[S, A], S, A]()
+}
+
+// Functor implements the pointed operations for [State]
+func Functor[S, A, B any]() functor.Functor[A, B, State[S, A], State[S, B]] {
+	return G.Functor[State[S, B], State[S, A], S, A, B]()
+}
+
+// Applicative implements the applicative operations for [State]
+func Applicative[S, A, B any]() applicative.Applicative[A, B, State[S, A], State[S, B], State[S, func(A) B]] {
+	return G.Applicative[State[S, B], State[S, func(A) B], State[S, A]]()
+}
+
+// Monad implements the monadic operations for [State]
+func Monad[S, A, B any]() monad.Monad[A, B, State[S, A], State[S, B], State[S, func(A) B]] {
+	return G.Monad[State[S, B], State[S, func(A) B], State[S, A]]()
+}

state/state.go

@@ -0,0 +1,97 @@
+// Copyright (c) 2024 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 state
+
+import (
+	P "github.com/IBM/fp-go/pair"
+	R "github.com/IBM/fp-go/reader"
+	G "github.com/IBM/fp-go/state/generic"
+)
+
+// State represents an operation on top of a current [State] that produces a value and a new [State]
+type State[S, A any] R.Reader[S, P.Pair[A, S]]
+
+func Get[S any]() State[S, S] {
+	return G.Get[State[S, S]]()
+}
+
+func Gets[FCT ~func(S) A, A, S any](f FCT) State[S, A] {
+	return G.Gets[State[S, A]](f)
+}
+
+func Put[S any]() State[S, any] {
+	return G.Put[State[S, any]]()
+}
+
+func Modify[FCT ~func(S) S, S any](f FCT) State[S, any] {
+	return G.Modify[State[S, any]](f)
+}
+
+func Of[S, A any](a A) State[S, A] {
+	return G.Of[State[S, A]](a)
+}
+
+func MonadMap[S any, FCT ~func(A) B, A, B any](fa State[S, A], f FCT) State[S, B] {
+	return G.MonadMap[State[S, B], State[S, A]](fa, f)
+}
+
+func Map[S any, FCT ~func(A) B, A, B any](f FCT) func(State[S, A]) State[S, B] {
+	return G.Map[State[S, B], State[S, A]](f)
+}
+
+func MonadChain[S any, FCT ~func(A) State[S, B], A, B any](fa State[S, A], f FCT) State[S, B] {
+	return G.MonadChain[State[S, B], State[S, A]](fa, f)
+}
+
+func Chain[S any, FCT ~func(A) State[S, B], A, B any](f FCT) func(State[S, A]) State[S, B] {
+	return G.Chain[State[S, B], State[S, A]](f)
+}
+
+func MonadAp[S, A, B any](fab State[S, func(A) B], fa State[S, A]) State[S, B] {
+	return G.MonadAp[State[S, B], State[S, func(A) B], State[S, A]](fab, fa)
+}
+
+func Ap[S, A, B any](ga State[S, A]) func(State[S, func(A) B]) State[S, B] {
+	return G.Ap[State[S, B], State[S, func(A) B], State[S, A]](ga)
+}
+
+func MonadChainFirst[S any, FCT ~func(A) State[S, B], A, B any](ma State[S, A], f FCT) State[S, A] {
+	return G.MonadChainFirst[State[S, B], State[S, A]](ma, f)
+}
+
+func ChainFirst[S any, FCT ~func(A) State[S, B], A, B any](f FCT) func(State[S, A]) State[S, A] {
+	return G.ChainFirst[State[S, B], State[S, A]](f)
+}
+
+func Flatten[S, A any](mma State[S, State[S, A]]) State[S, A] {
+	return G.Flatten[State[S, State[S, A]], State[S, A]](mma)
+}
+
+func Execute[A, S any](s S) func(State[S, A]) S {
+	return G.Execute[State[S, A]](s)
+}
+
+func Evaluate[A, S any](s S) func(State[S, A]) A {
+	return G.Evaluate[State[S, A]](s)
+}
+
+func MonadFlap[FAB ~func(A) B, S, A, B any](fab State[S, FAB], a A) State[S, B] {
+	return G.MonadFlap[FAB, State[S, FAB], State[S, B], S, A, B](fab, a)
+}
+
+func Flap[S, A, B any](a A) func(State[S, func(A) B]) State[S, B] {
+	return G.Flap[func(A) B, State[S, func(A) B], State[S, B]](a)
+}

state/testing/laws.go

@@ -0,0 +1,78 @@
+// Copyright (c) 2023 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 testing
+
+import (
+	"testing"
+
+	EQ "github.com/IBM/fp-go/eq"
+	L "github.com/IBM/fp-go/internal/monad/testing"
+	ST "github.com/IBM/fp-go/state"
+)
+
+// AssertLaws asserts the apply monad laws for the `Either` monad
+func AssertLaws[S, A, B, C any](t *testing.T,
+	eqw EQ.Eq[S],
+	eqa EQ.Eq[A],
+	eqb EQ.Eq[B],
+	eqc EQ.Eq[C],
+
+	ab func(A) B,
+	bc func(B) C,
+
+	s S,
+) func(a A) bool {
+
+	fofc := ST.Pointed[S, C]()
+	fofaa := ST.Pointed[S, func(A) A]()
+	fofbc := ST.Pointed[S, func(B) C]()
+	fofabb := ST.Pointed[S, func(func(A) B) B]()
+
+	fmap := ST.Functor[S, func(B) C, func(func(A) B) func(A) C]()
+
+	fapabb := ST.Applicative[S, func(A) B, B]()
+	fapabac := ST.Applicative[S, func(A) B, func(A) C]()
+
+	maa := ST.Monad[S, A, A]()
+	mab := ST.Monad[S, A, B]()
+	mac := ST.Monad[S, A, C]()
+	mbc := ST.Monad[S, B, C]()
+
+	return L.MonadAssertLaws(t,
+		ST.Eq(eqw, eqa)(s),
+		ST.Eq(eqw, eqb)(s),
+		ST.Eq(eqw, eqc)(s),
+
+		fofc,
+		fofaa,
+		fofbc,
+		fofabb,
+
+		fmap,
+
+		fapabb,
+		fapabac,
+
+		maa,
+		mab,
+		mac,
+		mbc,
+
+		ab,
+		bc,
+	)
+
+}

state/testing/laws_test.go

@@ -0,0 +1,49 @@
+// Copyright (c) 2023 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 testing
+
+import (
+	"fmt"
+	"testing"
+
+	A "github.com/IBM/fp-go/array"
+	EQ "github.com/IBM/fp-go/eq"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestMonadLaws(t *testing.T) {
+	// some comparison
+	eqs := A.Eq[string](EQ.FromStrictEquals[string]())
+	eqa := EQ.FromStrictEquals[bool]()
+	eqb := EQ.FromStrictEquals[int]()
+	eqc := EQ.FromStrictEquals[string]()
+
+	ab := func(a bool) int {
+		if a {
+			return 1
+		}
+		return 0
+	}
+
+	bc := func(b int) string {
+		return fmt.Sprintf("value %d", b)
+	}
+
+	laws := AssertLaws(t, eqs, eqa, eqb, eqc, ab, bc, A.Empty[string]())
+
+	assert.True(t, laws(true))
+	assert.True(t, laws(false))
+}

writer/bind.go

@@ -17,20 +17,22 @@ package writer
 
 import (
 	M "github.com/IBM/fp-go/monoid"
+	SG "github.com/IBM/fp-go/semigroup"
 	G "github.com/IBM/fp-go/writer/generic"
 )
 
 // Bind creates an empty context of type [S] to be used with the [Bind] operation
-func Do[S, W any](m M.Monoid[W]) func(S) Writer[W, S] {
-	return G.Do[Writer[W, S], W, S](m)
+func Do[S, W any](m M.Monoid[W], s S) Writer[W, S] {
+	return G.Do[Writer[W, S], W, S](m, s)
 }
 
 // Bind attaches the result of a computation to a context [S1] to produce a context [S2]
 func Bind[S1, S2, T, W any](
+	s SG.Semigroup[W],
 	setter func(T) func(S1) S2,
 	f func(S1) Writer[W, T],
 ) func(Writer[W, S1]) Writer[W, S2] {
-	return G.Bind[Writer[W, S1], Writer[W, S2], Writer[W, T], W, S1, S2, T](setter, f)
+	return G.Bind[Writer[W, S1], Writer[W, S2], Writer[W, T], W, S1, S2, T](s, setter, f)
 }
 
 // Let attaches the result of a computation to a context [S1] to produce a context [S2]
@@ -58,8 +60,9 @@ func BindTo[W, S1, T any](
 
 // ApS attaches a value to a context [S1] to produce a context [S2] by considering the context and the value concurrently
 func ApS[S1, S2, T, W any](
+	s SG.Semigroup[W],
 	setter func(T) func(S1) S2,
 	fa Writer[W, T],
 ) func(Writer[W, S1]) Writer[W, S2] {
-	return G.ApS[Writer[W, S1], Writer[W, S2], Writer[W, T], W, S1, S2, T](setter, fa)
+	return G.ApS[Writer[W, S1], Writer[W, S2], Writer[W, T], W, S1, S2, T](s, setter, fa)
 }

writer/bind_test.go

@@ -34,33 +34,33 @@ var (
 )
 
 func getLastName(s utils.Initial) Writer[[]string, string] {
-	return Of[string](monoid)("Doe")
+	return Of[string](monoid, "Doe")
 }
 
 func getGivenName(s utils.WithLastName) Writer[[]string, string] {
-	return Of[string](monoid)("John")
+	return Of[string](monoid, "John")
 }
 
 func TestBind(t *testing.T) {
 
 	res := F.Pipe3(
-		Do[utils.Initial](monoid)(utils.Empty),
-		Bind(utils.SetLastName, getLastName),
-		Bind(utils.SetGivenName, getGivenName),
+		Do[utils.Initial](monoid, utils.Empty),
+		Bind(sg, utils.SetLastName, getLastName),
+		Bind(sg, utils.SetGivenName, getGivenName),
 		Map[[]string](utils.GetFullName),
 	)
 
-	assert.True(t, eq.Equals(res, Of[string](monoid)("John Doe")))
+	assert.True(t, eq.Equals(res, Of[string](monoid, "John Doe")))
 }
 
 func TestApS(t *testing.T) {
 
 	res := F.Pipe3(
-		Do[utils.Initial](monoid)(utils.Empty),
-		ApS(utils.SetLastName, Of[string](monoid)("Doe")),
-		ApS(utils.SetGivenName, Of[string](monoid)("John")),
+		Do[utils.Initial](monoid, utils.Empty),
+		ApS(sg, utils.SetLastName, Of[string](monoid, "Doe")),
+		ApS(sg, utils.SetGivenName, Of[string](monoid, "John")),
 		Map[[]string](utils.GetFullName),
 	)
 
-	assert.True(t, eq.Equals(res, Of[string](monoid)("John Doe")))
+	assert.True(t, eq.Equals(res, Of[string](monoid, "John Doe")))
 }

writer/generic/bind.go

@@ -16,26 +16,28 @@
 package generic
 
 import (
+	FCT "github.com/IBM/fp-go/function"
 	"github.com/IBM/fp-go/internal/apply"
 	C "github.com/IBM/fp-go/internal/chain"
 	F "github.com/IBM/fp-go/internal/functor"
 	M "github.com/IBM/fp-go/monoid"
+	P "github.com/IBM/fp-go/pair"
 	SG "github.com/IBM/fp-go/semigroup"
-	T "github.com/IBM/fp-go/tuple"
 )
 
 // Bind creates an empty context of type [S] to be used with the [Bind] operation
-func Do[GS ~func() T.Tuple3[S, W, SG.Semigroup[W]], W, S any](m M.Monoid[W]) func(S) GS {
-	return Of[GS, W, S](m)
+func Do[GS ~func() P.Pair[S, W], W, S any](m M.Monoid[W], s S) GS {
+	return Of[GS, W, S](m, s)
 }
 
 // Bind attaches the result of a computation to a context [S1] to produce a context [S2]
-func Bind[GS1 ~func() T.Tuple3[S1, W, SG.Semigroup[W]], GS2 ~func() T.Tuple3[S2, W, SG.Semigroup[W]], GT ~func() T.Tuple3[A, W, SG.Semigroup[W]], W, S1, S2, A any](
+func Bind[GS1 ~func() P.Pair[S1, W], GS2 ~func() P.Pair[S2, W], GT ~func() P.Pair[A, W], W, S1, S2, A any](
+	s SG.Semigroup[W],
 	setter func(A) func(S1) S2,
 	f func(S1) GT,
 ) func(GS1) GS2 {
 	return C.Bind(
-		Chain[GS2, GS1, func(S1) GS2, W, S1, S2],
+		FCT.Bind1st(Chain[GS2, GS1, func(S1) GS2, W, S1, S2], s),
 		Map[GS2, GT, func(A) S2, W, A, S2],
 		setter,
 		f,
@@ -43,7 +45,7 @@ func Bind[GS1 ~func() T.Tuple3[S1, W, SG.Semigroup[W]], GS2 ~func() T.Tuple3[S2,
 }
 
 // Let attaches the result of a computation to a context [S1] to produce a context [S2]
-func Let[GS1 ~func() T.Tuple3[S1, W, SG.Semigroup[W]], GS2 ~func() T.Tuple3[S2, W, SG.Semigroup[W]], W, S1, S2, A any](
+func Let[GS1 ~func() P.Pair[S1, W], GS2 ~func() P.Pair[S2, W], W, S1, S2, A any](
 	key func(A) func(S1) S2,
 	f func(S1) A,
 ) func(GS1) GS2 {
@@ -55,7 +57,7 @@ func Let[GS1 ~func() T.Tuple3[S1, W, SG.Semigroup[W]], GS2 ~func() T.Tuple3[S2,
 }
 
 // LetTo attaches the a value to a context [S1] to produce a context [S2]
-func LetTo[GS1 ~func() T.Tuple3[S1, W, SG.Semigroup[W]], GS2 ~func() T.Tuple3[S2, W, SG.Semigroup[W]], W, S1, S2, B any](
+func LetTo[GS1 ~func() P.Pair[S1, W], GS2 ~func() P.Pair[S2, W], W, S1, S2, B any](
 	key func(B) func(S1) S2,
 	b B,
 ) func(GS1) GS2 {
@@ -67,7 +69,7 @@ func LetTo[GS1 ~func() T.Tuple3[S1, W, SG.Semigroup[W]], GS2 ~func() T.Tuple3[S2
 }
 
 // BindTo initializes a new state [S1] from a value [T]
-func BindTo[GS1 ~func() T.Tuple3[S1, W, SG.Semigroup[W]], GT ~func() T.Tuple3[A, W, SG.Semigroup[W]], W, S1, A any](
+func BindTo[GS1 ~func() P.Pair[S1, W], GT ~func() P.Pair[A, W], W, S1, A any](
 	setter func(A) S1,
 ) func(GT) GS1 {
 	return C.BindTo(
@@ -77,13 +79,14 @@ func BindTo[GS1 ~func() T.Tuple3[S1, W, SG.Semigroup[W]], GT ~func() T.Tuple3[A,
 }
 
 // ApS attaches a value to a context [S1] to produce a context [S2] by considering the context and the value concurrently
-func ApS[GS1 ~func() T.Tuple3[S1, W, SG.Semigroup[W]], GS2 ~func() T.Tuple3[S2, W, SG.Semigroup[W]], GT ~func() T.Tuple3[A, W, SG.Semigroup[W]], W, S1, S2, A any](
+func ApS[GS1 ~func() P.Pair[S1, W], GS2 ~func() P.Pair[S2, W], GT ~func() P.Pair[A, W], W, S1, S2, A any](
+	s SG.Semigroup[W],
 	setter func(A) func(S1) S2,
 	fa GT,
 ) func(GS1) GS2 {
 	return apply.ApS(
-		Ap[GS2, func() T.Tuple3[func(A) S2, W, SG.Semigroup[W]], GT, W, A, S2],
-		Map[func() T.Tuple3[func(A) S2, W, SG.Semigroup[W]], GS1, func(S1) func(A) S2],
+		FCT.Bind1st(Ap[GS2, func() P.Pair[func(A) S2, W], GT, W, A, S2], s),
+		Map[func() P.Pair[func(A) S2, W], GS1, func(S1) func(A) S2],
 		setter,
 		fa,
 	)

writer/generic/eq.go

@@ -17,21 +17,18 @@ package generic
 
 import (
 	EQ "github.com/IBM/fp-go/eq"
-	SG "github.com/IBM/fp-go/semigroup"
-	T "github.com/IBM/fp-go/tuple"
+	P "github.com/IBM/fp-go/pair"
 )
 
 // Constructs an equal predicate for a [Writer]
-func Eq[GA ~func() T.Tuple3[A, W, SG.Semigroup[W]], W, A any](w EQ.Eq[W], a EQ.Eq[A]) EQ.Eq[GA] {
+func Eq[GA ~func() P.Pair[A, W], W, A any](w EQ.Eq[W], a EQ.Eq[A]) EQ.Eq[GA] {
+	eqp := P.Eq(a, w)
 	return EQ.FromEquals(func(l, r GA) bool {
-		ll := l()
-		rr := r()
-
-		return a.Equals(ll.F1, rr.F1) && w.Equals(ll.F2, rr.F2)
+		return eqp.Equals(l(), r())
 	})
 }
 
 // FromStrictEquals constructs an [EQ.Eq] from the canonical comparison function
-func FromStrictEquals[GA ~func() T.Tuple3[A, W, SG.Semigroup[W]], W, A comparable]() EQ.Eq[GA] {
+func FromStrictEquals[GA ~func() P.Pair[A, W], W, A comparable]() EQ.Eq[GA] {
 	return Eq[GA](EQ.FromStrictEquals[W](), EQ.FromStrictEquals[A]())
 }

writer/generic/monad.go

@@ -0,0 +1,106 @@
+// Copyright (c) 2024 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 generic
+
+import (
+	"github.com/IBM/fp-go/internal/applicative"
+	"github.com/IBM/fp-go/internal/functor"
+	"github.com/IBM/fp-go/internal/monad"
+	"github.com/IBM/fp-go/internal/pointed"
+	M "github.com/IBM/fp-go/monoid"
+	P "github.com/IBM/fp-go/pair"
+	SG "github.com/IBM/fp-go/semigroup"
+)
+
+type writerPointed[GA ~func() P.Pair[A, W], W, A any] struct {
+	m M.Monoid[W]
+}
+
+type writerFunctor[GB ~func() P.Pair[B, W], GA ~func() P.Pair[A, W], W, A, B any] struct{}
+
+type writerApplicative[GB ~func() P.Pair[B, W], GAB ~func() P.Pair[func(A) B, W], GA ~func() P.Pair[A, W], W, A, B any] struct {
+	s SG.Semigroup[W]
+	m M.Monoid[W]
+}
+
+type writerMonad[GB ~func() P.Pair[B, W], GAB ~func() P.Pair[func(A) B, W], GA ~func() P.Pair[A, W], W, A, B any] struct {
+	s SG.Semigroup[W]
+	m M.Monoid[W]
+}
+
+func (o *writerPointed[GA, W, A]) Of(a A) GA {
+	return Of[GA](o.m, a)
+}
+
+func (o *writerApplicative[GB, GAB, GA, W, A, B]) Of(a A) GA {
+	return Of[GA](o.m, a)
+}
+
+func (o *writerMonad[GB, GAB, GA, W, A, B]) Of(a A) GA {
+	return Of[GA](o.m, a)
+}
+
+func (o *writerFunctor[GB, GA, W, A, B]) Map(f func(A) B) func(GA) GB {
+	return Map[GB, GA](f)
+}
+
+func (o *writerApplicative[GB, GAB, GA, W, A, B]) Map(f func(A) B) func(GA) GB {
+	return Map[GB, GA](f)
+}
+
+func (o *writerMonad[GB, GAB, GA, W, A, B]) Map(f func(A) B) func(GA) GB {
+	return Map[GB, GA](f)
+}
+
+func (o *writerMonad[GB, GAB, GA, W, A, B]) Chain(f func(A) GB) func(GA) GB {
+	return Chain[GB, GA](o.s, f)
+}
+
+func (o *writerApplicative[GB, GAB, GA, W, A, B]) Ap(fa GA) func(GAB) GB {
+	return Ap[GB, GAB, GA](o.s, fa)
+}
+
+func (o *writerMonad[GB, GAB, GA, W, A, B]) Ap(fa GA) func(GAB) GB {
+	return Ap[GB, GAB, GA](o.s, fa)
+}
+
+// Pointed implements the pointed operations for [Writer]
+func Pointed[GA ~func() P.Pair[A, W], W, A any](m M.Monoid[W]) pointed.Pointed[A, GA] {
+	return &writerPointed[GA, W, A]{
+		m: m,
+	}
+}
+
+// Functor implements the functor operations for [Writer]
+func Functor[GB ~func() P.Pair[B, W], GA ~func() P.Pair[A, W], W, A, B any]() functor.Functor[A, B, GA, GB] {
+	return &writerFunctor[GB, GA, W, A, B]{}
+}
+
+// Applicative implements the applicative operations for [Writer]
+func Applicative[GB ~func() P.Pair[B, W], GAB ~func() P.Pair[func(A) B, W], GA ~func() P.Pair[A, W], W, A, B any](m M.Monoid[W]) applicative.Applicative[A, B, GA, GB, GAB] {
+	return &writerApplicative[GB, GAB, GA, W, A, B]{
+		s: M.ToSemigroup(m),
+		m: m,
+	}
+}
+
+// Monad implements the monadic operations for [Writer]
+func Monad[GB ~func() P.Pair[B, W], GAB ~func() P.Pair[func(A) B, W], GA ~func() P.Pair[A, W], W, A, B any](m M.Monoid[W]) monad.Monad[A, B, GA, GB, GAB] {
+	return &writerMonad[GB, GAB, GA, W, A, B]{
+		s: M.ToSemigroup(m),
+		m: m,
+	}
+}

writer/generic/writer.go

@@ -21,133 +21,137 @@ import (
 	FC "github.com/IBM/fp-go/internal/functor"
 	IO "github.com/IBM/fp-go/io/generic"
 	M "github.com/IBM/fp-go/monoid"
+	P "github.com/IBM/fp-go/pair"
 	SG "github.com/IBM/fp-go/semigroup"
-	T "github.com/IBM/fp-go/tuple"
 )
 
-func Tell[GA ~func() T.Tuple3[any, W, SG.Semigroup[W]], W any](s SG.Semigroup[W]) func(W) GA {
-	return F.Flow2(
-		F.Bind13of3(T.MakeTuple3[any, W, SG.Semigroup[W]])(nil, s),
-		IO.Of[GA],
-	)
+var (
+	undefined any = struct{}{}
+)
+
+func Tell[GA ~func() P.Pair[any, W], W any](w W) GA {
+	return IO.Of[GA](P.MakePair[any](undefined, w))
 }
 
-func Of[GA ~func() T.Tuple3[A, W, SG.Semigroup[W]], W, A any](m M.Monoid[W]) func(A) GA {
-	return F.Flow2(
-		F.Bind23of3(T.MakeTuple3[A, W, SG.Semigroup[W]])(m.Empty(), M.ToSemigroup(m)),
-		IO.Of[GA],
-	)
+func Of[GA ~func() P.Pair[A, W], W, A any](m M.Monoid[W], a A) GA {
+	return IO.Of[GA](P.MakePair(a, m.Empty()))
 }
 
 // Listen modifies the result to include the changes to the accumulator
-func Listen[GA ~func() T.Tuple3[A, W, SG.Semigroup[W]], GTA ~func() T.Tuple3[T.Tuple2[A, W], W, SG.Semigroup[W]], W, A any](fa GA) GTA {
-	return func() T.Tuple3[T.Tuple2[A, W], W, SG.Semigroup[W]] {
+func Listen[GA ~func() P.Pair[A, W], GTA ~func() P.Pair[P.Pair[A, W], W], W, A any](fa GA) GTA {
+	return func() P.Pair[P.Pair[A, W], W] {
 		t := fa()
-		return T.MakeTuple3(T.MakeTuple2(t.F1, t.F2), t.F2, t.F3)
+		return P.MakePair(t, P.Tail(t))
 	}
 }
 
 // Pass applies the returned function to the accumulator
-func Pass[GFA ~func() T.Tuple3[T.Tuple2[A, FCT], W, SG.Semigroup[W]], GA ~func() T.Tuple3[A, W, SG.Semigroup[W]], FCT ~func(W) W, W, A any](fa GFA) GA {
-	return func() T.Tuple3[A, W, SG.Semigroup[W]] {
+func Pass[GFA ~func() P.Pair[P.Pair[A, FCT], W], GA ~func() P.Pair[A, W], FCT ~func(W) W, W, A any](fa GFA) GA {
+	return func() P.Pair[A, W] {
 		t := fa()
-		return T.MakeTuple3(t.F1.F1, t.F1.F2(t.F2), t.F3)
+		a := P.Head(t)
+		return P.MakePair(P.Head(a), P.Tail(a)(P.Tail(t)))
 	}
 }
 
-func MonadMap[GB ~func() T.Tuple3[B, W, SG.Semigroup[W]], GA ~func() T.Tuple3[A, W, SG.Semigroup[W]], FCT ~func(A) B, W, A, B any](fa GA, f FCT) GB {
-	return IO.MonadMap[GA, GB](fa, T.Map3(f, F.Identity[W], F.Identity[SG.Semigroup[W]]))
+func MonadMap[GB ~func() P.Pair[B, W], GA ~func() P.Pair[A, W], FCT ~func(A) B, W, A, B any](fa GA, f FCT) GB {
+	return IO.MonadMap[GA, GB](fa, P.Map[W](f))
 }
 
-func Map[GB ~func() T.Tuple3[B, W, SG.Semigroup[W]], GA ~func() T.Tuple3[A, W, SG.Semigroup[W]], FCT ~func(A) B, W, A, B any](f FCT) func(GA) GB {
-	return IO.Map[GA, GB](T.Map3(f, F.Identity[W], F.Identity[SG.Semigroup[W]]))
+func Map[GB ~func() P.Pair[B, W], GA ~func() P.Pair[A, W], FCT ~func(A) B, W, A, B any](f FCT) func(GA) GB {
+	return IO.Map[GA, GB](P.Map[W](f))
 }
 
-func MonadChain[GB ~func() T.Tuple3[B, W, SG.Semigroup[W]], GA ~func() T.Tuple3[A, W, SG.Semigroup[W]], FCT ~func(A) GB, W, A, B any](fa GA, f FCT) GB {
-	return func() T.Tuple3[B, W, SG.Semigroup[W]] {
+func MonadChain[GB ~func() P.Pair[B, W], GA ~func() P.Pair[A, W], FCT ~func(A) GB, W, A, B any](s SG.Semigroup[W], fa GA, f FCT) GB {
+	return func() P.Pair[B, W] {
 		a := fa()
-		b := f(a.F1)()
+		b := f(P.Head(a))()
 
-		return T.MakeTuple3(b.F1, b.F3.Concat(a.F2, b.F2), b.F3)
+		return P.MakePair(P.Head(b), s.Concat(P.Tail(a), P.Tail(b)))
 	}
 }
 
-func Chain[GB ~func() T.Tuple3[B, W, SG.Semigroup[W]], GA ~func() T.Tuple3[A, W, SG.Semigroup[W]], FCT ~func(A) GB, W, A, B any](f FCT) func(GA) GB {
-	return F.Bind2nd(MonadChain[GB, GA, FCT, W, A, B], f)
+func Chain[GB ~func() P.Pair[B, W], GA ~func() P.Pair[A, W], FCT ~func(A) GB, W, A, B any](s SG.Semigroup[W], f FCT) func(GA) GB {
+	return func(fa GA) GB {
+		return MonadChain(s, fa, f)
+	}
 }
 
-func MonadAp[GB ~func() T.Tuple3[B, W, SG.Semigroup[W]], GAB ~func() T.Tuple3[func(A) B, W, SG.Semigroup[W]], GA ~func() T.Tuple3[A, W, SG.Semigroup[W]], W, A, B any](fab GAB, fa GA) GB {
-	return func() T.Tuple3[B, W, SG.Semigroup[W]] {
+func MonadAp[GB ~func() P.Pair[B, W], GAB ~func() P.Pair[func(A) B, W], GA ~func() P.Pair[A, W], W, A, B any](s SG.Semigroup[W], fab GAB, fa GA) GB {
+	return func() P.Pair[B, W] {
 		f := fab()
 		a := fa()
 
-		return T.MakeTuple3(f.F1(a.F1), f.F3.Concat(f.F2, a.F2), f.F3)
+		return P.MakePair(P.Head(f)(P.Head(a)), s.Concat(P.Tail(f), P.Tail(a)))
 	}
 }
 
-func Ap[GB ~func() T.Tuple3[B, W, SG.Semigroup[W]], GAB ~func() T.Tuple3[func(A) B, W, SG.Semigroup[W]], GA ~func() T.Tuple3[A, W, SG.Semigroup[W]], W, A, B any](ga GA) func(GAB) GB {
-	return F.Bind2nd(MonadAp[GB, GAB, GA], ga)
+func Ap[GB ~func() P.Pair[B, W], GAB ~func() P.Pair[func(A) B, W], GA ~func() P.Pair[A, W], W, A, B any](s SG.Semigroup[W], ga GA) func(GAB) GB {
+	return func(fab GAB) GB {
+		return MonadAp[GB](s, fab, ga)
+	}
 }
 
-func MonadChainFirst[GB ~func() T.Tuple3[B, W, SG.Semigroup[W]], GA ~func() T.Tuple3[A, W, SG.Semigroup[W]], FCT ~func(A) GB, W, A, B any](ma GA, f FCT) GA {
+func MonadChainFirst[GB ~func() P.Pair[B, W], GA ~func() P.Pair[A, W], FCT ~func(A) GB, W, A, B any](s SG.Semigroup[W], ma GA, f FCT) GA {
 	return C.MonadChainFirst(
-		MonadChain[GA, GA, func(A) GA],
+		F.Bind1of3(MonadChain[GA, GA, func(A) GA])(s),
 		MonadMap[GA, GB, func(B) A],
 		ma,
 		f,
 	)
 }
 
-func ChainFirst[GB ~func() T.Tuple3[B, W, SG.Semigroup[W]], GA ~func() T.Tuple3[A, W, SG.Semigroup[W]], FCT ~func(A) GB, W, A, B any](f FCT) func(GA) GA {
+func ChainFirst[GB ~func() P.Pair[B, W], GA ~func() P.Pair[A, W], FCT ~func(A) GB, W, A, B any](s SG.Semigroup[W], f FCT) func(GA) GA {
 	return C.ChainFirst(
-		Chain[GA, GA, func(A) GA],
+		F.Bind1st(Chain[GA, GA, func(A) GA], s),
 		Map[GA, GB, func(B) A],
 		f,
 	)
 }
 
-func Flatten[GAA ~func() T.Tuple3[GA, W, SG.Semigroup[W]], GA ~func() T.Tuple3[A, W, SG.Semigroup[W]], W, A any](mma GAA) GA {
-	return MonadChain[GA, GAA, func(GA) GA](mma, F.Identity[GA])
+func Flatten[GAA ~func() P.Pair[GA, W], GA ~func() P.Pair[A, W], W, A any](s SG.Semigroup[W], mma GAA) GA {
+	return MonadChain[GA, GAA, func(GA) GA](s, mma, F.Identity[GA])
 }
 
-func Execute[GA ~func() T.Tuple3[A, W, SG.Semigroup[W]], W, A any](fa GA) W {
-	return fa().F2
+func Execute[GA ~func() P.Pair[A, W], W, A any](fa GA) W {
+	return P.Tail(fa())
 }
 
-func Evaluate[GA ~func() T.Tuple3[A, W, SG.Semigroup[W]], W, A any](fa GA) A {
-	return fa().F1
+func Evaluate[GA ~func() P.Pair[A, W], W, A any](fa GA) A {
+	return P.Head(fa())
 }
 
 // MonadCensor modifies the final accumulator value by applying a function
-func MonadCensor[GA ~func() T.Tuple3[A, W, SG.Semigroup[W]], FCT ~func(W) W, W, A any](fa GA, f FCT) GA {
-	return IO.MonadMap[GA, GA](fa, T.Map3(F.Identity[A], f, F.Identity[SG.Semigroup[W]]))
+func MonadCensor[GA ~func() P.Pair[A, W], FCT ~func(W) W, W, A any](fa GA, f FCT) GA {
+	return IO.MonadMap[GA, GA](fa, P.MapTail[A](f))
 }
 
 // Censor modifies the final accumulator value by applying a function
-func Censor[GA ~func() T.Tuple3[A, W, SG.Semigroup[W]], FCT ~func(W) W, W, A any](f FCT) func(GA) GA {
-	return IO.Map[GA, GA](T.Map3(F.Identity[A], f, F.Identity[SG.Semigroup[W]]))
+func Censor[GA ~func() P.Pair[A, W], FCT ~func(W) W, W, A any](f FCT) func(GA) GA {
+	return IO.Map[GA, GA](P.MapTail[A](f))
 }
 
 // MonadListens projects a value from modifications made to the accumulator during an action
-func MonadListens[GA ~func() T.Tuple3[A, W, SG.Semigroup[W]], GAB ~func() T.Tuple3[T.Tuple2[A, B], W, SG.Semigroup[W]], FCT ~func(W) B, W, A, B any](fa GA, f FCT) GAB {
-	return func() T.Tuple3[T.Tuple2[A, B], W, SG.Semigroup[W]] {
+func MonadListens[GA ~func() P.Pair[A, W], GAB ~func() P.Pair[P.Pair[A, B], W], FCT ~func(W) B, W, A, B any](fa GA, f FCT) GAB {
+	return func() P.Pair[P.Pair[A, B], W] {
 		a := fa()
-		return T.MakeTuple3(T.MakeTuple2(a.F1, f(a.F2)), a.F2, a.F3)
+		t := P.Tail(a)
+		return P.MakePair(P.MakePair(P.Head(a), f(t)), t)
 	}
 }
 
 // Listens projects a value from modifications made to the accumulator during an action
-func Listens[GA ~func() T.Tuple3[A, W, SG.Semigroup[W]], GAB ~func() T.Tuple3[T.Tuple2[A, B], W, SG.Semigroup[W]], FCT ~func(W) B, W, A, B any](f FCT) func(GA) GAB {
+func Listens[GA ~func() P.Pair[A, W], GAB ~func() P.Pair[P.Pair[A, B], W], FCT ~func(W) B, W, A, B any](f FCT) func(GA) GAB {
 	return F.Bind2nd(MonadListens[GA, GAB, FCT], f)
 }
 
-func MonadFlap[FAB ~func(A) B, GFAB ~func() T.Tuple3[FAB, W, SG.Semigroup[W]], GB ~func() T.Tuple3[B, W, SG.Semigroup[W]], W, A, B any](fab GFAB, a A) GB {
+func MonadFlap[FAB ~func(A) B, GFAB ~func() P.Pair[FAB, W], GB ~func() P.Pair[B, W], W, A, B any](fab GFAB, a A) GB {
 	return FC.MonadFlap(
 		MonadMap[GB, GFAB, func(FAB) B],
 		fab,
 		a)
 }
 
-func Flap[FAB ~func(A) B, GFAB ~func() T.Tuple3[FAB, W, SG.Semigroup[W]], GB ~func() T.Tuple3[B, W, SG.Semigroup[W]], W, A, B any](a A) func(GFAB) GB {
+func Flap[FAB ~func(A) B, GFAB ~func() P.Pair[FAB, W], GB ~func() P.Pair[B, W], W, A, B any](a A) func(GFAB) GB {
 	return FC.Flap(Map[GB, GFAB, func(FAB) B], a)
 }

writer/monad.go

@@ -0,0 +1,45 @@
+// Copyright (c) 2024 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 writer
+
+import (
+	"github.com/IBM/fp-go/internal/applicative"
+	"github.com/IBM/fp-go/internal/functor"
+	"github.com/IBM/fp-go/internal/monad"
+	"github.com/IBM/fp-go/internal/pointed"
+	M "github.com/IBM/fp-go/monoid"
+	G "github.com/IBM/fp-go/writer/generic"
+)
+
+// Pointed implements the pointed operations for [Writer]
+func Pointed[W, A any](m M.Monoid[W]) pointed.Pointed[A, Writer[W, A]] {
+	return G.Pointed[Writer[W, A], W, A](m)
+}
+
+// Functor implements the pointed operations for [Writer]
+func Functor[W, A, B any]() functor.Functor[A, B, Writer[W, A], Writer[W, B]] {
+	return G.Functor[Writer[W, B], Writer[W, A], W, A, B]()
+}
+
+// Applicative implements the applicative operations for [Writer]
+func Applicative[W, A, B any](m M.Monoid[W]) applicative.Applicative[A, B, Writer[W, A], Writer[W, B], Writer[W, func(A) B]] {
+	return G.Applicative[Writer[W, B], Writer[W, func(A) B], Writer[W, A]](m)
+}
+
+// Monad implements the monadic operations for [Writer]
+func Monad[W, A, B any](m M.Monoid[W]) monad.Monad[A, B, Writer[W, A], Writer[W, B], Writer[W, func(A) B]] {
+	return G.Monad[Writer[W, B], Writer[W, func(A) B], Writer[W, A]](m)
+}

writer/testing/laws.go

@@ -37,39 +37,40 @@ func AssertLaws[W, A, B, C any](t *testing.T,
 	bc func(B) C,
 ) func(a A) bool {
 
-	return L.AssertLaws(t,
+	fofc := WRT.Pointed[W, C](m)
+	fofaa := WRT.Pointed[W, func(A) A](m)
+	fofbc := WRT.Pointed[W, func(B) C](m)
+	fofabb := WRT.Pointed[W, func(func(A) B) B](m)
+
+	fmap := WRT.Functor[W, func(B) C, func(func(A) B) func(A) C]()
+
+	fapabb := WRT.Applicative[W, func(A) B, B](m)
+	fapabac := WRT.Applicative[W, func(A) B, func(A) C](m)
+
+	maa := WRT.Monad[W, A, A](m)
+	mab := WRT.Monad[W, A, B](m)
+	mac := WRT.Monad[W, A, C](m)
+	mbc := WRT.Monad[W, B, C](m)
+
+	return L.MonadAssertLaws(t,
 		WRT.Eq(eqw, eqa),
 		WRT.Eq(eqw, eqb),
 		WRT.Eq(eqw, eqc),
 
-		WRT.Of[A](m),
-		WRT.Of[B](m),
-		WRT.Of[C](m),
+		fofc,
+		fofaa,
+		fofbc,
+		fofabb,
 
-		WRT.Of[func(A) A](m),
-		WRT.Of[func(A) B](m),
-		WRT.Of[func(B) C](m),
-		WRT.Of[func(func(A) B) B](m),
+		fmap,
 
-		WRT.MonadMap[func(A) A, W, A, A],
-		WRT.MonadMap[func(A) B, W, A, B],
-		WRT.MonadMap[func(A) C, W, A, C],
-		WRT.MonadMap[func(B) C, W, B, C],
+		fapabb,
+		fapabac,
 
-		WRT.MonadMap[func(func(B) C) func(func(A) B) func(A) C, W, func(B) C, func(func(A) B) func(A) C],
-
-		WRT.MonadChain[func(A) WRT.Writer[W, A], W, A, A],
-		WRT.MonadChain[func(A) WRT.Writer[W, B], W, A, B],
-		WRT.MonadChain[func(A) WRT.Writer[W, C], W, A, C],
-		WRT.MonadChain[func(B) WRT.Writer[W, C], W, B, C],
-
-		WRT.MonadAp[A, A, W],
-		WRT.MonadAp[B, A, W],
-		WRT.MonadAp[C, B, W],
-		WRT.MonadAp[C, A, W],
-
-		WRT.MonadAp[B, func(A) B, W],
-		WRT.MonadAp[func(A) C, func(A) B, W],
+		maa,
+		mab,
+		mac,
+		mbc,
 
 		ab,
 		bc,

writer/writer.go

@@ -19,30 +19,30 @@ import (
 	EM "github.com/IBM/fp-go/endomorphism"
 	IO "github.com/IBM/fp-go/io"
 	M "github.com/IBM/fp-go/monoid"
-	S "github.com/IBM/fp-go/semigroup"
-	T "github.com/IBM/fp-go/tuple"
+	P "github.com/IBM/fp-go/pair"
+	SG "github.com/IBM/fp-go/semigroup"
 	G "github.com/IBM/fp-go/writer/generic"
 )
 
-type Writer[W, A any] IO.IO[T.Tuple3[A, W, S.Semigroup[W]]]
+type Writer[W, A any] IO.IO[P.Pair[A, W]]
 
 // Tell appends a value to the accumulator
-func Tell[W any](s S.Semigroup[W]) func(W) Writer[W, any] {
-	return G.Tell[Writer[W, any]](s)
+func Tell[W any](w W) Writer[W, any] {
+	return G.Tell[Writer[W, any]](w)
 }
 
-func Of[A, W any](m M.Monoid[W]) func(A) Writer[W, A] {
-	return G.Of[Writer[W, A]](m)
+func Of[A, W any](m M.Monoid[W], a A) Writer[W, A] {
+	return G.Of[Writer[W, A]](m, a)
 }
 
 // Listen modifies the result to include the changes to the accumulator
-func Listen[W, A any](fa Writer[W, A]) Writer[W, T.Tuple2[A, W]] {
-	return G.Listen[Writer[W, A], Writer[W, T.Tuple2[A, W]], W, A](fa)
+func Listen[W, A any](fa Writer[W, A]) Writer[W, P.Pair[A, W]] {
+	return G.Listen[Writer[W, A], Writer[W, P.Pair[A, W]], W, A](fa)
 }
 
 // Pass applies the returned function to the accumulator
-func Pass[W, A any](fa Writer[W, T.Tuple2[A, EM.Endomorphism[W]]]) Writer[W, A] {
-	return G.Pass[Writer[W, T.Tuple2[A, EM.Endomorphism[W]]], Writer[W, A]](fa)
+func Pass[W, A any](fa Writer[W, P.Pair[A, EM.Endomorphism[W]]]) Writer[W, A] {
+	return G.Pass[Writer[W, P.Pair[A, EM.Endomorphism[W]]], Writer[W, A]](fa)
 }
 
 func MonadMap[FCT ~func(A) B, W, A, B any](fa Writer[W, A], f FCT) Writer[W, B] {
@@ -53,32 +53,32 @@ func Map[W any, FCT ~func(A) B, A, B any](f FCT) func(Writer[W, A]) Writer[W, B]
 	return G.Map[Writer[W, B], Writer[W, A]](f)
 }
 
-func MonadChain[FCT ~func(A) Writer[W, B], W, A, B any](fa Writer[W, A], fct FCT) Writer[W, B] {
-	return G.MonadChain[Writer[W, B], Writer[W, A], FCT](fa, fct)
+func MonadChain[FCT ~func(A) Writer[W, B], W, A, B any](s SG.Semigroup[W], fa Writer[W, A], fct FCT) Writer[W, B] {
+	return G.MonadChain[Writer[W, B], Writer[W, A], FCT](s, fa, fct)
 }
 
-func Chain[A, B, W any](fa func(A) Writer[W, B]) func(Writer[W, A]) Writer[W, B] {
-	return G.Chain[Writer[W, B], Writer[W, A], func(A) Writer[W, B]](fa)
+func Chain[A, B, W any](s SG.Semigroup[W], fa func(A) Writer[W, B]) func(Writer[W, A]) Writer[W, B] {
+	return G.Chain[Writer[W, B], Writer[W, A], func(A) Writer[W, B]](s, fa)
 }
 
-func MonadAp[B, A, W any](fab Writer[W, func(A) B], fa Writer[W, A]) Writer[W, B] {
-	return G.MonadAp[Writer[W, B], Writer[W, func(A) B], Writer[W, A]](fab, fa)
+func MonadAp[B, A, W any](s SG.Semigroup[W], fab Writer[W, func(A) B], fa Writer[W, A]) Writer[W, B] {
+	return G.MonadAp[Writer[W, B], Writer[W, func(A) B], Writer[W, A]](s, fab, fa)
 }
 
-func Ap[B, A, W any](fa Writer[W, A]) func(Writer[W, func(A) B]) Writer[W, B] {
-	return G.Ap[Writer[W, B], Writer[W, func(A) B], Writer[W, A]](fa)
+func Ap[B, A, W any](s SG.Semigroup[W], fa Writer[W, A]) func(Writer[W, func(A) B]) Writer[W, B] {
+	return G.Ap[Writer[W, B], Writer[W, func(A) B], Writer[W, A]](s, fa)
 }
 
-func MonadChainFirst[FCT ~func(A) Writer[W, B], W, A, B any](fa Writer[W, A], fct FCT) Writer[W, A] {
-	return G.MonadChainFirst[Writer[W, B], Writer[W, A], FCT](fa, fct)
+func MonadChainFirst[FCT ~func(A) Writer[W, B], W, A, B any](s SG.Semigroup[W], fa Writer[W, A], fct FCT) Writer[W, A] {
+	return G.MonadChainFirst[Writer[W, B], Writer[W, A], FCT](s, fa, fct)
 }
 
-func ChainFirst[FCT ~func(A) Writer[W, B], W, A, B any](fct FCT) func(Writer[W, A]) Writer[W, A] {
-	return G.ChainFirst[Writer[W, B], Writer[W, A], FCT](fct)
+func ChainFirst[FCT ~func(A) Writer[W, B], W, A, B any](s SG.Semigroup[W], fct FCT) func(Writer[W, A]) Writer[W, A] {
+	return G.ChainFirst[Writer[W, B], Writer[W, A], FCT](s, fct)
 }
 
-func Flatten[W, A any](mma Writer[W, Writer[W, A]]) Writer[W, A] {
-	return G.Flatten[Writer[W, Writer[W, A]], Writer[W, A]](mma)
+func Flatten[W, A any](s SG.Semigroup[W], mma Writer[W, Writer[W, A]]) Writer[W, A] {
+	return G.Flatten[Writer[W, Writer[W, A]], Writer[W, A]](s, mma)
 }
 
 // Execute extracts the accumulator
@@ -102,13 +102,13 @@ func Censor[A any, FCT ~func(W) W, W any](f FCT) func(Writer[W, A]) Writer[W, A]
 }
 
 // MonadListens projects a value from modifications made to the accumulator during an action
-func MonadListens[A any, FCT ~func(W) B, W, B any](fa Writer[W, A], f FCT) Writer[W, T.Tuple2[A, B]] {
-	return G.MonadListens[Writer[W, A], Writer[W, T.Tuple2[A, B]]](fa, f)
+func MonadListens[A any, FCT ~func(W) B, W, B any](fa Writer[W, A], f FCT) Writer[W, P.Pair[A, B]] {
+	return G.MonadListens[Writer[W, A], Writer[W, P.Pair[A, B]]](fa, f)
 }
 
 // Listens projects a value from modifications made to the accumulator during an action
-func Listens[A any, FCT ~func(W) B, W, B any](f FCT) func(Writer[W, A]) Writer[W, T.Tuple2[A, B]] {
-	return G.Listens[Writer[W, A], Writer[W, T.Tuple2[A, B]]](f)
+func Listens[A any, FCT ~func(W) B, W, B any](f FCT) func(Writer[W, A]) Writer[W, P.Pair[A, B]] {
+	return G.Listens[Writer[W, A], Writer[W, P.Pair[A, B]]](f)
 }
 
 func MonadFlap[W, B, A any](fab Writer[W, func(A) B], a A) Writer[W, B] {

writer/writer_test.go

@@ -20,24 +20,22 @@ import (
 
 	A "github.com/IBM/fp-go/array"
 	F "github.com/IBM/fp-go/function"
-	S "github.com/IBM/fp-go/semigroup"
-	T "github.com/IBM/fp-go/tuple"
+	P "github.com/IBM/fp-go/pair"
 )
 
 func doubleAndLog(data int) Writer[[]string, int] {
-	return func() T.Tuple3[int, []string, S.Semigroup[[]string]] {
+	return func() P.Pair[int, []string] {
 		result := data * 2
-		return T.MakeTuple3(result, A.Of(fmt.Sprintf("Doubled %d -> %d", data, result)), sg)
+		return P.MakePair(result, A.Of(fmt.Sprintf("Doubled %d -> %d", data, result)))
 	}
 }
 
 func ExampleWriter_logging() {
 
-	res := F.Pipe4(
-		10,
-		Of[int](monoid),
-		Chain(doubleAndLog),
-		Chain(doubleAndLog),
+	res := F.Pipe3(
+		Of[int](monoid, 10),
+		Chain(sg, doubleAndLog),
+		Chain(sg, doubleAndLog),
 		Execute[[]string, int],
 	)