fix: next small step towards StateReaderIOEither

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

internal/statet/state.go

@@ -50,9 +50,7 @@ func MonadMap[
 
 	return F.Flow2(
 		fa,
-		F.Bind2nd(fmap, func(a P.Pair[A, S]) P.Pair[B, S] {
+		F.Bind2nd(fmap, P.Map[S](f)),
-			return P.MakePair(f(P.Head(a)), P.Tail(a))
-		}),
 	)
 }
 
@@ -67,9 +65,7 @@ func Map[
 
 	f func(A) B,
 ) func(HKTSA) HKTSB {
-	mp := fmap(func(a P.Pair[A, S]) P.Pair[B, S] {
+	mp := fmap(P.Map[S](f))
-		return P.MakePair(f(P.Head(a)), P.Tail(a))
-	})
 
 	return func(fa HKTSA) HKTSB {
 		return F.Flow2(
@@ -121,3 +117,51 @@ func Chain[
 		)
 	}
 }
+
+func MonadAp[
+	HKTSA ~func(S) HKTA,
+	HKTSB ~func(S) HKTB,
+	HKTSAB ~func(S) HKTAB,
+	HKTA,
+	HKTB,
+	HKTAB,
+
+	S, A, B any,
+](
+	fmap func(HKTA, func(P.Pair[A, S]) P.Pair[B, S]) HKTB,
+	fchain func(HKTAB, func(P.Pair[func(A) B, S]) HKTB) HKTB,
+
+	fab HKTSAB,
+	fa HKTSA,
+) HKTSB {
+	return func(s S) HKTB {
+		return fchain(fab(s), func(ab P.Pair[func(A) B, S]) HKTB {
+			return fmap(fa(P.Tail(ab)), P.Map[S](P.Head(ab)))
+		})
+	}
+}
+
+func Ap[
+	HKTSA ~func(S) HKTA,
+	HKTSB ~func(S) HKTB,
+	HKTSAB ~func(S) HKTAB,
+	HKTA,
+	HKTB,
+	HKTAB,
+
+	S, A, B any,
+](
+	fmap func(func(P.Pair[A, S]) P.Pair[B, S]) func(HKTA) HKTB,
+	fchain func(func(P.Pair[func(A) B, S]) HKTB) func(HKTAB) HKTB,
+
+	fa HKTSA,
+) func(HKTSAB) HKTSB {
+	return func(fab HKTSAB) HKTSB {
+		return F.Flow2(
+			fab,
+			fchain(func(ab P.Pair[func(A) B, S]) HKTB {
+				return fmap(P.Map[S](P.Head(ab)))(fa(P.Tail(ab)))
+			}),
+		)
+	}
+}

statereaderioeither/eq.go

@@ -0,0 +1,35 @@
+// 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 statereaderioeither
+
+import (
+	EQ "github.com/IBM/fp-go/eq"
+	P "github.com/IBM/fp-go/pair"
+	RIOE "github.com/IBM/fp-go/readerioeither"
+	G "github.com/IBM/fp-go/statereaderioeither/generic"
+)
+
+// Eq implements the equals predicate for values contained in the [StateReaderIOEither] monad
+func Eq[
+	S, R, E, A any](eqr EQ.Eq[RIOE.ReaderIOEither[R, E, P.Pair[A, S]]]) func(S) EQ.Eq[StateReaderIOEither[S, R, E, A]] {
+	return G.Eq[StateReaderIOEither[S, R, E, A]](eqr)
+}
+
+// FromStrictEquals constructs an [EQ.Eq] from the canonical comparison function
+func FromStrictEquals[
+	S, R any, E, A comparable]() func(R) func(S) EQ.Eq[StateReaderIOEither[S, R, E, A]] {
+	return G.FromStrictEquals[StateReaderIOEither[S, R, E, A]]()
+}

statereaderioeither/generic/eq.go

@@ -0,0 +1,49 @@
+// 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 (
+	ET "github.com/IBM/fp-go/either"
+	EQ "github.com/IBM/fp-go/eq"
+	F "github.com/IBM/fp-go/function"
+	P "github.com/IBM/fp-go/pair"
+	G "github.com/IBM/fp-go/readerioeither/generic"
+)
+
+// Eq implements the equals predicate for values contained in the [StateReaderIOEither] monad
+func Eq[
+	SRIOEA ~func(S) RIOEA,
+	RIOEA ~func(R) IOEA,
+	IOEA ~func() ET.Either[E, P.Pair[A, S]],
+	S, R, E, A any](eqr EQ.Eq[RIOEA]) func(S) EQ.Eq[SRIOEA] {
+	return func(s S) EQ.Eq[SRIOEA] {
+		return EQ.FromEquals(func(l, r SRIOEA) bool {
+			return eqr.Equals(l(s), r(s))
+		})
+	}
+}
+
+// FromStrictEquals constructs an [EQ.Eq] from the canonical comparison function
+func FromStrictEquals[
+	SRIOEA ~func(S) RIOEA,
+	RIOEA ~func(R) IOEA,
+	IOEA ~func() ET.Either[E, P.Pair[A, S]],
+	S, R any, E, A comparable]() func(R) func(S) EQ.Eq[SRIOEA] {
+	return F.Flow2(
+		G.FromStrictEquals[RIOEA](),
+		Eq[SRIOEA, RIOEA, IOEA, S, R, E, A],
+	)
+}

statereaderioeither/generic/monad.go

@@ -0,0 +1,159 @@
+// 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 (
+	ET "github.com/IBM/fp-go/either"
+	"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 stateReaderIOEitherPointed[
+	SRIOEA ~func(S) RIOEA,
+	RIOEA ~func(R) IOEA,
+	IOEA ~func() ET.Either[E, P.Pair[A, S]],
+	S, R, E, A any,
+] struct{}
+
+type stateReaderIOEitherFunctor[
+	SRIOEA ~func(S) RIOEA,
+	SRIOEB ~func(S) RIOEB,
+	RIOEA ~func(R) IOEA,
+	RIOEB ~func(R) IOEB,
+	IOEA ~func() ET.Either[E, P.Pair[A, S]],
+	IOEB ~func() ET.Either[E, P.Pair[B, S]],
+	S, R, E, A, B any,
+] struct{}
+
+type stateReaderIOEitherApplicative[
+	SRIOEA ~func(S) RIOEA,
+	SRIOEB ~func(S) RIOEB,
+	SRIOEAB ~func(S) RIOEAB,
+	RIOEA ~func(R) IOEA,
+	RIOEB ~func(R) IOEB,
+	RIOEAB ~func(R) IOEAB,
+	IOEA ~func() ET.Either[E, P.Pair[A, S]],
+	IOEB ~func() ET.Either[E, P.Pair[B, S]],
+	IOEAB ~func() ET.Either[E, P.Pair[func(A) B, S]],
+	S, R, E, A, B any,
+] struct{}
+
+type stateReaderIOEitherMonad[
+	SRIOEA ~func(S) RIOEA,
+	SRIOEB ~func(S) RIOEB,
+	SRIOEAB ~func(S) RIOEAB,
+	RIOEA ~func(R) IOEA,
+	RIOEB ~func(R) IOEB,
+	RIOEAB ~func(R) IOEAB,
+	IOEA ~func() ET.Either[E, P.Pair[A, S]],
+	IOEB ~func() ET.Either[E, P.Pair[B, S]],
+	IOEAB ~func() ET.Either[E, P.Pair[func(A) B, S]],
+	S, R, E, A, B any,
+] struct{}
+
+func (o *stateReaderIOEitherPointed[SRIOEA, RIOEA, IOEA, S, R, E, A]) Of(a A) SRIOEA {
+	return Of[SRIOEA](a)
+}
+
+func (o *stateReaderIOEitherMonad[SRIOEA, SRIOEB, SRIOEAB, RIOEA, RIOEB, RIOEAB, IOEA, IOEB, IOEAB, S, R, E, A, B]) Of(a A) SRIOEA {
+	return Of[SRIOEA](a)
+}
+
+func (o *stateReaderIOEitherApplicative[SRIOEA, SRIOEB, SRIOEAB, RIOEA, RIOEB, RIOEAB, IOEA, IOEB, IOEAB, S, R, E, A, B]) Of(a A) SRIOEA {
+	return Of[SRIOEA](a)
+}
+
+func (o *stateReaderIOEitherMonad[SRIOEA, SRIOEB, SRIOEAB, RIOEA, RIOEB, RIOEAB, IOEA, IOEB, IOEAB, S, R, E, A, B]) Map(f func(A) B) func(SRIOEA) SRIOEB {
+	return Map[SRIOEA, SRIOEB](f)
+}
+
+func (o *stateReaderIOEitherApplicative[SRIOEA, SRIOEB, SRIOEAB, RIOEA, RIOEB, RIOEAB, IOEA, IOEB, IOEAB, S, R, E, A, B]) Map(f func(A) B) func(SRIOEA) SRIOEB {
+	return Map[SRIOEA, SRIOEB](f)
+}
+
+func (o *stateReaderIOEitherFunctor[SRIOEA, SRIOEB, RIOEA, RIOEB, IOEA, IOEB, S, R, E, A, B]) Map(f func(A) B) func(SRIOEA) SRIOEB {
+	return Map[SRIOEA, SRIOEB](f)
+}
+
+func (o *stateReaderIOEitherMonad[SRIOEA, SRIOEB, SRIOEAB, RIOEA, RIOEB, RIOEAB, IOEA, IOEB, IOEAB, S, R, E, A, B]) Chain(f func(A) SRIOEB) func(SRIOEA) SRIOEB {
+	return Chain[SRIOEA, SRIOEB](f)
+}
+
+func (o *stateReaderIOEitherMonad[SRIOEA, SRIOEB, SRIOEAB, RIOEA, RIOEB, RIOEAB, IOEA, IOEB, IOEAB, S, R, E, A, B]) Ap(fa SRIOEA) func(SRIOEAB) SRIOEB {
+	return Ap[SRIOEA, SRIOEB, SRIOEAB, RIOEA, RIOEB, RIOEAB, IOEA, IOEB, IOEAB, S, R, E, A, B](fa)
+}
+
+func (o *stateReaderIOEitherApplicative[SRIOEA, SRIOEB, SRIOEAB, RIOEA, RIOEB, RIOEAB, IOEA, IOEB, IOEAB, S, R, E, A, B]) Ap(fa SRIOEA) func(SRIOEAB) SRIOEB {
+	return Ap[SRIOEA, SRIOEB, SRIOEAB, RIOEA, RIOEB, RIOEAB, IOEA, IOEB, IOEAB, S, R, E, A, B](fa)
+}
+
+// Pointed implements the pointed operations for [StateReaderIOEither]
+func Pointed[
+	SRIOEA ~func(S) RIOEA,
+	RIOEA ~func(R) IOEA,
+	IOEA ~func() ET.Either[E, P.Pair[A, S]],
+	S, R, E, A any,
+]() pointed.Pointed[A, SRIOEA] {
+	return &stateReaderIOEitherPointed[SRIOEA, RIOEA, IOEA, S, R, E, A]{}
+}
+
+// Functor implements the functor operations for [StateReaderIOEither]
+func Functor[
+	SRIOEA ~func(S) RIOEA,
+	SRIOEB ~func(S) RIOEB,
+	RIOEA ~func(R) IOEA,
+	RIOEB ~func(R) IOEB,
+	IOEA ~func() ET.Either[E, P.Pair[A, S]],
+	IOEB ~func() ET.Either[E, P.Pair[B, S]],
+	S, R, E, A, B any,
+]() functor.Functor[A, B, SRIOEA, SRIOEB] {
+	return &stateReaderIOEitherFunctor[SRIOEA, SRIOEB, RIOEA, RIOEB, IOEA, IOEB, S, R, E, A, B]{}
+}
+
+// Applicative implements the applicative operations for [StateReaderIOEither]
+func Applicative[
+	SRIOEA ~func(S) RIOEA,
+	SRIOEB ~func(S) RIOEB,
+	SRIOEAB ~func(S) RIOEAB,
+	RIOEA ~func(R) IOEA,
+	RIOEB ~func(R) IOEB,
+	RIOEAB ~func(R) IOEAB,
+	IOEA ~func() ET.Either[E, P.Pair[A, S]],
+	IOEB ~func() ET.Either[E, P.Pair[B, S]],
+	IOEAB ~func() ET.Either[E, P.Pair[func(A) B, S]],
+	S, R, E, A, B any,
+]() applicative.Applicative[A, B, SRIOEA, SRIOEB, SRIOEAB] {
+	return &stateReaderIOEitherApplicative[SRIOEA, SRIOEB, SRIOEAB, RIOEA, RIOEB, RIOEAB, IOEA, IOEB, IOEAB, S, R, E, A, B]{}
+}
+
+// Monad implements the monadic operations for [StateReaderIOEither]
+func Monad[
+	SRIOEA ~func(S) RIOEA,
+	SRIOEB ~func(S) RIOEB,
+	SRIOEAB ~func(S) RIOEAB,
+	RIOEA ~func(R) IOEA,
+	RIOEB ~func(R) IOEB,
+	RIOEAB ~func(R) IOEAB,
+	IOEA ~func() ET.Either[E, P.Pair[A, S]],
+	IOEB ~func() ET.Either[E, P.Pair[B, S]],
+	IOEAB ~func() ET.Either[E, P.Pair[func(A) B, S]],
+	S, R, E, A, B any,
+]() monad.Monad[A, B, SRIOEA, SRIOEB, SRIOEAB] {
+	return &stateReaderIOEitherMonad[SRIOEA, SRIOEB, SRIOEAB, RIOEA, RIOEB, RIOEAB, IOEA, IOEB, IOEAB, S, R, E, A, B]{}
+}

statereaderioeither/generic/state.go

@@ -104,3 +104,42 @@ func Chain[
 		f,
 	)
 }
+
+func MonadAp[
+	SRIOEA ~func(S) RIOEA,
+	SRIOEB ~func(S) RIOEB,
+	SRIOEAB ~func(S) RIOEAB,
+	RIOEA ~func(R) IOEA,
+	RIOEB ~func(R) IOEB,
+	RIOEAB ~func(R) IOEAB,
+	IOEA ~func() ET.Either[E, P.Pair[A, S]],
+	IOEB ~func() ET.Either[E, P.Pair[B, S]],
+	IOEAB ~func() ET.Either[E, P.Pair[func(A) B, S]],
+	S, R, E, A, B any,
+](fab SRIOEAB, fa SRIOEA) SRIOEB {
+	return ST.MonadAp[SRIOEA, SRIOEB, SRIOEAB](
+		G.MonadMap[RIOEA, RIOEB],
+		G.MonadChain[RIOEAB, RIOEB],
+		fab,
+		fa,
+	)
+}
+
+func Ap[
+	SRIOEA ~func(S) RIOEA,
+	SRIOEB ~func(S) RIOEB,
+	SRIOEAB ~func(S) RIOEAB,
+	RIOEA ~func(R) IOEA,
+	RIOEB ~func(R) IOEB,
+	RIOEAB ~func(R) IOEAB,
+	IOEA ~func() ET.Either[E, P.Pair[A, S]],
+	IOEB ~func() ET.Either[E, P.Pair[B, S]],
+	IOEAB ~func() ET.Either[E, P.Pair[func(A) B, S]],
+	S, R, E, A, B any,
+](fa SRIOEA) func(SRIOEAB) SRIOEB {
+	return ST.Ap[SRIOEA, SRIOEB, SRIOEAB](
+		G.Map[RIOEA, RIOEB],
+		G.Chain[RIOEAB, RIOEB],
+		fa,
+	)
+}

statereaderioeither/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 statereaderioeither
+
+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/statereaderioeither/generic"
+)
+
+// Pointed returns the pointed operations for [StateReaderIOEither]
+func Pointed[S, R, E, A any]() pointed.Pointed[A, StateReaderIOEither[S, R, E, A]] {
+	return G.Pointed[StateReaderIOEither[S, R, E, A]]()
+}
+
+// Functor returns the functor operations for [StateReaderIOEither]
+func Functor[S, R, E, A, B any]() functor.Functor[A, B, StateReaderIOEither[S, R, E, A], StateReaderIOEither[S, R, E, B]] {
+	return G.Functor[StateReaderIOEither[S, R, E, A], StateReaderIOEither[S, R, E, B]]()
+}
+
+// Applicative returns the applicative operations for [StateReaderIOEither]
+func Applicative[S, R, E, A, B any]() applicative.Applicative[A, B, StateReaderIOEither[S, R, E, A], StateReaderIOEither[S, R, E, B], StateReaderIOEither[S, R, E, func(A) B]] {
+	return G.Applicative[StateReaderIOEither[S, R, E, A], StateReaderIOEither[S, R, E, B], StateReaderIOEither[S, R, E, func(A) B]]()
+}
+
+// Monad returns the monadic operations for [StateReaderIOEither]
+func Monad[S, R, E, A, B any]() monad.Monad[A, B, StateReaderIOEither[S, R, E, A], StateReaderIOEither[S, R, E, B], StateReaderIOEither[S, R, E, func(A) B]] {
+	return G.Monad[StateReaderIOEither[S, R, E, A], StateReaderIOEither[S, R, E, B], StateReaderIOEither[S, R, E, func(A) B]]()
+}

statereaderioeither/state.go

@@ -42,3 +42,11 @@ func MonadChain[S, R, E, A, B any](fa StateReaderIOEither[S, R, E, A], f func(A)
 func Chain[S, R, E, A, B any](f func(A) StateReaderIOEither[S, R, E, B]) func(StateReaderIOEither[S, R, E, A]) StateReaderIOEither[S, R, E, B] {
 	return G.Chain[StateReaderIOEither[S, R, E, A], StateReaderIOEither[S, R, E, B]](f)
 }
+
+func MonadAp[S, R, E, A, B any](fab StateReaderIOEither[S, R, E, func(A) B], fa StateReaderIOEither[S, R, E, A]) StateReaderIOEither[S, R, E, B] {
+	return G.MonadAp[StateReaderIOEither[S, R, E, A], StateReaderIOEither[S, R, E, B], StateReaderIOEither[S, R, E, func(A) B]](fab, fa)
+}
+
+func Ap[S, R, E, A, B any](fa StateReaderIOEither[S, R, E, A]) func(StateReaderIOEither[S, R, E, func(A) B]) StateReaderIOEither[S, R, E, B] {
+	return G.Ap[StateReaderIOEither[S, R, E, A], StateReaderIOEither[S, R, E, B], StateReaderIOEither[S, R, E, func(A) B]](fa)
+}

statereaderioeither/testing/laws.go

@@ -0,0 +1,87 @@
+// 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 testing
+
+import (
+	"testing"
+
+	ET "github.com/IBM/fp-go/either"
+	EQ "github.com/IBM/fp-go/eq"
+	L "github.com/IBM/fp-go/internal/monad/testing"
+	P "github.com/IBM/fp-go/pair"
+	RIOE "github.com/IBM/fp-go/readerioeither"
+	ST "github.com/IBM/fp-go/statereaderioeither"
+)
+
+// AssertLaws asserts the apply monad laws for the `Either` monad
+func AssertLaws[S, E, R, A, B, C any](t *testing.T,
+	eqs EQ.Eq[S],
+	eqe EQ.Eq[E],
+	eqa EQ.Eq[A],
+	eqb EQ.Eq[B],
+	eqc EQ.Eq[C],
+
+	ab func(A) B,
+	bc func(B) C,
+
+	s S,
+	r R,
+) func(a A) bool {
+
+	eqra := RIOE.Eq[R](ET.Eq(eqe, P.Eq(eqa, eqs)))(r)
+	eqrb := RIOE.Eq[R](ET.Eq(eqe, P.Eq(eqb, eqs)))(r)
+	eqrc := RIOE.Eq[R](ET.Eq(eqe, P.Eq(eqc, eqs)))(r)
+
+	fofc := ST.Pointed[S, R, E, C]()
+	fofaa := ST.Pointed[S, R, E, func(A) A]()
+	fofbc := ST.Pointed[S, R, E, func(B) C]()
+	fofabb := ST.Pointed[S, R, E, func(func(A) B) B]()
+
+	fmap := ST.Functor[S, R, E, func(B) C, func(func(A) B) func(A) C]()
+
+	fapabb := ST.Applicative[S, R, E, func(A) B, B]()
+	fapabac := ST.Applicative[S, R, E, func(A) B, func(A) C]()
+
+	maa := ST.Monad[S, R, E, A, A]()
+	mab := ST.Monad[S, R, E, A, B]()
+	mac := ST.Monad[S, R, E, A, C]()
+	mbc := ST.Monad[S, R, E, B, C]()
+
+	return L.MonadAssertLaws(t,
+		ST.Eq(eqra)(s),
+		ST.Eq(eqrb)(s),
+		ST.Eq(eqrc)(s),
+
+		fofc,
+		fofaa,
+		fofbc,
+		fofabb,
+
+		fmap,
+
+		fapabb,
+		fapabac,
+
+		maa,
+		mab,
+		mac,
+		mbc,
+
+		ab,
+		bc,
+	)
+
+}

statereaderioeither/testing/laws_test.go

@@ -0,0 +1,51 @@
+// 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 (
+	"context"
+	"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]())
+	eqe := EQ.FromStrictEquals[error]()
+	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, eqe, eqa, eqb, eqc, ab, bc, A.Empty[string](), context.Background())
+
+	assert.True(t, laws(true))
+	assert.True(t, laws(false))
+}