fix: use endomorphism

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

endomorphism/generic/monoid.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 generic
+
+import (
+	F "github.com/IBM/fp-go/function"
+	M "github.com/IBM/fp-go/monoid"
+	S "github.com/IBM/fp-go/semigroup"
+)
+
+// Of converts any function to an [Endomorphism]
+func Of[ENDO ~func(A) A, F ~func(A) A, A any](f F) ENDO {
+	return func(a A) A {
+		return f(a)
+	}
+}
+
+func Identity[ENDO ~func(A) A, A any]() ENDO {
+	return func(a A) A {
+		return a
+	}
+}
+
+func Compose[ENDO ~func(A) A, A any](f1, f2 ENDO) ENDO {
+	return func(a A) A {
+		return F.Pipe2(a, f1, f2)
+	}
+}
+
+// Semigroup for the Endomorphism where the `concat` operation is the usual function composition.
+func Semigroup[ENDO ~func(A) A, A any]() S.Semigroup[ENDO] {
+	return S.MakeSemigroup(Compose[ENDO])
+}
+
+// Monoid for the Endomorphism where the `concat` operation is the usual function composition.
+func Monoid[ENDO ~func(A) A, A any]() M.Monoid[ENDO] {
+	return M.MakeMonoid(Compose[ENDO], Identity[ENDO]())
+}

endomorphism/monoid.go

@@ -16,17 +16,30 @@
 package endomorphism
 
 import (
-	F "github.com/IBM/fp-go/function"
+	G "github.com/IBM/fp-go/endomorphism/generic"
 	M "github.com/IBM/fp-go/monoid"
 	S "github.com/IBM/fp-go/semigroup"
 )
 
+// Endomorphism is a function  that
+type Endomorphism[A any] func(A) A
+
+// Of converts any function to an [Endomorphism]
+func Of[F ~func(A) A, A any](f F) Endomorphism[A] {
+	return G.Of[Endomorphism[A]](f)
+}
+
+// Identity returns the identity [Endomorphism]
+func Identity[A any]() Endomorphism[A] {
+	return G.Identity[Endomorphism[A]]()
+}
+
 // Semigroup for the Endomorphism where the `concat` operation is the usual function composition.
-func Semigroup[A any]() S.Semigroup[func(A) A] {
-	return S.MakeSemigroup(F.Flow2[func(A) A, func(A) A])
+func Semigroup[A any]() S.Semigroup[Endomorphism[A]] {
+	return G.Semigroup[Endomorphism[A]]()
 }
 
 // Monoid for the Endomorphism where the `concat` operation is the usual function composition.
-func Monoid[A any]() M.Monoid[func(A) A] {
-	return M.MakeMonoid(F.Flow2[func(A) A, func(A) A], F.Identity[A])
+func Monoid[A any]() M.Monoid[Endomorphism[A]] {
+	return G.Monoid[Endomorphism[A]]()
 }