fix: add optics and consistent copyright

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

endomorphism/monoid.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 endomorphism
+
+import (
+	F "github.com/IBM/fp-go/function"
+	M "github.com/IBM/fp-go/monoid"
+	S "github.com/IBM/fp-go/semigroup"
+)
+
+func concat[A any](first, second func(A) A) func(A) A {
+	return F.Flow2(first, second)
+}
+
+// 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(concat[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(concat[A], F.Identity[A])
+}