fix: add optics and consistent copyright

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

optics/traversal/generic/traversal.go

@@ -0,0 +1,73 @@
+// 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 (
+	AR "github.com/IBM/fp-go/array/generic"
+	C "github.com/IBM/fp-go/constant"
+	F "github.com/IBM/fp-go/function"
+)
+
+type (
+	Traversal[S, A, HKTS, HKTA any] func(func(A) HKTA) func(S) HKTS
+)
+
+func Compose[
+	TAB ~func(func(B) HKTB) func(A) HKTA,
+	TSA ~func(func(A) HKTA) func(S) HKTS,
+	TSB ~func(func(B) HKTB) func(S) HKTS,
+	S, A, B, HKTS, HKTA, HKTB any](ab TAB) func(TSA) TSB {
+	return func(sa TSA) TSB {
+		return F.Flow2(ab, sa)
+	}
+}
+
+func FromTraversable[
+	TAB ~func(func(A) HKTFA) func(HKTTA) HKTAA,
+	A,
+	HKTTA,
+	HKTFA,
+	HKTAA any](
+	traverseF func(HKTTA, func(A) HKTFA) HKTAA,
+) TAB {
+	return F.Bind1st(F.Bind2nd[HKTTA, func(A) HKTFA, HKTAA], traverseF)
+}
+
+// FoldMap maps each target to a `Monoid` and combines the result
+func FoldMap[M, S, A any](f func(A) M) func(sa Traversal[S, A, C.Const[M, S], C.Const[M, A]]) func(S) M {
+	return func(sa Traversal[S, A, C.Const[M, S], C.Const[M, A]]) func(S) M {
+		return F.Flow2(
+			F.Pipe1(
+				F.Flow2(f, C.Make[M, A]),
+				sa,
+			),
+			C.Unwrap[M, S],
+		)
+	}
+}
+
+// Fold maps each target to a `Monoid` and combines the result
+func Fold[S, A any](sa Traversal[S, A, C.Const[A, S], C.Const[A, A]]) func(S) A {
+	return FoldMap[A, S, A](F.Identity[A])(sa)
+}
+
+// GetAll gets all the targets of a traversal
+func GetAll[GA ~[]A, S, A any](s S) func(sa Traversal[S, A, C.Const[GA, S], C.Const[GA, A]]) GA {
+	fmap := FoldMap[GA, S, A](AR.Of[GA, A])
+	return func(sa Traversal[S, A, C.Const[GA, S], C.Const[GA, A]]) GA {
+		return fmap(sa)(s)
+	}
+}