fix: add optics and consistent copyright

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

optics/lens/generic/lens.go

@@ -0,0 +1,35 @@
+// 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 (
+	L "github.com/IBM/fp-go/optics/lens"
+)
+
+// AsTraversal converts a lens to a traversal
+func AsTraversal[R ~func(func(A) HKTA) func(S) HKTS, S, A, HKTS, HKTA any](
+	fmap func(HKTA, func(A) S) HKTS,
+) func(L.Lens[S, A]) R {
+	return func(sa L.Lens[S, A]) R {
+		return func(f func(a A) HKTA) func(S) HKTS {
+			return func(s S) HKTS {
+				return fmap(f(sa.Get(s)), func(a A) S {
+					return sa.Set(a)(s)
+				})
+			}
+		}
+	}
+}