fix: refactor Writer monad

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

writer/monad.go

@@ -0,0 +1,45 @@
+// 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 writer
+
+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"
+	M "github.com/IBM/fp-go/monoid"
+	G "github.com/IBM/fp-go/writer/generic"
+)
+
+// Pointed implements the pointed operations for [Writer]
+func Pointed[W, A any](m M.Monoid[W]) pointed.Pointed[A, Writer[W, A]] {
+	return G.Pointed[Writer[W, A], W, A](m)
+}
+
+// Functor implements the pointed operations for [Writer]
+func Functor[W, A, B any]() functor.Functor[A, B, Writer[W, A], Writer[W, B]] {
+	return G.Functor[Writer[W, B], Writer[W, A], W, A, B]()
+}
+
+// Applicative implements the applicative operations for [Writer]
+func Applicative[W, A, B any](m M.Monoid[W]) applicative.Applicative[A, B, Writer[W, A], Writer[W, B], Writer[W, func(A) B]] {
+	return G.Applicative[Writer[W, B], Writer[W, func(A) B], Writer[W, A]](m)
+}
+
+// Monad implements the monadic operations for [Writer]
+func Monad[W, A, B any](m M.Monoid[W]) monad.Monad[A, B, Writer[W, A], Writer[W, B], Writer[W, func(A) B]] {
+	return G.Monad[Writer[W, B], Writer[W, func(A) B], Writer[W, A]](m)
+}