fix: introduce stateless iterator

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

context/readerioeither/cancel.go

@@ -19,7 +19,7 @@ import (
 	G "github.com/IBM/fp-go/context/readerioeither/generic"
 )
 
-// WithContext wraps an existing ReaderIOEither and performs a context check for cancellation before delegating
+// WithContext wraps an existing [ReaderIOEither] and performs a context check for cancellation before delegating
 func WithContext[A any](ma ReaderIOEither[A]) ReaderIOEither[A] {
 	return G.WithContext(ma)
 }

context/readerioeither/data/file.txt

@@ -0,0 +1 @@
+Carsten

context/readerioeither/eq.go

@@ -23,7 +23,7 @@ import (
 	EQ "github.com/IBM/fp-go/eq"
 )
 
-// Eq implements the equals predicate for values contained in the IOEither monad
+// Eq implements the equals predicate for values contained in the [ReaderIOEither] monad
 func Eq[A any](eq EQ.Eq[ET.Either[error, A]]) func(context.Context) EQ.Eq[ReaderIOEither[A]] {
 	return G.Eq[ReaderIOEither[A]](eq)
 }

context/readerioeither/file/file.go

@@ -48,7 +48,7 @@ func Close[C io.Closer](c C) RIOE.ReaderIOEither[any] {
 
 // ReadFile reads a file in the scope of a context
 func ReadFile(path string) RIOE.ReaderIOEither[[]byte] {
-	return RIOE.WithResource[*os.File, []byte](Open(path), Close[*os.File])(func(r *os.File) RIOE.ReaderIOEither[[]byte] {
+	return RIOE.WithResource[[]byte](Open(path), Close[*os.File])(func(r *os.File) RIOE.ReaderIOEither[[]byte] {
 		return func(ctx context.Context) IOE.IOEither[error, []byte] {
 			return IOE.MakeIO(func() ET.Either[error, []byte] {
 				return file.ReadAll(ctx, r)

context/readerioeither/resource.go

@@ -20,7 +20,7 @@ import (
 )
 
 // WithResource constructs a function that creates a resource, then operates on it and then releases the resource
-func WithResource[R, A, ANY any](onCreate ReaderIOEither[R], onRelease func(R) ReaderIOEither[ANY]) func(func(R) ReaderIOEither[A]) ReaderIOEither[A] {
+func WithResource[A, R, ANY any](onCreate ReaderIOEither[R], onRelease func(R) ReaderIOEither[ANY]) func(func(R) ReaderIOEither[A]) ReaderIOEither[A] {
 	// wraps the callback functions with a context check
 	return G.WithResource[ReaderIOEither[A]](onCreate, onRelease)
 }

context/readerioeither/resource_test.go

@@ -0,0 +1,79 @@
+// 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 readerioeither
+
+import (
+	"context"
+	"io"
+	"os"
+
+	B "github.com/IBM/fp-go/bytes"
+	F "github.com/IBM/fp-go/function"
+	IO "github.com/IBM/fp-go/io"
+	IOE "github.com/IBM/fp-go/ioeither"
+)
+
+var (
+	openFile = F.Flow3(
+		IOE.Eitherize1(os.Open),
+		FromIOEither[*os.File],
+		ChainFirstIOK(F.Flow2(
+			(*os.File).Name,
+			IO.Logf[string]("Opened file [%s]"),
+		)),
+	)
+)
+
+func closeFile(f *os.File) ReaderIOEither[string] {
+	return F.Pipe1(
+		TryCatch(func(_ context.Context) func() (string, error) {
+			return func() (string, error) {
+				return f.Name(), f.Close()
+			}
+		}),
+		ChainFirstIOK(IO.Logf[string]("Closed file [%s]")),
+	)
+}
+
+func ExampleWithResource() {
+
+	stringReader := WithResource[string](openFile("data/file.txt"), closeFile)
+
+	rdr := stringReader(func(f *os.File) ReaderIOEither[string] {
+		return F.Pipe2(
+			TryCatch(func(_ context.Context) func() ([]byte, error) {
+				return func() ([]byte, error) {
+					return io.ReadAll(f)
+				}
+			}),
+			ChainFirstIOK(F.Flow2(
+				B.Size,
+				IO.Logf[int]("Read content of length [%d]"),
+			)),
+			Map(B.ToString),
+		)
+	})
+
+	contentIOE := F.Pipe2(
+		context.Background(),
+		rdr,
+		IOE.ChainFirstIOK[error](IO.Printf[string]("Content: %s")),
+	)
+
+	contentIOE()
+
+	// Output: Content: Carsten
+}

context/readerioeither/type.go

@@ -21,5 +21,6 @@ import (
 	RE "github.com/IBM/fp-go/readerioeither"
 )
 
-// ReaderIOEither is a specialization of the Reader monad for the typical golang scenario
+// ReaderIOEither is a specialization of the [RE.ReaderIOEither] monad for the typical golang scenario in which the
+// left value is an [error] and the context is a [context.Context]
 type ReaderIOEither[A any] RE.ReaderIOEither[context.Context, error, A]