fix: introduce stateless iterator

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

iterator/stateless/iterator_test.go

@@ -0,0 +1,60 @@
+// 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 stateless
+
+import (
+	"fmt"
+	"testing"
+
+	A "github.com/IBM/fp-go/array"
+	F "github.com/IBM/fp-go/function"
+	"github.com/IBM/fp-go/internal/utils"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestIterator(t *testing.T) {
+
+	result := F.Pipe2(
+		A.From(1, 2, 3),
+		FromArray[int],
+		Reduce(utils.Sum, 0),
+	)
+
+	assert.Equal(t, 6, result)
+}
+
+func TestChain(t *testing.T) {
+
+	outer := FromArray[int](A.From(1, 2, 3))
+
+	inner := func(data int) Iterator[string] {
+		return F.Pipe2(
+			A.From(0, 1),
+			FromArray[int],
+			Map(func(idx int) string {
+				return fmt.Sprintf("item[%d][%d]", data, idx)
+			}),
+		)
+	}
+
+	total := F.Pipe2(
+		outer,
+		Chain(inner),
+		ToArray[string],
+	)
+
+	assert.Equal(t, A.From("item[1][0]", "item[1][1]", "item[2][0]", "item[2][1]", "item[3][0]", "item[3][1]"), total)
+}