fix: add missing withIndex methods

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

ioeither/traverse_test.go

@@ -0,0 +1,37 @@
+// 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 ioeither
+
+import (
+	"fmt"
+	"testing"
+
+	A "github.com/IBM/fp-go/array"
+	E "github.com/IBM/fp-go/either"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestTraverseArray(t *testing.T) {
+
+	src := A.From("A", "B")
+
+	trfrm := TraverseArrayWithIndex(func(idx int, data string) IOEither[error, string] {
+		return Of[error](fmt.Sprintf("idx: %d, data: %s", idx, data))
+	})
+
+	assert.Equal(t, E.Of[error](A.From("idx: 0, data: A", "idx: 1, data: B")), trfrm(src)())
+
+}