fix: add missing array traversal to either

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

array/array.go

@@ -280,3 +280,11 @@ func IsNonNil[A any](as []A) bool {
 func ConstNil[A any]() []A {
 	return array.ConstNil[[]A]()
 }
+
+func SliceRight[A any](start int) func([]A) []A {
+	return G.SliceRight[[]A](start)
+}
+
+func Copy[A any](b []A) []A {
+	return G.Copy(b)
+}

array/generic/array.go

@@ -180,3 +180,21 @@ func MatchLeft[AS ~[]A, A, B any](onEmpty func() B, onNonEmpty func(A, AS) B) fu
 		return onNonEmpty(as[0], as[1:])
 	}
 }
+
+func Slice[AS ~[]A, A any](start int, end int) func(AS) AS {
+	return func(a AS) AS {
+		return a[start:end]
+	}
+}
+
+func SliceRight[AS ~[]A, A any](start int) func(AS) AS {
+	return func(a AS) AS {
+		return a[start:]
+	}
+}
+
+func Copy[AS ~[]A, A any](b AS) AS {
+	buf := make(AS, len(b))
+	copy(buf, b)
+	return buf
+}

either/array.go

@@ -0,0 +1,46 @@
+// 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 either
+
+import (
+	F "github.com/IBM/fp-go/function"
+	RA "github.com/IBM/fp-go/internal/array"
+)
+
+// TraverseArray transforms an array
+func TraverseArrayG[GA ~[]A, GB ~[]B, E, A, B any](f func(A) Either[E, B]) func(GA) Either[E, GB] {
+	return RA.Traverse[GA](
+		Of[E, GB],
+		Map[E, GB, func(B) GB],
+		Ap[GB, E, B],
+
+		f,
+	)
+}
+
+// TraverseArray transforms an array
+func TraverseArray[E, A, B any](f func(A) Either[E, B]) func([]A) Either[E, []B] {
+	return TraverseArrayG[[]A, []B](f)
+}
+
+func SequenceArrayG[GA ~[]A, GOA ~[]Either[E, A], E, A any](ma GOA) Either[E, GA] {
+	return TraverseArrayG[GOA, GA](F.Identity[Either[E, A]])(ma)
+}
+
+// SequenceArray converts a homogeneous sequence of either into an either of sequence
+func SequenceArray[E, A any](ma []Either[E, A]) Either[E, []A] {
+	return SequenceArrayG[[]A](ma)
+}