fp-go/v2/either/semigroup.go

// Copyright (c) 2023 - 2025 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 (
	S "github.com/IBM/fp-go/v2/semigroup"
)

// AltSemigroup creates a semigroup for Either that uses the Alt operation for combining values.
// When combining two Either values, it returns the first Right value, or the second value if the first is Left.
//
// Example:
//
//	sg := either.AltSemigroup[error, int]()
//	result := sg.Concat(either.Left[int](errors.New("error")), either.Right[error](42))
//	// result is Right(42)
//	result2 := sg.Concat(either.Right[error](1), either.Right[error](2))
//	// result2 is Right(1) - first Right wins
func AltSemigroup[E, A any]() S.Semigroup[Either[E, A]] {
	return S.AltSemigroup(
		MonadAlt[E, A],
	)
}