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102 lines
2.7 KiB
Go
102 lines
2.7 KiB
Go
// Copyright (c) 2023 IBM Corp.
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// All rights reserved.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package either
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import (
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"fmt"
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)
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type (
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either struct {
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isLeft bool
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value any
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}
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// Either defines a data structure that logically holds either an E or an A. The flag discriminates the cases
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Either[E, A any] either
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)
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// String prints some debug info for the object
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//
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// go:noinline
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func eitherString(s *either) string {
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if s.isLeft {
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return fmt.Sprintf("Left[%T](%v)", s.value, s.value)
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}
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return fmt.Sprintf("Right[%T](%v)", s.value, s.value)
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}
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// Format prints some debug info for the object
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//
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// go:noinline
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func eitherFormat(e *either, f fmt.State, c rune) {
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switch c {
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case 's':
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fmt.Fprint(f, eitherString(e))
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default:
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fmt.Fprint(f, eitherString(e))
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}
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}
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// String prints some debug info for the object
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func (s Either[E, A]) String() string {
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return eitherString((*either)(&s))
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}
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// Format prints some debug info for the object
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func (s Either[E, A]) Format(f fmt.State, c rune) {
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eitherFormat((*either)(&s), f, c)
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}
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// IsLeft tests if the [Either] is a left value. Rather use [Fold] if you need to access the values. Inverse is [IsRight].
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func IsLeft[E, A any](val Either[E, A]) bool {
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return val.isLeft
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}
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// IsLeft tests if the [Either] is a right value. Rather use [Fold] if you need to access the values. Inverse is [IsLeft].
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func IsRight[E, A any](val Either[E, A]) bool {
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return !val.isLeft
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}
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// Left creates a new instance of an [Either] representing the left value.
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func Left[A, E any](value E) Either[E, A] {
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return Either[E, A]{true, value}
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}
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// Right creates a new instance of an [Either] representing the right value.
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func Right[E, A any](value A) Either[E, A] {
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return Either[E, A]{false, value}
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}
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// MonadFold extracts the values from an [Either] by invoking the [onLeft] callback or the [onRight] callback depending on the case
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func MonadFold[E, A, B any](ma Either[E, A], onLeft func(e E) B, onRight func(a A) B) B {
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if ma.isLeft {
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return onLeft(ma.value.(E))
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}
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return onRight(ma.value.(A))
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}
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// Unwrap converts an [Either] into the idiomatic tuple
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func Unwrap[E, A any](ma Either[E, A]) (A, E) {
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if ma.isLeft {
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var a A
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return a, ma.value.(E)
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} else {
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var e E
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return ma.value.(A), e
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}
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}
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