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62 lines
1.7 KiB
Go
62 lines
1.7 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 semigroup
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import (
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F "github.com/IBM/fp-go/function"
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M "github.com/IBM/fp-go/magma"
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)
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type Semigroup[A any] interface {
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M.Magma[A]
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}
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type semigroup[A any] struct {
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c func(A, A) A
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}
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func (self semigroup[A]) Concat(x A, y A) A {
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return self.c(x, y)
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}
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func MakeSemigroup[A any](c func(A, A) A) Semigroup[A] {
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return semigroup[A]{c: c}
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}
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// Reverse returns The dual of a `Semigroup`, obtained by swapping the arguments of `concat`.
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func Reverse[A any](m Semigroup[A]) Semigroup[A] {
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return MakeSemigroup(M.Reverse[A](m).Concat)
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}
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// FunctionSemigroup forms a semigroup as long as you can provide a semigroup for the codomain.
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func FunctionSemigroup[A, B any](S Semigroup[B]) Semigroup[func(A) B] {
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return MakeSemigroup(func(f func(A) B, g func(A) B) func(A) B {
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return func(a A) B {
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return S.Concat(f(a), g(a))
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}
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})
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}
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// First always returns the first argument.
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func First[A any]() Semigroup[A] {
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return MakeSemigroup(F.First[A, A])
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}
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// Last always returns the last argument.
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func Last[A any]() Semigroup[A] {
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return MakeSemigroup(F.Second[A, A])
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}
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