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