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54 lines
1.7 KiB
Go
54 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 option
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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/monoid"
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S "github.com/IBM/fp-go/semigroup"
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)
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func Semigroup[A any]() func(S.Semigroup[A]) S.Semigroup[Option[A]] {
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return func(s S.Semigroup[A]) S.Semigroup[Option[A]] {
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concat := s.Concat
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return S.MakeSemigroup(
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func(x, y Option[A]) Option[A] {
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return MonadFold(x, F.Constant(y), func(left A) Option[A] {
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return MonadFold(y, F.Constant(x), func(right A) Option[A] {
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return Some(concat(left, right))
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})
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})
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},
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)
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}
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}
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// Monoid returning the left-most non-`None` value. If both operands are `Some`s then the inner values are
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// concatenated using the provided `Semigroup`
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//
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// | x | y | concat(x, y) |
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// | ------- | ------- | ------------------ |
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// | none | none | none |
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// | some(a) | none | some(a) |
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// | none | some(b) | some(b) |
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// | some(a) | some(b) | some(concat(a, b)) |
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func Monoid[A any]() func(S.Semigroup[A]) M.Monoid[Option[A]] {
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sg := Semigroup[A]()
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return func(s S.Semigroup[A]) M.Monoid[Option[A]] {
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return M.MakeMonoid(sg(s).Concat, None[A]())
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}
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}
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