回答編集履歴
4
シンタックスハイライトの言語の変更
test
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@@ -50,98 +50,98 @@
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```lang-Kotlin
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abstract class Maybe<T>
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{
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public sealed class Just (T value) : Maybe<T> {}
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public sealed class Nothing : Maybe<T> {}
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}
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```
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これを先のトレートのインスタンスにしていきます。
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```lang-C#
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instance Functor<Maybe<_>>
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{
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{
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Maybe<S> Map<T, S>(Func<T, S> f, Maybe<T> ma) =>
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ma switch {
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Maybe<T>.Just (var a) => new Maybe<S>.Just(f(a)),
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Maybe<T>.Nothing => new Maybe<S>.Nothing()
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};
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}
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}
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instance Applicative<Maybe<_>>
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{
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Maybe<S> App<T, S>(Maybe<Func<T, S>> mf, Maybe<T> ma) =>
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(mf, ma) switch {
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(Maybe<Func<T, S>>.Just (var f), Maybe<T>.Just (var a)) => new Maybe<S>.Just(f(a)),
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(Maybe<Func<T, S>>.Nothing, _) => new Maybe<S>.Nothing(),
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(_, Maybe<T>.Nothing) => new Maybe<S>.Nothing()
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};
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Maybe<T> Pure<T>(T a) => new Maybe<T>.Just(a);
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}
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instance Monad<Maybe<_>>
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{
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Maybe<S> Bind<T, S>(Maybe<T> ma, Func<T, Maybe<S>> f) =>
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ma switch {
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Maybe<T>.Just (var a) => f(a),
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Maybe<T>.Nothing => Maybe<S>.Nothing
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};
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}
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```
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```
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こ
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使用する場合はこのようなコードを想定しています。
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```lang-C#
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instance Functor<Maybe<_>>
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{
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Maybe<S> Map<T, S>(Func<T, S> f, Maybe<T> ma) =>
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ma switch {
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Maybe<T>.Just (var a) => new Maybe<S>.Just(f(a)),
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Maybe<T>.Nothing => new Maybe<S>.Nothing()
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};
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}
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instance Applicative<Maybe<_>>
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{
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Maybe<S> App<T, S>(Maybe<Func<T, S>> mf, Maybe<T> ma) =>
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(mf, ma) switch {
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(Maybe<Func<T, S>>.Just (var f), Maybe<T>.Just (var a)) => new Maybe<S>.Just(f(a)),
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(Maybe<Func<T, S>>.Nothing, _) => new Maybe<S>.Nothing(),
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(_, Maybe<T>.Nothing) => new Maybe<S>.Nothing()
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};
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Maybe<T> Pure<T>(T a) => new Maybe<T>.Just(a);
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}
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instance Monad<Maybe<_>>
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{
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Maybe<S> Bind<T, S>(Maybe<T> ma, Func<T, Maybe<S>> f) =>
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ma switch {
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Maybe<T>.Just (var a) => f(a),
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Maybe<T>.Nothing => Maybe<S>.Nothing
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};
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}
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```
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使用する場合はこのようなコードを想定しています。
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```lang-C#
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/// 名前から関数を探す関数
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/// 見付からなければ Nothing
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3
コード修正
test
CHANGED
@@ -38,7 +38,7 @@
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{
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F<S> Bind<T, S>(F<T> a, Func<T, F<S>> f);
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}
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Maybe<S> Map<T, S>(Func<T, S> f, Maybe<T> ma) =>
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a switch {
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ma switch {
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Maybe<T>.Just (var a) => new Maybe<S>.Just(f(a)),
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2
F の具体化忘れ
test
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@@ -110,7 +110,7 @@
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Maybe<T> Pure<T>(T a) => new Maybe<T>.Just(a);
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}
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コメント修正
test
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@@ -184,7 +184,7 @@
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// ユーザーの入力が整数値でなければ Nothing
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// それ以外ならば、ユーザーの入力が 10 とすると "-10" という文字列
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// それ以外ならば、ユーザーの入力が 10 とすると "-10" という文字列が Just に包まれたもの
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