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JSでデフォルトカリー化

6
Last updated at Posted at 2016-11-15

JS(ES2015)でデフォルトカリー化を味わうためには、関数定義は以下のようにするものだ、と自分に言いきかせます。

func = arg1 => arg2 => .. 関数本体

たとえば、以下のように関数を定義して…

func = x => y => z => x+y+z;

呼び出しは以下のようにします。

console.log(func(3)(4)(5)); // ==> 12

これでOK。
え?呼び出しが煩雑だって?
ならば、以下のように$プロパティをFunctionに定義すると…

uncurry = (func) => {
    return new Proxy(func,
                     {
                         apply(target, thisArg, argsList) {
                             return argsList.reduce((last, arg)=>{
                                 return last.call(thisArg, arg);
                             }, target);
                         }
                     }
                    );
};


Object.defineProperty(Function.prototype, "$", {
    get: function() {return uncurry(this); },
});

こんな風にできます。

console.log(func.$(3,4,5)); // ==> 12 
console.log(func(3).$(4,5)); // ==> 12 
console.log(func(3)(4).$(5)); // ==> 12 
console.log(func.$(3,4)(5)); // ==> 12

$はhaskellの$のイメージ。

追記

NPMパッケージ化しました。

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