JavaScript- The Good Parts function Curry

Functions are values, and we can manipulate function values in interesting ways.Currying allows us to produce a new function by combining a function and an argument:

var add1 = add.curry(1);
document.writeln(add1(6));    // 7

add1 is a function that was created by passing 1 to add’s curry method. The add1 function adds 1 to its argument. JavaScript does not have a curry method, but we can fix that by augmenting Function.prototype:

Function.method(‘curry‘, function ( ) {
    var args = arguments, that = this;
    return function ( ) {
        return that.apply(null, args.concat(arguments));
    };
});    // Something isn‘t right...

The curry method works by creating a closure that holds that original function and the arguments to curry. It returns a function that, when invoked, returns the result of calling that original function, passing it all of the arguments from the invocation of curry and the current invocation. It uses the Array concat method to concatenate the two arrays of arguments together.

Unfortunately, as we saw earlier, the arguments array is not an array, so it does not have the concat method. To work around that, we will apply the array slice method on both of the arguments arrays. This produces arrays that behave correctly with the concat method:

Function.method(‘curry‘, function ( ) {
    var slice = Array.prototype.slice,
        args = slice.apply(arguments),
        that = this;
    return function ( ) {
        return that.apply(null, args.concat(slice.apply(arguments)));
    };
});

我想给所有的函数对象都添加curry方法：

function add(){
    console.log(arguments);
}
add.curry();

运行结果：

> add.curry();
TypeError: Object function add(){
console.log(‘add‘);
} has no method ‘curry‘
    at repl:1:5
    at REPLServer.self.eval (repl.js:110:21)
    at repl.js:249:20
    at REPLServer.self.eval (repl.js:122:7)
    at Interface.<anonymous> (repl.js:239:12)
    at Interface.emit (events.js:95:17)
    at Interface._onLine (readline.js:202:10)
    at Interface._line (readline.js:531:8)
    at Interface._ttyWrite (readline.js:760:14)
    at ReadStream.onkeypress (readline.js:99:10)

其实add是一个函数对象，所有的函数都是Function的对象，它继承了Function.prototype：

Function.prototype[‘curry‘] = function ( ) {
    var slice = Array.prototype.slice,
        args = slice.apply(arguments),
        that = this;
    return function ( ) {
        return that.apply(null, args.concat(slice.apply(arguments)));
    };
}

现在所有的方法对象都会有curry方法了：

> add2 = add.curry(1)
[Function]
> add2(2,3)
{ ‘0‘: 1, ‘1‘: 2, ‘2‘: 3 }
undefined
> add2(2,3,4)
{ ‘0‘: 1, ‘1‘: 2, ‘2‘: 3, ‘3‘: 4 }
undefined