Currying in js

curry.js

var DEBUG = false;

var debug = function(msg) {
    if (DEBUG) {
        console.log(msg);
    }
}

Function.prototype.curry = function() {
    this.argList || (this.argList = []);

    var newArgList = this.argList.concat(Array.prototype.slice.call(arguments, 0));
    var len = (this.len || this.length);
    debug("arguments: " + newArgList + " ; len: " + len);

    if (newArgList.length >= len) {
        debug("apply");
        return this.apply(null, newArgList);
    }

    var self = this;
    var fun = function() {        
        var res = self.apply(self, arguments);
        debug("accessible len: " + len);
        if (res.curry) {
            debug("result is a function");
            var newArgs = Array.prototype.slice.call(arguments, len);
            debug("new arguments: " + newArgs);
            return res.curry.apply(res, newArgs);
        }
        debug("result is a scalar");

        return res;
    };
    fun.len = len;
    fun.argList = newArgList;

    return fun;
}

var c = (x, y) => x; // Haskell: const = \x, y => x
var id = x => x      // Haskell: id = \x => x

var snd = c.curry(id); // Haskell: snd = const id    -- const id = (\x.\y.x) (\x.x) = \y.(\x.x) = \y.\x.x

// Example 1
var f = snd.curry(1);  // Haskell: f = snd 1  -- const id 1 = \y.\x.x 1 = \x.x = id
f.curry(3); // = f(3) = 3

// Example 2
snd.curry(1, 2);  // = 2; Haskell: snd 1 2 = const id 1 2 = \y.\x.x 1 2 = \x.x 2 = 2