curry.js

/**
 * A JavaScript utility for function currying. Inspired by Haskell's built-in
 * currying feature. Example:
 *
 *   var adder = curry(function (a, b, c) {
 *       return a + b + c;
 *   });
 *
 *   var add_10 = adder(10);
 *   var add_20 = add_10(10);
 *
 *   print(add_20(10)); // prints 30
 *
 * @see     http://en.wikipedia.org/wiki/Currying
 * @author  Ionut G. Stan <ionut.g.stan ~ gmail.com>
 * @license BSD
 */
var curry = function (f) {
    var array     = Array.slice,
        prevArity = arguments[1] || f.length;

    return function () {
        var args      = array(arguments),
            currArity = args.length;

        if (currArity >= prevArity) {
            return f.apply(this, args);
        }

        return curry(function () {
            return f.apply(this, args.concat(array(arguments)));
        }, prevArity - currArity);
    };
};

/**
 * Specs using the jSpec library.
 *
 * @see http://github.com/igstan/jSpec/tree/master
 */
if (typeof jSpec !== "undefined") {

    $.describe("The curry() function", function () {
        $.it("should curry one argument functions", function () {
            var unary = curry(function (a) {
                return a;
            });

            var result = unary(1);

            $(result).should.equal(1);
        });

        $.it("should curry multi argument functions", function () {
            var nary = curry(function (a, b) {
                return a + b;
            });

            var result = nary(1)(2);

            $(result).should.equal(3);
        });

        $.it("should curry multi argument functions", function () {
            var nary = curry(function (a, b, c) {
                return a + b + c;
            });
            
            var result = nary(1, 2)(3);

            $(result).should.equal(6);
        });
    });

}