Curry functions in Javascript with variable argument lengths

curry.js

function toArray(args) {
  return [].slice.call(args);
}

function sub_curry(fn /*, variable number of args */) {
  var args = [].slice.call(arguments, 1);
  return function () {
    return fn.apply(this, args.concat(toArray(arguments)));
  };
}

function curry(fn, length) {
  // capture fn's # of parameters
  length = length || fn.length;
  return function () {
    if (arguments.length < length) {
      // not all arguments have been specified. Curry once more.
      var combined = [fn].concat(toArray(arguments));
      return length - arguments.length > 0 
        ? curry(sub_curry.apply(this, combined), length - arguments.length)
        : sub_curry.call(this, combined );
    } else {
      // all arguments have been specified, actually call function
      return fn.apply(this, arguments);
    }
  };
}

var fn = curry(function(a, b, c) { return [a, b, c]; });

// these are all equivalent
fn("a", "b", "c");
fn("a", "b")("c");
fn("a")("b", "c");
fn("a")("b")("c");
//=> ["a", "b", "c"]