Some building blocks for functional programming in Javascript

functional.js

function curry(fn) {
  var arity = fn.length,
      args = Array.prototype.slice.call(arguments, 1);

  function accumulator() {
    var leftArgs = args.concat(Array.prototype.slice.call(arguments, 0));

    if (leftArgs.length >= arity) {
      return fn.apply(this, leftArgs);
    } else {
      return curry.apply(this, [fn].concat(leftArgs));
    }
  }

  return args.length >= arity ? accumulator() : accumulator;
}

function compose() {
  var fns = Array.prototype.slice.call(arguments);

  return fns.reduce(function(f, g) {
    return function() {
      return f(g.apply(this, arguments));
    }
  });
}

tests.js

var assert = console.assert;

var sum = function(a, b, c) { return a + b + c }
var curriedSum = curry(sum);

assert(sum(1, 2, 3) == curriedSum(1)(2)(3), "Curring all arguments");
assert(sum(1, 2, 3) == curriedSum(1, 2)(3), "Curring half arguments");
assert(sum(1, 2, 3) == curriedSum(1, 2, 3), "No curring");

var downcase = function(string) { return string.toLowerCase() }
var removeNumbers = function(string) { return string.replace(/\d/g, "") }
var removeSpaces = function(string) { return string.replace(/\s/g, "") }

var name = "R0Dr1G0 N4V4rR0";
assert(compose(downcase, removeNumbers, removeSpaces)(name) == "rdrgnvrr", "Composing three function")