Function currying in JavaScript with blank variable support.

partial-function-applications.js

Function.prototype.__ = {};

Function.prototype.curry = function () {

  var fn = this,
      args = Array.prototype.slice.call(arguments, 0);

  while(args.length < fn.length) {
    args.push(Function.prototype.__);
  }

  var supplied = args.filter(function(v) {
    return Function.prototype.__ !== v;
  });

  if (supplied.length === fn.length) {
    return fn.apply(this, supplied);
  }

  return function () {
    var anonArgs = Array.prototype.slice.call(arguments, 0);
    var newArgs = args.map(function(a) {
      return (a === Function.prototype.__ && anonArgs.length > 0) ? anonArgs.shift() : a;
    });
    return Function.prototype.curry.apply(fn, newArgs);
  };
};

/** Meanwhile in user-land... **/

var __ = Function.prototype.__;

var argsInspect = function (a, b, c, d) {
  console.log([a, b, c, d]);
}

var a = argsInspect.curry(__, 2, __, 4);
a(1)(3); // [1, 2, 3, 4]