Functional mixins for Underscore

underscore-functional.js

_.mixin({
  flipAll: function(f) {
    return function() {
      var args = Array.prototype.slice.call(arguments).reverse();
      return f.apply(this, args);
    };
  },
  flip: function(f) {
    return function() {
      var args = Array.prototype.slice.call(arguments),
          t = args[0];
      args[0] = args[1];
      args[1] = t;
      return f.apply(this, args);
    };
  }
});

// divide = function(a, b) { return a / b }
// divide(6, 3)
// -> 2
// _.flip(divide)(6, 3)
// -> 0.5

// divideByTwo = _.partial(_.flip(divide), 2)
// divideByTwo(6)
// -> 3