fix_underscore.js

// add methods ending in 'f' to flip first two args
 
_.extend(_,_.reduce(_.keys(_),function(m,k){m[k+'f']=function(a,b){return _[k](b,a)};return m},{}));
 
// add a 'flip' property to functions (loses context if important):
 
Function.prototype.flip = function() {
  var args = [].slice.apply(arguments);
  var tmp = args[0]; args[0] = args[1]; args[1] = args[0];
  return this.apply(this, args);
}
 
// usage: _.each.flip(myFn, [1,2,3])
 
// partial application with placeholder:
 
var partial = function(fn) {
  var savedArgs = [].slice.call(arguments,1);
  return function() {
    var applyArgs = [].slice.call(arguments);
    var args = [];
    for (var i = 0; i < savedArgs.length + arguments.length; i++) {
      args[i] = savedArgs[i] !== partial._ ? savedArgs[i] : applyArgs.shift();
    }
    return fn.apply(this, args.concat(applyArgs));
  };
};
partial._={};

// usage:

var eachMyFn = patial(_.each, partial._, myFn);