The examples here are taken from Function page of the Prototype JS api documentation. They have been re-written to reflect the Prototype XUL changes. Hope they help!

argumentNames

var fn = function(foo, bar) {
   return foo + bar;
};

argumentNames(fn); //['foo', 'bar']

bind

var fn = function(foo, bar) {
   return foo + bar;
};

argumentNames(fn); //-> ['foo', 'bar']

bindAsEventListener

var obj = { name: 'A nice demo' };

function handler(e) {
  var tag = Event.element(e).tagName.toLowerCase();
  var data = $A(arguments);
  data.shift();
  alert(this.name + '\nClick on a ' + tag + '\nOther args: ' + data.join(', '));
}

Event.observe(document, 'click', bindAsEventListener(obj, handler, 1, 2, 3));

curry

String.prototype.splitOnSpaces = curry(String.prototype.split, " ");
"foo bar baz thud".splitOnSpaces(); //-> ["foo", "bar", "baz", "thud"]

defer

function hideNewElement() {
  $('inserted').hide();
};

function insertThenHide(markup) {
  $('container').insert(markup);

  // Prototype XUL
  defer(hideNewElement);
}

insertThenHide("

Lorem ipsum

");

delay

// before:
window.setTimeout(function() {
Element.addClassName('foo', 'bar'); }, 1000);

// after:
delay(Element.addClassName, 1, 'foo', 'bar');

// clearing a timeout
var id = delay(Element.hide, 5, 'foo');
window.clearTimeout(id);

delay

// start off with a simple function that does an operation
// on the target object:
var fn = function(target, foo) {
  target.value = foo;
};

var object = {};

// use the original function
fn(object, 'bar');
object.value //-> 'bar'

// if we methodize it and copy over to the object, it becomes
// a method of the object and takes 1 argument less:

object.fnMethodized = methodize(fn);

object.fnMethodized('boom!');
object.value //-> 'boom!'

wrap

String.prototype.capitalize = wrap(String.prototype.capitalize,
  function(proceed, eachWord) {
    if (eachWord && this.include(" ")) {
      // capitalize each word in the string
      return this.split(" ").invoke("capitalize").join(" ");
    } else {
      // proceed using the original function
      return proceed();
    }
  });

"hello world".capitalize()     // "Hello world"
"hello world".capitalize(true) // "Hello World"