this is a straight implementation of SignalSlot pattern in PHP

msgslot.php

<?php 
/*
 * @Script: Signal Slot
 * @Version: 0.1
 * @Author: Emad Elsaid
 * @Email: [email protected]
 * @Website: http://blazeeboy.blogspot.com
 * @What is that ?:
 * this is an implemntation of Signal/Slot pattern in PHP
 * you can bind group of functions to one or more signals
 * then you can send signals , it'll execute the group of 
 * functions in the same order you bind them.
 * 
 * function pp()
 * {
 * 	echo "print print";
 * }
 * 
 * SignalSlot::bind('print', 'pp' );
 * SignalSlot::send( 'print' );
 * 
 * 
 * Note: 	this class in is a Singleton, and it'll initialise itself 
 * 			on first use of any static method.
 */
 
// check if the class previously declared.
if( ! class_exists('SignalSlot') )
{
	class SignalSlot
	{
		// the singleton instance of that class
		static private $instance = NULL;
		// an associative array where slot as Key and functions as value array.
		private $signals = array();
		// constructor must be private in order to prevent making other instances
		private function __construct(){}
		
		// bind function to some signal.
		static public function bind( $signal, $function )
		{
			// signal and function must be strings
			if( !is_string($signal) or !is_string($function) )
			{
				throw new Exception( 'Signal and Function must be String' );
				return FALSE;
			}
			// function must exists
			if( !function_exists( $function ) )
			{
				throw new Exception( 'Function not exist' );
				return FALSE;
			}
			// initialise singleton if not initialised
			if( !is_object(SignalSlot::$instance) )
				SignalSlot::$instance = new SignalSlot();
			// initialise key with empty function if not exists
			if( !array_key_exists( $signal, SignalSlot::$instance->signals ) )
				SignalSlot::$instance->signals[$signal] = array();
			// add function to the signals array if not exists in the signal key.
			if( !in_array( $function, SignalSlot::$instance->signals[$signal] ) )
				SignalSlot::$instance->signals[$signal][] = $function;
				
			return TRUE;
		}
		
		// unlink function from signal
		static public function unbind( $signal, $function )
		{
			// signal and function must be strings
			if( !is_string($signal) or !is_string($function) )
			{
				throw new Exception( 'Signal and Function must be String' );
				return FALSE;
			}
			// initialise singleton if not initialised
			if( !is_object(SignalSlot::$instance) )
				SignalSlot::$instance = new SignalSlot();
			// if key exists and function position in the signals array not false
			// then unset it from that key's array
			if( array_key_exists( $signal, SignalSlot::$instance->signals ) 
				and array_search($function,SignalSlot::$instance->signals[$signal])!==FALSE )
			{
				unset(SignalSlot::$instance->signals[$signal]
					[array_search($function,SignalSlot::$instance->signals[$signal])]);
					
				return TRUE;
			}
			else
			{
				return FALSE;
			}
		}
		
		// send signal to execute all linked functions.
		static public function send( $signal )
		{
			// initialise singleton if not initialised
			if( !is_object(SignalSlot::$instance) )
				SignalSlot::$instance = new SignalSlot();
			// if that signal key not with us then return false
			if( !array_key_exists( $signal, SignalSlot::$instance->signals ) )
				return FALSE;
			// execute all functions to that key
			foreach( SignalSlot::$instance->signals[$signal] as $function )
				$function();
			
			return TRUE;
		}
		
	}
}