<?php

function invoke($hook, &$args, $op = 'run', $phase = '' ) {
  static $hooks = array();

  switch($op) {
    case 'run':
      //$call: $args->$result
      //php shape: function call( &$args, &$result ) //APS - accumulator passing style
      foreach( array('before', 'at' ,'after') as $phase ) {
        while(current( $hooks[$hook][$phase] )) {
          $cb = key(  $hooks[$hook][$phase] );
          $cb($args, $result ); 
          //swap the two
          next( $hooks[$hook][$phase] );
        }
      }
      return $result;
      
    case 'add':
      $hooks[$hook][$phase][$args] = true;
      break;
    case 'remove':
      unset( $hooks[$hook][$phase][$args]);
      break;
  }
}

//adding sugar
function hook_before( $hook, $cb ) {
  invoke( $hook, $cb, 'add', 'before');
}

function hook_at( $hook, $cb ) {
  invoke( $hook, $cb, 'add', 'at');
}

function hook_after( $hook, $cb ) {
  invoke( $hook, $cb, 'add', 'after');
}

function unhook_before( $hook, $cb ) {
  invoke( $hook, $cb, 'remove', 'before');
}

function unhook_at( $hook, $cb ) {
  invoke( $hook, $cb, 'remove', 'at');
}

function unhook_after( $hook, $cb ) {
  invoke( $hook, $cb, 'remove', 'after');
}

//example
function th1(&$args,&$result) {
  $result['func'][]='th1';
  print "in th1\n";
}

function th2(&$args,&$result) {
  $result['func'][]='th1';
  print "in th2\n";
}

function bth(&$args, &$result ) {
  $result['func'][]='bth';
  print "in bth\n";
}

function ath(&$args, &$result) {
  $result['func'][]='tah1';
  print "in ath\n";
}

//build program
hook_at('example','th1');
hook_at('example','th2');
hook_before('example','bth');
hook_after('example','ath');

//execute
print "\nreturned: " . var_export( invoke('example', $something ), true);

?>