gistfile1.aw

<?php


function example_menu() {
  $items[] = array();
  $items['some/pointless/url'] = array(
      'title' => t('Some Pointless Title'),
      'page callback' => 'pointless_navigator',
      'access arguments' => array('access content'),
      'type' => MENU_CALLBACK,
  );
  return $items;
}

function pointless_navigator() {
  global $user;

  if (user_access('view example') && user_access('view all example')) {
      drupal_goto("some/other/url/a");
  } else {
      drupal_goto("some/other/url/b");
  }
}