/user_delete.php

<?php
require_once('boot.php');

if(!empty($_POST['user_id'])){
  $delete_user = new User($_POST['user_id']);
  $delete_user->set(array('id'=>$_POST['user_id']));
  trigger_error($delete_user->id);
  if($delete_user->deleteData($_POST['user_id'])){
    header("Location: user_list.php");
    exit();
  }
}

bail('failed to delete user');