this is code in route

Route::post('form-submit', function(){
 //get all inputs
 $inputs = Input::all();
 //create array of validation rules
 $rules = array('username'=>'required|foo|min:4|max:35','email'=>'required|email');
 //set custom error messages
 $messages = array(
     'foo'=>'Field value must be foo'
 );
 //validate inputs
 $validator = Validator::make($inputs,$rules,$messages);
 if($validator->passes()){
  //inputs valid
  echo 'Well';
 }else{
  //return to form view with errors
  return Redirect::to('form')->withErrors($validator);
 }
});

but my main question is where the file is extended ... where will this code file where the function is declared "foo"

Validator::extend('foo', function($field,$value,$parameters){
 //return true if field value is foo
 return $value == 'foo';
});
Route::get('form', function(){
 //render app/views/form.blade.php
 return View::make('form');
});