>>156
use is required because not having it would change PHP's semantics in lambda-expressions from what they are in traditional functions, and more importantly, because PHP has features that would make it impossible to determine which variables from outer environments are accessed, and they didn't want to save the whole environments. For example, how would you detect you're accessing outer $hello if you did...:
$x = 'he' . 'llo';
$$x += 1;