laravel/laravel — pull request #525 by franzliedke (2012-04-11 11:58:26+00:00)
Title: Use is_callable() for checking lambdas

In the value() function, up till now you were checking with

$value instanceof Closure

whether the given variable (`$value`) was a valid closure. However, as stated in the [PHP Manual](http://php.net/manual/en/functions.anonymous.php), this is an "implemention detail" and should not be relied upon.

Thus, it is better to use `is_callable()`.