A callback function is a function you pass to another function, such as visitor in the following example: 

$tree->visit(\&visitor);

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Since you can't get a reference to system, you can't pass a reference to system, so you couldn't use it as a callback even if it made sense to do so.

In reply to Re: quick amateurish question by ikegami
in thread quick amateurish question by PerlZealot

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