Change MainLoop; to MainLoop(); to fix the problem. MainLoop; is only the same as MainLoop(); if, at the time that it is compiled, you have already declared a subroutine with that name. Otherwise it is a bareword which is either the same as "MainLoop"; (if strict isn't on) or is a fatal error.

Read (tye)Re: use vs. require and Conditional compile-time magic (RE: Checking to see if a particular Module is installed) for more to meditate on.

Thanks to ybiC for pointing this out.