Short version: Don't use prototypes.

Less short version: No, Really, Don't use prototypes.

Long version: Prototypes (almost always) don't do what you want or what you think. Most people who use prototypes frequently come from a C or C++ background and they have carried over their function declaration habits to Perl without noticing that there are almost none of the type checking benefits and several subtle traps. So, don't do that.