To elaborate on LanX’s comments:

Before using Perl prototypes you should study Tom Christiansen’s essay, “Far More than Everything You’ve Ever Wanted to Know about Prototypes in Perl, ” which is available within the Monastery here. To quote from the opening:

Nearly any programmer you encounter will, when asked what function prototypes are for, report the standard text-book answer that function prototypes are mainly used to catch usage errors at compile time in functions called with an unexpected type or number of parameters. This is what programmers are expecting of prototypes, and what Perl does not give them.

Think coercion rather than checking, and you’ll be closer to the mark. Read the article, then use prototypes only for those specialised cases where they’re really useful.

Hope that helps,