$ echo foo() called too early to check prototype at file line 12 |splain
foo() called too early to check prototype at file line 12  (#1)
    (W prototype) You've called a function that has a prototype before the
    parser saw a definition or declaration for it, and Perl could not check
    that the call conforms to the prototype.  You need to either add an
    early prototype declaration for the subroutine in question, or move the
    subroutine definition ahead of the call to get proper prototype
    checking.  Alternatively, if you are certain that you're calling the
    function correctly, you may put an ampersand before the name to avoid
    the warning.  See perlsub.