If you don't want to run the program again with diagnostics turned on, you can give splain the error message

$ perl -we" f(3); sub f($){die} "
main::f() called too early to check prototype at -e line 1.
Died at -e line 1.

$ echo main::f() called too early to check prototype at -e line 1. |sp
+lain
main::f() called too early to check prototype at -e line 1.  (#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 a
+n
    early prototype declaration for the subroutine in question, or mov
+e the
    subroutine definition ahead of the call to get proper prototype
    checking.  Alternatively, if you are certain that you're calling t
+he
    function correctly, you may put an ampersand before the name to av
+oid
    the warning.  See perlsub.
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