use strict;
use warnings;

foo('bar');

BEGIN{
    sub foo ($){
        print "foo called: @_\n";
    }
}
# gives warning message:
# main::foo() called too early to check prototype ...

##</code><code>##

use strict;
use warnings;

sub foo ($);

foo('bar');

sub foo ($){
    print "foo called: @_\n";
}