#!/usr/bin/perl
use strict;

sub foo {
    print defined $_[0] ? "It is me, $_[1]!\n" :
                          "$_[1] does no live here.\n";
}

my $sub = *nonfoo{CODE};
foo($sub, "nonfoo");

$sub = *foo{CODE};
foo($sub, "foo");
__END__
nonfoo does no live here.
It is me, foo!