#!/usr/bin/perl

use strict;

my $sub = do {
    my $this_sub;

    $this_sub = sub {
	my $factor = int(shift);
	return $factor > 1
	    ? &$this_sub($factor-1) * $factor
	    : 1;
    };

};

print "factorial of 7 is ".&$sub(7)."\n";