sub factorial {
    my ($num) = @_;
    @_ = (1, 1, $num);
    goto &_factorial;
}
                                                                                                         
sub _factorial {
    my ($result, $counter, $max) = @_;
    return $result if $counter > $max;
    @_ = (($result * $counter), ($counter + 1), $max);
    goto &_factorial;
}

##</code><code>##

my $_factorial;
$_factorial = sub {
    my ($result, $counter, $max) = @_;
    return $result if $counter > $max;
    @_ = (($result * $counter), ($counter + 1), $max);
    goto $_factorial;
};

sub factorial {
    my ($num) = @_;
    @_ = (1, 1, $num);
    goto $_factorial;
}

##</code><code>##

#!/usr/local/bin/perl
use warnings;
use strict;
use Benchmark;
use Test::More tests => 3;
 
my $_fact3;
$_fact3 = sub {
    my ($result, $counter, $max) = @_;
    return $result if $counter > $max;
    @_ = (($result * $counter), ($counter + 1), $max);
    goto $_fact3;
};
 
my $number = shift or die "No number supplied";
 
validate_factorial_routines($number);
 
print "Timing factorial of $number\n";
 
timethese(10000, {
    'recursion' => sub { fact1($number) },
    'typeglob'  => sub { fact2($number) },
    'lexical'   => sub { fact3($number) },
});
 
sub validate_factorial_routines {
    my $num = shift;
    my @result = (fact1($num), fact2($num), fact3($num));
    is(fact1(5), 120, 'fact1 should return the correct amount');
    is(fact2(5), 120, 'fact2 should return the correct amount');
    is(fact3(5), 120, 'fact3 should return the correct amount');
}
 
sub fact1 {
    my ($num) = @_;
    return _fact1(1,1,$num);
}
 
sub _fact1 {
    my ($result, $counter, $max) = @_;
    return $result if $counter > $max;
    return _fact1(($result * $counter), ($counter + 1), $max);
}
 
sub fact2 {
    my ($num) = @_;
    @_ = (1, 1, $num);
    goto &_fact2;
}
 
sub _fact2 {
    my ($result, $counter, $max) = @_;
    return $result if $counter > $max;
    @_ = (($result * $counter), ($counter + 1), $max);
    goto &_fact2;
}
 
sub fact3 {
    my ($num) = @_;
    @_ = (1, 1, $num);
    goto $_fact3;
}

__END__
1..3
ok 1 - fact1 should return the correct amount
ok 2 - fact2 should return the correct amount
ok 3 - fact3 should return the correct amount
Testing factorial of 30
120
Benchmark: timing 10000 iterations of lexical, recursion, typeglob...
   lexical:  4 wallclock secs ( 4.05 usr +  0.00 sys =  4.05 CPU) @ 2469.14/s (n=10000)
 recursion:  1 wallclock secs ( 1.45 usr +  0.00 sys =  1.45 CPU) @ 6896.55/s (n=10000)
  typeglob:  5 wallclock secs ( 4.28 usr +  0.00 sys =  4.28 CPU) @ 2336.45/s (n=10000)

##</code><code>##

1..3
ok 1 - fact1 should return the correct amount
ok 2 - fact2 should return the correct amount
ok 3 - fact3 should return the correct amount
Timing factorial of 30
Benchmark: timing 10000 iterations of lexical, recursion, typeglob...
   lexical:  4 wallclock secs ( 4.05 usr +  0.00 sys =  4.05 CPU) @ 2469.14/s (n=10000)
 recursion:  4 wallclock secs ( 3.87 usr +  0.00 sys =  3.87 CPU) @ 2583.98/s (n=10000)
  typeglob:  4 wallclock secs ( 4.28 usr +  0.00 sys =  4.28 CPU) @ 2336.45/s (n=10000)