#! perl -slw
use strict;
use Benchmark qw[ cmpthese ];
no warnings 'recursion';

sub odd { my $number = shift; return !even ($number); }
sub even { my $number = abs shift; return 1 if $number == 0; return odd ($number - 1); }

cmpthese -5, {
    normal     => q[ my $n;     $_ & 1 and $n++ for 1 .. 1000; ],
    functional => q[ my $n; even( $_ ) and $n++ for 1 .. 1000; ],
};

__END__
c:\test>junk
              s/iter functional     normal
functional      1.50         --      -100%
normal     2.41e-004    625042%         --