#!/usr/bin/perl -w
#Compute pi. Based on Leibniz's algorithm that
#       pi = 4 - 4/3 + 4/5 - 4/7 + 4/9 - 4/11...
use strict;

my $pi = 4;
my $next_digits = get_leibniz();

for ( 1 .. 100000 ) {
        my ( $subtract, $add ) =  &$next_digits;
        $pi = $pi - $subtract + $add;
}

print $pi;

sub get_leibniz {
        my $index = 1;
        my $sub = sub {
                $index += 2;
                my $first = 4/$index;
                $index += 2;
                my $second = 4/$index;
                return ($first, $second);
        };
        return $sub;
}

##</code><code>##

$p=4;$n=l();for(1..100000){($s,$a)=&$n;$p=$p-$s+$a}print$p;
sub l{$i=1;sub{$i+=2;$f=4/$i;$i+=2;$q=4/$i;($f,$q)}}