#!/usr/bin/perl

use strict;
use warnings;
use Sub::Call::Recur qw(:all);
use Memoize;
memoize('sum');

sub sum { 
    my ( $n, $sum ) = @_;
    if ( $n == 0 ) {
        return $sum;
    }
    else {
        recur ( $n - 1, $sum + 1);
    }
}

foreach my $sum ( \&sum ) { 
  print $sum->(0, 0),    "\n",
        $sum->(0, 1),    "\n",
        $sum->(1, 0),    "\n", 
        $sum->(1, 1),    "\n",
        $sum->(2, 2),    "\n",
        $sum->(10, 1),   "\n",
        $sum->(1000, 1), "\n";
}