#!/usr/bin/perl

use warnings;
use strict;
use Getopt::Std;

our ($opt_t);
getopts('t');

if($opt_t){
   eval 'use Test::Simple tests => 3;';
   ok(double(2) == 4);
   ok(double(-3) == -6);
   ok(double(0) == 0);
   exit;
}

print join ' ',map(double($_),@ARGV),"\n";

sub double{
   my $a=shift;
   $a*2;
}