package ACME::WeightWatchers;
use Carp;
require Exporter;
our @ISA    = qw(Exporter);
our @EXPORT = 'watchsize';

sub watchsize {
  local $/ = "\n";
  my $caller = caller;
  open _, "$caller::$0";
  while (<_>) {
    $. == 40 
      and confess "no more Perl for me, unless less than 40 lines\n";
  }
}
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#!/usr/bin/perl
use strict;
use warnings;
use ACME::WeightWatchers;

watchsize();

# your code here ...
print "I made it under 40!\n";
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