Since I left these out of the code I posted, and since some people did not follow the Help Name This Module thread, here is some documentation for the Loop::Watch module.

Abstract

Loop::Watch is like alarm() for variables -- it watches a given set of variables (scalars, arrays, and hashes are the only ones currently supported), and exits a block of code (which may or may not be a loop) as soon as the condition it is given becomes false. It's like a while-loop that keeps tabs on the condition constantly.

Usage

Let's say you wanted to do a series of statements, but stop as soon as one of them caused $temperature to go below 0, and if none caused that, to continue normally with the rest of the program.

use Loop::Watch;

my $temp = 20;  # celsius, that is

# doing { ... } does *not* loop
ensure { $temp >= 0 } watching($temp), doing {
  move_to_florida();
  wait_until_winter();
  move_to_new_jersey();
  wait_until_spring();
  move_to_montana();
  wait_until_fall();
  move_to_alaska();
  wait_until_winter();
};
[download]

That code would probably stop somewhere around the move to New Jersey. That function could do any number of things to $temperature, and this module keeps an eye on things.

Let's say, though, you wanted to circle the globe until your money ran out:

use Loop::Watch;

my $money = 1_000_000;  # in USD

# looping { ... } *does* loop
ensure { $money > 0 } watching($money), looping {
  circle_globe();
};

sub circle_globe {
  move_to_next_location();
  purchase_lodging();
  eat();
  # ...
}
[download]

This allows the functions called by circle_globe() to assume you have money left -- and as soon as you don't have any money left, you stop your trip.

You can watch multiple variables in the same block:

use Loop::Watch;

my ($age, @companies);
$age = 20;

ensure { $age < 35 and @companies < 10 }
watching($age, \@companies),
looping {
  $age++ if new_year();
  if (my $c = acquisition_available()) {
    if (try_to_purchase($c)) {
      push @companies, $c;
      check_related($c);
    }
  }
};
[download]

That code will stop once you've reached 35 (good age to retire at) or you've acquired 10 companies. Maybe during the course of the new_year(), you lose a company or something -- that's ok. You needn't do any checking there, all the checking of the age and company count is done by the module.

japhy -- Perl and Regex Hacker