++ed by:

1 PAUSE user(s)

Breno G. de Oliveira


Sub::Frequency - Run code blocks according to a given probability


    use Sub::Frequency;

    always {
        # code here will always run

    usually {
        # code here will run 75% of the time
        # 'normally' also works

    sometimes {
        # code here will run 50% of the time
        # 'maybe' also works

    rarely {
        # code here will run 25% of the time
        # 'seldom' also works

    never {
        # code here will never run

You can also specify your own probability for the code to run:

    with_probability 0.42 => sub {


This module provides a small DSL to deal with an event's frequency, or likelyness of happening.

Potential aplications include games, pseudo-random events and anything that may or may not run with a given probability.


All functions are exported by default using Exporter.

If you need to rename any of the keywords, consider using Sub::Import to get Sub::Exporter's flexibility.

always (&)

Takes a mandatory subroutine and executes it every time.

usually (&)

normally (&)

Takes a mandatory subroutine and executes it with a probability of 75%.

sometimes (&)

maybe (&)

Takes a mandatory subroutine and executes it with a probability of 50%.

rarely (&)

seldom (&)

Takes a mandatory subroutine and executes it with a probability of 25%.

never (&)

Takes a mandatory subroutine and does nothing.

with_probability ($;&)

Takes a probability and a subroutine, and executes the subroutine with the given probability.

The probability may be a real number between 0 and 1, or a percentage, passed as a string:

    with_probability 0.79 => \&foo;

    with_probability '79%' => \&bar;

Also, for greater flexibility, spaces around the number are trimmed, and we don't care about leading zeros:

    with_probability .04 => \&baz;

    with_probability ' .4  %  ' => \&something;

And you can, of course, replace the => with a ,:

    with_probability 20, {
        say "Mutley, do something!"


"'$foo' does not look like a number or a percentage."

Hint: Are you using something other than '.' as your floating point separator?

This coercion error may occur when you try passing a scalar to with_probability() with something that doesn't look like a number or a percentage. Like:

    with_probability 'monkey', { say 'some code' };

In the code above, you should replace 'monkey' with a number between 0 and 1, or a percentage string (such as '15%').


Breno G. de Oliveira, <garu at cpan.org>

Tiago Peczenyj


Please report any bugs or feature requests to bug-sub-frequency at rt.cpan.org, or through the web interface at http://rt.cpan.org/NoAuth/ReportBug.html?Queue=Sub-Frequency. I will be notified, and then you'll automatically be notified of progress on your bug as I make changes.


You can find documentation for this module with the perldoc command.

    perldoc Sub::Frequency

You can also look for information at:


Copyright 2010 Breno G. de Oliveira, Tiago Peczenyj.

This program is free software; you can redistribute it and/or modify it under the terms of either: the GNU General Public License as published by the Free Software Foundation; or the Artistic License.

See http://dev.perl.org/licenses/ for more information.