Is it possible for a module to define patterns?

This should already be possible by creating a folder called "patterns" inside your module folder and then adding your patterns there. It was added in the last month with the following commit/revision:

http://drupal.org/cvs?commit=242188
http://cvs.drupal.org/viewvc.py/drupal/contributions/modules/patterns/pa...

Please try that and confirm it's working as intended for you.

Cheers!

I forgot to mention that a module can supply a pattern to be run when that module is installed: From the patterns.module file...

/**
 * Execute default configuration for module during the module installation
 *
 * This function should be called by other modules from
 * within their hook_enable() implementation.
 * Module should also provide modulename.config file containing PHP array
 * with the actions that need to be executed.
 *
 * @param $module
 *   name of the module calling the function
 */

You can do this now, but recent changes make it require an extra step then what Chris posted above.

Basically you need to have your module implement hook_patterns_directory() and return the path to a directory that can contain either a /patterns directory, or a /components directory for use with the patterns module. So in you're module if you were to implement that hook and do: return drupal_get_path('module', 'mymodule'); it would look in /path/to/your/module/patterns for available patterns.