Matthew Turland set out a while back to develop a bot in PHP. The result of it is Phergie an "an IRC bot written in PHP 5 with an OO API" that can be extended with components for a wide variety of features. Another pleasant offshoot from his project is this first part of two articles on the C7Y community site detailing its creation.
The PHP Community channel on the Freenode IRC network, #phpc, had a longstanding bot called "Ai". Like many bots at the time of her creation, she was based on PHP 4. [...] With the coming end-of-life of PHP 4 and at the encouragement of channel users, I decided to start a project to develop a new bot based on PHP 5 that would fully utilize its new object model and offer users a chance to contribute to the bot they used in their channel.
Matthew talks about the initial stages of development (planning, research) and some of the development process of the bootstrap file, configuration file, and driver as well as the event handling.