[jrockway]

Read PHP's parser.

[sorbits]

The parser in PHP 3 and up was written by Zeev Suraski and Andi Gutmans: http://en.wikipedia.org/wiki/PHP

[sjf]

The original parser was written by Lerdorf (source: your wikipedia link).

But I don't think any of them have anything to be proud of: http://www.steike.com/code/php-must-die/

[jawngee]

swoosh