The other day I uploaded a new experimental project on GitHub - A Haskell PHP parser / evaluator. It doesn't understand 100% of all PHP syntax, but it was an interesting experiment nevertheless. Here's some insights and other thoughts from working on the code.
He gets the "why?" question out of the way early, noting that it was mainly a desire to play with Haskell and figured parsing something he already knew well was a good first project. He also mentions the "Parsec" library that seems well suited for the parsing part of the process. There were some issues that he came across, however including dealing with PHP's weak typing and handling all of the possible incarnations of PHP script structure. He includes an example AST showing his different data structures (PHPValue, PHPExpr and PHPStmt). The next part of the series will be more about the evaluation of this structure.