Jani Hartikainen has posted the second article in his series looking at parsing PHP with Haskell (part one is here). In this new article he builds on the parser he built last time and gets to the actual evaluation of the PHP code.

Last week I wrote a post about a PHP parser / evaluator I wrote in Haskell. I explained some of the parts on how the parser itself was designed to process PHP code into an abstract source tree. Continuing from where we left off in the previous part, in this post I’ll discuss the actual evaluation part.

He starts by introducing the structure of the evaluator script, how it's broken up into functionality based on the type of object/data type being handled. He uses a "custom monad transformer stack" to handle the environment for the evaluation as is progresses. He talks about handling statements and expressions, declaring custom functions and the actual execution of the function call. There's also a mention of handling conditionals/looping as well as dealing with PHP's type juggling.

if you're interested in seeing the final result (and maybe trying it out for yourself) you can find the full source on Github.