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.

Looping is simply a way for you to reduce the amount of code and/or content you have to write out. The idea is that you have something you have to do, or some content you have to show, and instead of just "writing it all out," you find a pattern to it - a common denominator - and let PHP execute the code or generate the content piece by piece using that pattern, based on a condition.

Their example solves the problem of finding taking a range of numbers and seeing how many of them can be evenly divided by another number.

I've released a new video tutorial covering PHP basics. In this video I teach three different loop types in PHP: For Loops, While Loops and Foreach Loops.

You can watch this video here or check out some of the other video tutorials he has posted on everything from conditionals to working with objects.