From time to time, I find that I need to put a parser together. Most of the time I find that I need to do this in C for performance, but other times I just want something convenient, like PHP, and have been out of luck.

His result is two new packages - lemon-php and JLexPHP (under a BSDish license) you can download and compile on your own system.

Also, if you'll remember a while back, Greg Beaver had wanted something similar (as mentioned in the comments) and created his own lexer/generator as well.

Last week, I blogged about completing a port of the Lemon parser generator to PHP 5, which I thought was pretty cool. However, in an email, Alex Merz pointed out that without a lexer generator to accompany lemon, it's pretty difficult to write a decent parser.

After Alex's email, I started thinking about what it would take to write a lexer generator. Basically, a lexer generator requires parsing and compiling regular expressions, then scanning the source one character at a time to find matches. So, it occurred to me that perhaps simply combining regular expressions with sub-patterns could accomplish this task quite easily.

He goes on to explain this process, showing how a simple regular expresion call (and a look at its return arguments) could create a simple, easy solution. Since the re2c format is still unsupported in PHP (without a goto to go to), he opts to stick with the regular expressions and creates a "lex2php" format instead.

He's packaged up both halves of this setup and has already posted proposals for them to the PEAR site:

• PHP_LexerGenerator
• PHP_ParserGenerator

About three weeks ago, I looked at the state of the parser generator world out there for PHP, and it is pretty dismal. Antlr3 will theoretically support PHP 5 generation, but it's impossible to find any source in spite of several fruitless hours of googling.

I finally decided that if this is ever going to happen, I'll have to get off my butt and do it. So, two weeks ago, I grabbed the source of the Lemon parser generator from its website

He follows the path he took, using the code from the Lemon parser, translating it into a PHP version, and correcting a few bugs along the way.

In the process, I have a fully working PGN file parser that will make its way into a PEAR proposal as soon as I get around to integrating it with Games_Chess to do full validation of the contents of the PGN file. However, the parser works 100% even with some of the weirdest PGN things I could throw at it.

He finishes off the post with some example code, including a method for using it on the command line. You can grab the code for the project and related files here

Sebastian Bergmann also comments in his blog about the work Greg's done.