Operator precedence parsers are very simple on the surface. So don't feel in the least bit intimidated, because by the time you've read through this I hope to have you walk away with a solid foundation on how to write your very own operator precedence parser. The goal is to understand how to solve the problem of operator precedence parsing, and not necessarily to write your own parser. Learning how the problem can be solved is the most important thing to take away from this article.

He starts with an introduction to the concepts behind "operator precedence" including processing order and grouping. He also mentions infix and postfix (RPN) notations for handling different formats of equations. He used the "Shunting-yard Algorithm" and how it relates to handling the different parts of the equation, one at a time, in the correct order. He rest of the post is dedicated to the details of the execution in the tool, including code examples and the tokenization of the strings passed into it.

During this talk an introduction will be given to parsing. Terms like 'formal grammar', 'lexing / scanning', 'LL / LALR / PEG' will be explained and put into context. We will look at a recursive descent parsing as a practical way to parse languages. Finally the audience will be left with ways to get started with parsing structured text into memory.

You can listen to this latest episode either through the in-page player or by downloading the mp3. You can also see the slides from the presentation on Slideshare.

After looking around for a while [for a good resource on compilers] I settled for Terence Parr's Language Implementation Patterns. This is exactly what I needed - bit sized patterns on compiler and parser design with working code. The book provides a recipe style approach, gradually moving from simple to complex compiler/parser design issues. As I primarily work with PHP, I thought of porting some code to PHP to see how it works.

He shows examples using his custom tool to show a basic lexer output for a list and a complete listing of the code involved. Ultimately, though, he finds that PHP isn't overly suited to the task - anything more than his simple example could be more trouble than it's worth.

Parser tables, along with a lexer table, are the core constituents of any compiler's front end. This LALR parser generator is heavily based on my custom Php version of the map/reduce programming technique (functional programming). I will elaborate in future posts, on why I used a map/reduce basis to implement the parser generator.

Parsers organize a set of tokens based on the rules of a formal language the parser is given. Several of the grammar text files are included in the download so you can test it out for yourself. For more on the topic check out these two posts.

His examples include:

• String vs. numeric handling
• That PHP supports octal numbers "by accident"
• A lexer bug with hex values
• A parser bug involving the ternary operator

Comments on the post include those supporting the "die" opinion - that PHP just doesn't have it together like other languages - and those taking a bit more balanced approach on PHP's strengths and weaknesses.

Not wanting to spend too much time re-inventing the wheel I had a look at existing templating engines and decided to use Dwoo. [...] So after a little head-scratching, we now have CodeIgniter-Dwoo. DwooParser? DwooIgniter? Whatever we call it, my new Dwoo implementation for CodeIgniter sits in with "the CodeIgniter way" perfectly and the only code you will need to change within your application is the Parser file and your view files. No changes to your controllers at all!

You can download the library from the code section of his site.

• the Simple HTML DOM Parser
• Zend_Dom_Query
• phpQuery

Check out a previous tutorial of his for more information on using DOM parsers to scrape information from remote sites.

Who doesn't dream about it: Your own programming language, because the syntax and the word are expression! A step continue to go to ascend and from the programming language user to the language creator! This is now possible in PHP, but unfortunately only with minimum documentation.

He provides an example of the Lexer/Generator in action - handling a simple mathematical operation. The execution code is first with the Lexer definition file and the code for the parser following. Lastly, he has included the code to make things work - passing the test string into his custom Lexer which is passed off to the Parser and a value returned.

Yesterday I was struggling trying to get svn log to display the results for a certain user and this was very annoying.. then I jumped on #svn on freenode, and someone mentionned svn log --xml

This apparently made my life much much easier with this simple script I have pulled in a couple minutes.

He includes the script and a brief set of instructions on how to use it in your installation.

Since I'm used to the format from Ruby and Perl and since it's used for a similar purpose in the PHP Symfony framework, I also suggested using YAML configuration files since they are far more readable than XML and remain machine readable. I believe this went over quite well. Later on I realised the Zend Framework has no YAML support, and after some searching noticed the only (apparent) PHP parser was the Spyc library

So I fired off a few emails to the fw-general mailing list of the Zend Framework to see if there was any interest. I'd like to thank Matthew and Gavin for their feedback and I've since decided to have a go at implementing a YAML parser in PHP.

He notes that there is already a YAML parser for PHP5 (Syck), but that creating one for the Zend Framework is a different animal. He finishes up the post talking about where to start with the parser, what it is, and the next steps for him in its development.