The SitePoint PHP blog has a new tutorial posted (a repost from this article used with permission) about implementing a new operator in the PHP core language: a "range" operator. This operator allows the definition of a range of values (integer/float) as an internal PHP representation.

In the post below, Thomas Punt implements the range operator in PHP. If you’ve ever been interested in PHP internals and adding features to your favorite programming language, now’s the time to learn! This article will demonstrate how to implement a new operator in PHP. The following steps will be taken to do this: updating the lexer, updating the parser, updating the compilation stage and updating the Zend VM. This article therefore seeks to provide a brief overview of a number of PHP’s internal aspects.

He starts with a look at the range operator and how the intended functionality would work (including when the errors would be thrown). He then goes through the steps listed above and makes additions to the source, complete with the C code to make each change. The article is not only a good look at how to add a custom operator but also gives a good overview of the internals of PHP and how things fit together.