PHPTuring

A few years ago, as an exercise in Test-Driven Development, I wrote a Turing machine simulator in PHP and imaginatively named it PHPTuring.

I had completely forgotten about it until today, when I dug it out for another look. Truth be told, I still haven't seen a Turing machine done any better in PHP, and apart from a few syntactical niceties (removing closing PHP tags as per the Zend way, neatening up the PHPDoc blocks) I'm actually pretty comfortable with the code.

Using it is a breeze. It reads pipe-separated tapes and newline plus pipe-separated instruction sets like so:

<?php

$prog = '0|1|1|R|0\n0||1|R|1\n1|1|1|R|1\n1|||L|2\n2|1|||stop';
$tape = '1|1|1|1|1|1||1|1|1|1|1|1|1|1';

$machine  = new Machine();
$compiler = new SimpleCompiler();
$parser   = new SimpleTapeParser();
$debugger = new SimpleDebugger();

$debugger->watch($machine);

header('Content-type: text/plain');
$machine->run($compiler->compile($prog),
              $parser->parse($tape));

It should work with other formats, so long as someone writes parsers for them. Similarly, the debugger is just an Observer that dumps the state and tape to the screen at each step, but it could easily do something more subtle some day.

The code ships with full tests, and is available for download on PHPTuring's Sourceforge download page.

So why am I banging on about it here? I don't know. Maybe just because I like it, because it was the first afternoon's coding that really got me test-infected, and because I'd be interested in any feedback.

The Get Up Kids are The Greatest Band That Ever Existed

The Get Up Kids are the greatest band that ever existed. To prove this, I would like to draw your attention to some very early live footage.

MySQL versus PostgreSQL: Adding a 'Last Modified Time' Column to a Table

This is the second post here detailing my ongoing adventures with PostgreSQL. This time I had a requirement to add a "timestamp" column to a table. The point of this being to allow us to track the "last modified" time of a row, without requiring that the application code manage the timestamp itself.

There's a lot of reasons why you might wish to do this. In this case it was to simplify syncing the data into a data warehouse. More specifically, to allow the DBA to easily identify rows which have changed since the last import.

Having done this a couple of times in MySQL, I assumed that the process would be straightforward. I should know better by now!

An Introduction to Tera-WURFL

I recently added a post about Wurfl, a comprehensive open-source XML database of mobile device capabilities. I noted that actually querying Wurfl in a performant manner:

is going to be a non-trivial task, and is perhaps a topic for a further article.

Well, I guess this is that article. It's time to have a look at Tera-WURFL, which is perhaps the most popular tool for querying Wurfl programmatically - from PHP, at least.

Herding Cats

For as long as anyone can remember, the term "herding cats" has been used as an analogy for the challenges involved in managing developers. The implication being, of course, that developers tend to be smart, wilful, single-minded folks. Personal experience suggests this is often the case.

The analogy was reflected in the title of a book named "Herding Cats: A Primer for Programmers who Lead Programmers", written by the impressively named J. Hank Rainwater. I mention it because this is a decent read for anyone who develops, or who works with developers - whether in a management capacity or not. It's not in the same league as "The Pragmatic Programmer", but I'm getting off the point now.

So anyway, I came across this video via Yahoo MySQL guru Jeremy Zawodny's blog. It's so slickly made that you're not surprised when it turns out to be an ad for a big expensive professional services company. But I liked it.

MySQL versus PostgreSQL: Adding an Auto-Increment Column to a Table

The bulk of my database experience (almost eight years now) has been with the popular open-source MySQL database management system. MySQL has progressed significantly over the years, and has grown into a remarkable product. It finally has all the must-have features such as views, stored procs and referential integrity, coupled with the blistering performance for which MySQL has always been known. In short, it rocks.

But I digress. I've recently been having to get to grips with PostgreSQL (an old version of course - 7.1 or so - just to make life really interesting). It's largely intuitive, but there are quirks around most corners. This is my favourite so far: I recently needed to add an auto-incrementing integer "id" column to a table.