About six months after the release of Tawny-OWL 1.1.0 (n.d.a) I am pleased to announce the 1.2 release. There have been a number of changes in this release, some planned, some not.

In this post, I describe the different technologies that I’ve tried for writing a new book, from markdown to LaTeX.

Yesterday, I came across a very strange bug in my Tawny-OWL library (n.d.a) The bug was my fault, but fixing it was exacerbated by what has to go into my list of Clojure gotchas (n.d.b)

Godwin’s law says that sooner or later every argument on the internet ends up with someone being called a Nazi. Interestingly in the Open Access debate, this has turned out not to be true; in this case, it’s been communists instead.

I first discovered the Visitors pattern from reading the original design patterns book, sometime in the last century when, having jumped into computer science, I was busy hoovering up everything I could about programming. After reading the chapter on visitors, it made no sense to me then and I had no real cause to go near them again until I started working on Tawny-OWL (n.d.a) This library includes a renderer which takes a set of OWL API OWLObjects and turns them into Clojure data structures. Originally, I added this simply to generate documentation, but since then it’s grown to have rather a life of its own. In Java, this would be be implemented with a visitor. In Clojure, I implemented this with multimethods which is often used as a replacement for the visitor pattern but I am now far from convinced that this was a good decision, after the performance of my code collapsed massively. In this article, I describe the problems with multimethods, and some alternatives. For each of these, I use a small example, and bench mark them; you can follow my code on https://github.com/phillord/visitor-benchmark. The results are, perhaps, a little surprising. This should be of relevance to anyone addressing the same problem in Clojure.