February 22, 2014

Minimalist Asynchronous PVM

So adding support for asynchronous tasks turned out not to be so difficult. With a little help of Q's promises and support for composing them all it took was a minor rewrite of the main tick function...

Anyway, this version of the minimalist PVM can be found here, together with an example which queries the OpenWeatherMap API.

Note that in the process of doing this I also added some minor tweaks to the basic version of the PVM; the most useful of which is the ability to define a starting runtime state for the process upon activation. I extended the examples there as well to showcase this.

February 18, 2014

Minimalist Literate Programming

As a quick follow-up to the minimalist PVM you can now find a very simple literate programming tool over at my github. It's a single Perl script which converts source code into a Markdown document. It does this by extracting the text from the comments in the source code, and wrapping the code itself in code blocks. Want an example of the output ? The README.md for the tool is exactly that. (Self-documenting code FTW!)

February 15, 2014

Minimalist Process Virtual Machine

Over at my github account (see, I do have one) I just added a minimalist implementation of a Process Virtual Machine (PVM).

Wait, what ?

Let's start with what a PVM is. You can find a thorough description of it here, but in brief it is an engine which can drive automated business processes and workflows. It actually forms the core of JBPM and Activiti. (If you really feel like geeking out on workflow engines you should definitely head over to Joram Barrez's blog, which has all sorts of Activiti craziness in it.)

I really wanted to figure out what makes such an engine tick, and while I can look at the source code for JBPM and Activiti they were never meant as an educational example. These engines have real work to do, and so come with usual amount of hardening and boilerplating. Rather than deep-diving through all that I wanted to see what a minimalist implementation could look like.

When it comes to minimalist implementations a lot depends on your choice of language. Ideally you want something which is really flexible without imposing a lot of structure. Prototype-based languages are a great fit and, as it so happens, Javascript is a popular example of one.

So that's where I went. I've got a minimalist PVM capable of running in a Node.js environment. As you'll see there's very little code to it; and I actually spent most of the time getting everything into the form of a literate program.

Because it is very minimalist there are certain features it does not (yet) have. The big ones are wait states (e.g. for human interaction), asynchronous tasks (e.g. for doing IO or REST calls), and persistence. In a future version I'll see if I can add those in a minimalist way as well, but for now this will do to satisfy my curiousity.

If you like, let me know; and feel free to experiment further.