jeff.dallien.net

Clearly the future of digital advertising is to waste money on meaningless context-sensitive ads that go nowhere.

Just in case this was some clever advertising for some amazing new site on testing, I clicked the ad. It took me to this:

The site is now up again but unfortunately they don’t deal in the kind of testing I care about.

Really carryoutmenu.com? Three giant red errors? For something that any user might do while normally using your site?

In the last couple of weeks I have been able to come back to doing some Prolog development at work after a very long break from it. I didn’t realize it before but my feelings toward writing Prolog code had been somewhat negatively affected by our troubles deploying Rails apps that call a particular Prolog interpreter. I had forgotten that I actually do really enjoy writing Prolog code. Here’s some quick thoughts on why I enjoy it and on a new project I’m starting where I hope to elaborate on these points.

Can be very fast

The code I have been maintaining lately is a scheduler. Although the data goes through a lot of processing before it reaches the Prolog code, the scheduler itself runs very fast. It can return a schedule for a consistent constraint network of hundreds of nodes in under a second.

Easy to gather data

A number of times the Rails side of our application required new information from the Prolog side. We have a clear, agreed upon API to call and return results between the two, and it was very easy to write new code to calculate and gather the extra information and make it part of our API for returning data.

Easily handles different cases

The system of backtracking used in Prolog lets the programmer describe any number of situations and what to do in each of them and the Prolog interpreter does the work of finding which apply to the current data.

Reliable

Of course it is possible to write buggy code in any language, but part of the good vibes I have for Prolog stem from the reliability of this particular work project. After the initial development the code was, and continues to be, very reliable (ignoring our deployment issues which weren’t related to the code itself). While the Ruby code calling Prolog changed and added features, only minor tweaks in the Prolog code were required for well over a year.

A modern Prolog site

From searches and blog monitoring, it is clear that Prolog gets little to no love, even in this time of open mindedness and people learning new and varied languages. I think part of that comes from the fact that Prolog’s main usage has not been in areas that a lot of people are interested in. I’ve written schedulers and theorem provers in Prolog, but not many small, useful apps or just something thrown together for fun.

To hopefully start discussions on this type of Prolog programming, and to highlight more accessible Prolog coding, I have started working on http://prologblog.com. The first posts I plan to make there will be about writing the site’s own blog application in Prolog itself.

I have started looking into Erlang recently. I have been intrigued enough that I am going to make learning Erlang and producing something useful with it my first personal programming goal of 2009.

To help me do so I am starting with the Programming Erlang book from Pragmatic Bookshelf and also the first three parts in their Erlang in Practice set of screencasts.

I find Erlang interesting because of some very obvious similarities to Prolog. This is not really surprising since Prolog is a part of Erlang’s history; the first implementation of Erlang was in Prolog. The fact that I use Prolog regularly has let me skim through some of the things that the Erlang tutorials and books seem to spend time saying “now I know this isn’t like other languages you use” but for a Prolog programmer, many of these things aren’t surprising anymore.

Another intriguing thing about Erlang is that which differentiates it from Prolog. For me that is the focus on networking and multiple processes. These are things which, while doable, were not common things to do in Prolog programming.

Since it is early going in this process I have more questions than answers at this point. I am curious what parts of Prolog I am not going to have in Erlang which I am going to really miss or maybe even having a hard time functioning without.

While I am sure the Erlang community is still small, as is the Prolog community, at least it will be more active right now (I hope!). I have a Google blog search on “prolog” and to call the rate of new posts a ‘trickle’ would be optimistic.

As I work on my goal I’ll write more about my Erlang experiences and how a Prolog programming perspective helps or hinders the learning process.