jeff.dallien.net

When I’m at a B’more on Rails meeting, I might do more listening than talking but just attending gets me excited to work on things, especially when I hear what others are working on. So when I got home from tonight’s meeting I thought I would spend some time on one of the programming tasks on my todo list.

A couple of months ago while waiting for the January B’more on Rails meeting to start, I noticed that prologblog.com was available and I thought it would be not only a good learning experience but also beneficial to the Prolog community to have a site dedicated to practical Prolog programming. I could have had the site running long ago, except that my big idea was that I wanted to write the blog app itself in Prolog. The most Prolog code people are usually exposed to is some simple example of unification, like:

man(bob).
man(fred).
parent(fred, bob).

father(X,Y) :- parent(X,Y), man(X), man(Y).
son(X,Y) :- father(Y,X).

and so starting off with an actual application that isn’t too complicated but is at least useful, like a blog, seemed like a good idea.

I originally looked for an existing framework for Prolog web applications. The only thing I found was something called Prosper, which looked promising but has a dependency on a Windows-specific C library. I decided not to spend the time to port this code since I had no clue whether the Prosper framework was even going to be useful for me.

My next thought was to write some simple Prolog application myself, and connect it to the web server via Rack and Passenger. The hurdle to doing that was finding a Ruby interface to SWI-Prolog, in which I planned to write the application. When I couldn’t find an interface, the work to write that code became a bigger job than writing the Prolog code itself.

The paths to my goal which I thought to be the shortest were growing longer in front of me and were filled with a lot of boring work before I could get to the part that interested me. So, today I decided to tackle the problem with the mindset of using “the simplest thing which could possibly work.” The first thing that came to mind was to use perl, which I knew had some existing modules for connecting to SWI-Prolog and would of course would very easily handle requests from Apache and passing them on to Prolog.

I tried installing two different SWI perl modules and neither one would build the C code they needed properly. After installing some missing libraries I eventually ran into more compilation errors. I was now faced with my “simplest thing” being another long boring road to reach even a small amount of satisfaction.

The final result is that prologblog.com is no more live than it was when I wasn’t working on it. I’ve seen some threads on “using Prolog from PHP” where by “using” they really just mean a system call to the Prolog interpreter and inserting the output into the PHP page. I could use the same approach with any language ruby, perl, etc. but it feels clunky and it is definitely ugly. However, it is now my most likely “simplest thing that could possibly work,” which I may use just to get the project off the ground while I figure out something better.