Learning an entirely new programming paradigm is surely an extremely refreshing experience. I've been having lots of Prolog fun today.

We've already established that I'm an established slacker. Out of the 17 or so AI lectures we've taken so far, I've only attended the first [lol]. I'm much better when it comes to classes, though, where we actually learn something, so I've attended like 4 out of 6.

Also, I usually only "study" for university 4 times a year: before the midterms and before the finals. Given that the AI mid-term is next Sunday, I had to see what all the fuss is about, so I started reading our course notes and exploring Prolog. And man, what an enjoyable paradigm and language. It's really enlightening to explore problem solving from an entirely different perspective - I encourage you to try it out if you hadn't already.

Given the following very simple rule, "You talk about someone either if you know him or you know someone who talks about him", the exercise asks you to create a prolog representation of it for the following And/Or tree:



So I quickly came up with this:


It recursed infinitely whenever I queried it with:
?- talks_about_r(X,Y).

Given how inexperienced I am, I couldn't figure out why except by running and tracing it. Can you?
Think about it...

...

Gave up?

Here's a sample run:


Even after taking a look at the above run, I couldn't find out what's going exactly. The derivation tree revealed what's going on:



You can see that the last derived node takes us to "talks_about(bill, Y)", which is going to be broken into 2 branches: "knows(bill, Y)" and "knows(bill, Y), talks_about_r(bill, Y)". Given that bill knows jane, the right branch takes us back to the point: "knows(bill, jane), talks_about_r(jane, Y)" and so on and on and on...[lol]

You can imagine that for a nublet like myself this thingy took quite some time to discover [grin]. I haven't really thought of a simple and elegant solution to prevent this yet, because I'm done for today - perhaps tomorrow. Until then, feel free to tell me your solution if you happen to know one.

So now I've added the 2nd thing to the list of things that bring me back to n00ber zone: Prolog (The first being leetox, of course).

Muhammad out.

dog(rocky).
cat(whatever).

person(jack).
person(jenny).

has_dog(jack, rocky).
has_cat(jenny, whatever).

has_pet(X, Y):- person(X), has_dog(X, Y).
has_pet(X, Y):- person(X), has_cat(X, Y).