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Ovid (2709)

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Stuff with the Perl Foundation. A couple of patches in the Perl core. A few CPAN modules. That about sums it up.

Journal of Ovid (2709)

Monday May 16, 2005
01:31 AM

Hobbled. Solving Prolog Puzzles.

[ #24715 ]

Being laid up with a bad foot, I decided to work through more of the Amzi! Prolog tutorial. I really like the tutorial as it's clearly written and show how things operate under the hood. I read the lists chapter to see if I could learn techniques to better explain lists. Unfortunately, they are something that you'll either get or your won't. However, working through each of the exercises is like solving a bunch of mini-logic puzzles. I like that.

Here's my stab at various questions (they can be harder than they look, but as is often the case, a simpler answer is more likely to be correct).

  • Remove a given element from a list

    remove(X,[Head|Tail],[Head|Remainder]) :-

  • Find the element after a given element

    next(X,[_|Tail],Y) :-

  • Split a list into two lists at a given element (this is really simple, but I made it very complicated at first)

    split(X,List, Before, After) :-
        append(Before, [X|After],List).

  • Get the last element of a list (isn

    last([_|Tail],X) :- last(Tail,X).

  • Count the elements in a list

    length([_|TAIL],N) :-
        N is N1 + 1.

That last one was tricky because the math must be done last to ensure the N1 variable is instantiated since math is not done logically in Prolog.

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