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The Power of Prolog

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Re: The Power of Prolog

#161

Post by carapace »

zmonx wrote: post #153
carapace wrote: post #151

Earlier quoted context omitted.

I worked up this from the SEND MORE MONEY example in the CLP(FD) repo. https://gist.github.com/calroc/603ed919bc814ccee10c1b3df6142... There are five houses. The Englishman lives in the red house. The Spaniard owns the dog. Coffee is drunk in the green house. The Ukrainian drinks tea. The green house is immediately to the right of the ivory house. The Old Gold smoker owns snails. Kools are smoked in the yellow house.…

That's one of the most elegant Prolog formulations of this task I have seen so far. Great use of CLP(FD), especially considering that you have only started to learn this technology, as you mentioned in the other thread! I have only two small suggestion: First, since you know that Vars = [GreenHouse, ...] (the Prolog program states this as a constraint), you can simply substitute Vars every time for this list. Therefo…

That's very kind of you. Your comment made my day! :-)

I came to Logic Programming via grokking mrocklin's port of Kanren to Python: https://github.com/logpy/logpy; and to solving logic puzzles via Laws of Form: http://www.markability.net/ (Last year the author of that site George Burnett-Stuart apparently cracked how to encode Predicate Calculus in the notation, which is an exciting development, IMHO!) So I'm not a complete novice. That said, at first I thought I should define relations like smokes and pet_of, but somehow between seeing the table on the Wikipedia entry for the Zebra Puzzle and the SEND MORE MONEY example (https://github.com/triska/clpfd/blob/master/sendmory.pl) it became obvious what to do. If you look at the SEND MORE MONEY solution you'll see the Zebra solution is laid out just like it. To me, it seems like the same sort of puzzle as Sudoku, but much simpler. It's unfortunate that the solution and the solving proper (querying for the result) obscure the art of the puzzle-maker, eh?

Thanks for the suggestion! I've incorporated it into the version in Github "gist": https://gist.github.com/calroc/603ed919bc814ccee10c1b3df6142... (I kept the more verbose query though, as I think the output is nicer. :-) YMMV)

Re: The Power of Prolog

#162

Post by zmonx »

carapace wrote: post #161
zmonx wrote: post #153

Earlier quoted context omitted.

That's one of the most elegant Prolog formulations of this task I have seen so far. Great use of CLP(FD), especially considering that you have only started to learn this technology, as you mentioned in the other thread! I have only two small suggestion: First, since you know that Vars = [GreenHouse, ...] (the Prolog program states this as a constraint), you can simply substitute Vars every time for this list. Therefo…

That's very kind of you. Your comment made my day! :-) I came to Logic Programming via grokking mrocklin's port of Kanren to Python: https://github.com/logpy/logpy ; and to solving logic puzzles via Laws of Form: http://www.markability.net/ (Last year the author of that site George Burnett-Stuart apparently cracked how to encode Predicate Calculus in the notation, which is an exciting development, IMHO!) So I'm not a…

Very, very nice formulation!

You can apply the same trick to the query, i.e., you only need to write down the whole list once, if you formulate the query for example like this:

    ?- Vs = [GreenHouse, RedHouse, IvoryHouse, YellowHouse, BlueHouse,
             Englishman, Spaniard, Ukrainian, Norwegian, Japanese,
             Dog, Snails, Fox, Horse, Zebra,
             Coffee, Tea, Milk, OrangeJuice, Water,
             OldGold, Kools, Chesterfields, LuckyStrike, Parliaments],
       puzzle(Vs),
       label(Vs).
In the above, I have introduced the logical variable Vs to refer to the same list in both goals.

In the case of the Zebra puzzle, we only care about a few of these variables in particular, so we do not even introduce names for others. Instead, we can use anonymous variables, so that not even bindings are reported for those variables that do not matter in this case:

    ?- Vs = [_,_,_,_,_,
             Englishman, Spaniard, Ukrainian, Norwegian, Japanese,
             _,_,_,_,Zebra,
             _,_,_,_,Water|_],
       puzzle(Vs),
       label(Vs).
This yields the following solution:

    Vs = [5, 3, 4, 1, 2, 3, 4, 2, 1|...],
    Englishman = 3,
    Spaniard = 4,
    Ukrainian = 2,
    Norwegian = Water, Water = 1,
    Japanese = Zebra, Zebra = 5 .
By introducing additional variables like this, you can use maplist/2 to more compactly express the sequence of all_distinct/1 constraints.

That's really a very nice way to formulate the puzzle in Prolog, and makes excellent use of features that are still quite recent innovations in Prolog implementations.

Re: The Power of Prolog

#163

Post by zmonx »

arikrak wrote: post #119

Question - is prolog used in the real world? I.e. are there businesses that use prolog in production?

Yes, there are several businesses that use Prolog in production. For example, please see the quotes from the SICStus page, a professional Prolog system (ISO standard compliant) with many commercial applications:

https://www.sics.se/projects/sicstus-prolog-leading-prolog-t...

Here is a salient quote from the article:

"SICStus Prolog is a workhorse in the transport and logistics industries, running systems that handle a third of all airline tickets, and helping railways to operate their trains better."

Further major commercial applications of SICStus Prolog are listed at:

https://sicstus.sics.se/customers.html

These include a voice-operated procedure browser for the International Space Station, and a dispensation order generation algorithm for biological research.

In addition, Prolog is often used in logistics software and for scheduling, among several other tasks for which it is very well suited.

A commercial Prolog's multi-user license easily costs thousands of dollars, so an industrial strength Prolog system is not the kind of software you typically "just buy" as an individual. Typical customers of commercial Prolog systems are other companies, and also universities who buy licenses for research purposes and to teach Prolog.

Re: The Power of Prolog

#164

Post by carapace »

zmonx wrote: post #162
carapace wrote: post #161

Earlier quoted context omitted.

That's very kind of you. Your comment made my day! :-) I came to Logic Programming via grokking mrocklin's port of Kanren to Python: https://github.com/logpy/logpy ; and to solving logic puzzles via Laws of Form: http://www.markability.net/ (Last year the author of that site George Burnett-Stuart apparently cracked how to encode Predicate Calculus in the notation, which is an exciting development, IMHO!) So I'm not a…

Very, very nice formulation! You can apply the same trick to the query, i.e., you only need to write down the whole list once , if you formulate the query for example like this: ?- Vs = [GreenHouse, RedHouse, IvoryHouse, YellowHouse, BlueHouse, Englishman, Spaniard, Ukrainian, Norwegian, Japanese, Dog, Snails, Fox, Horse, Zebra, Coffee, Tea, Milk, OrangeJuice, Water, OldGold, Kools, Chesterfields, LuckyStrike, Parlia…

Cheers! That's awesome. I'm going to set aside some time to learn more Prolog. :-)
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