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Prolog Coding Horror

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Re: Prolog Coding Horror

#11

Post by DonHopkins »

rtpg wrote: post #8

There's something quite illuminating with this first "horror", where they basically say "it's OK to report wrong answers, because you can check the answers". I don't think I've ever felt like it's OK for my program to provide a list of answers where some are right and some are wrong, but reading this... and generally believing in P != NP.... maybe that's a decent way of looking at some stuff!

Sometimes the Biorhythm program on my Apple ][ failed to produce correct answers. But it sure was great for impressing cool hippie chicks.

https://www.youtube.com/watch?v=jYoY1cwAd90

Re: Prolog Coding Horror

#12

Post by hedora »

rtpg wrote: post #8

There's something quite illuminating with this first "horror", where they basically say "it's OK to report wrong answers, because you can check the answers". I don't think I've ever felt like it's OK for my program to provide a list of answers where some are right and some are wrong, but reading this... and generally believing in P != NP.... maybe that's a decent way of looking at some stuff!

The article server is offline, but I assume they found out that prolog rule evaluation depends on the order the rules are presented in the program.

If so, the language they thought they were using (and that they should actually use) is datalog, not prolog.

Datalog has declarative semantics: All facts that are derivable from the base database and the rules will be derived by the interpreter, and it will not add extra hallucinated facts. If that's not true, it's a bug in the runtime, not in the language.

Re: Prolog Coding Horror

#13

Post by bmitch3020 »

appil wrote: post #3

What do people use Prolog for in the real world? I learned about it on a university course and it seems so esoteric compared to other things on the course. Like something invented just for computer scientists to enjoy.

20+ years ago, it was the backend for the business rules engine that processed various logging and monitoring events. The concept was interesting, the performance was terrible, and businesses mostly didn't want to touch it. After I setup clients with a generic set of rules that worked on Prolog facts, most all of my clients were happy to limit their changes to only those fact files.

Re: Prolog Coding Horror

#14

Post by AlotOfReading »

raffael_de wrote: post #10
christophilus wrote: post #4

Earlier quoted context omitted.

Dunno about Prolog, but Datomic uses datalog for its query language, and it’s excellent. Datalog is a subset of Prolog.

What is Datalog used for nowadays?

Other than databases, program analysis. The polonius borrow checker in rustc uses datalog internally.

But you can use it for lots of things. Whenever I'm frustrated with graph based tools being slow (like build systems), I run the graph through a datalog engine for comparison. It's usually much, much faster.

Re: Prolog Coding Horror

#15

Post by Zarathustra30 »

rtpg wrote: post #8

There's something quite illuminating with this first "horror", where they basically say "it's OK to report wrong answers, because you can check the answers". I don't think I've ever felt like it's OK for my program to provide a list of answers where some are right and some are wrong, but reading this... and generally believing in P != NP.... maybe that's a decent way of looking at some stuff!

I've actually run into this in the wild, with regards to sales forecasting. A program we were using returned zero if the error bars on a forecast were over 100%. For example, selling somewhere between 1 and 7 units, but averaging 3.

Returning 3 was "wrong", but infinitely more correct than retuning 0.

Re: Prolog Coding Horror

#17

Post by segmondy »

appil wrote: post #3

What do people use Prolog for in the real world? I learned about it on a university course and it seems so esoteric compared to other things on the course. Like something invented just for computer scientists to enjoy.

Everything, you heard the joke about those who don't know Lisp end up reinventing it, well, the same can be said for Prolog.

Re: Prolog Coding Horror

#19

Post by cwillu »

AdieuToLogic wrote: post #18
mmastrac wrote: post #16

If you want to understand prolog, you must understand the four-port model: https://grack.com/writing/school/enel553/report/prolog.html

And to understand the four-port model is to understand solution-space navigation and pruning.

It's why smartphones lost all their ports: forbidden knowledge must not be leaked to the public.

Re: Prolog Coding Horror

#20

Post by cwillu »

rtpg wrote: post #8

There's something quite illuminating with this first "horror", where they basically say "it's OK to report wrong answers, because you can check the answers". I don't think I've ever felt like it's OK for my program to provide a list of answers where some are right and some are wrong, but reading this... and generally believing in P != NP.... maybe that's a decent way of looking at some stuff!

iirc, shor's algorithm for factoring relies on this.
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