Prolog Coding Horror(www.metalevel.at)
53 pointsby RohanAdwankar4 hours ago5 comments
  • mmastracan hour ago
    If you want to understand prolog, you must understand the four-port model:

    https://grack.com/writing/school/enel553/report/prolog.html

    • AdieuToLogic37 minutes ago
      And to understand the four-port model is to understand solution-space navigation and pruning.
      • cwillu34 minutes ago
        It's why smartphones lost all their ports: forbidden knowledge must not be leaked to the public.
        • AdieuToLogic3 minutes ago
          > ... forbidden knowledge must not be leaked to the public.

          Understanding is a personal achievement and has nothing to do with "forbidden knowledge" when the source of said knowledge is both quoted above and freely available.

  • rtpg2 hours ago
    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!

    • hedora2 hours ago
      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.

      • cbarrick12 minutes ago
        www.metalevel.at is run by Prolog legend Markus Triska, author of CLP(FD)/CLP(Z).

        So it's not that they "discovered" anything about Prolog; they already knew the language inside out.

        This article explains how to appropriately use Prolog declaratively and with full generality.

    • Zarathustra30an hour ago
      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.

    • cwillu32 minutes ago
      iirc, shor's algorithm for factoring relies on this.
    • DonHopkins2 hours ago
      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

  • appil3 hours ago
    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.
    • AdieuToLogic6 minutes ago
      > What do people use Prolog for in the real world?

      Here[0] is an example of using Ruby and Prolog to solve a real-world AWS management problem.

      0 - https://web.archive.org/web/20190525163234/https://dev.to/da...

    • radomir_cernoch2 hours ago
      Some applications were discussed in https://news.ycombinator.com/item?id=40994552
    • bmitch3020an hour ago
      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.
    • christophilus3 hours ago
      Dunno about Prolog, but Datomic uses datalog for its query language, and it’s excellent. Datalog is a subset of Prolog.
      • ted_dunning2 hours ago
        Datalog may appear to be a subset, but it is quite distinct semantically.
      • raffael_de2 hours ago
        What is Datalog used for nowadays?
        • AlotOfReadingan hour ago
          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.

    • segmondyan hour ago
      Everything, you heard the joke about those who don't know Lisp end up reinventing it, well, the same can be said for Prolog.
    • 2 hours ago
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  • crustycoder3 hours ago
    Mostly overblown.