The Power of Prolog

Post by simion314 » Tue, May 22, 2018, 5:38 PM UTC

tabtab wrote: post #136

simion314 wrote: post #118

Earlier quoted context omitted.

Prolog is ideal for some kind of problems, good programmers should know what logic programming is and what problems are perfect for logic programming, then if in real life you hit such a problem you can chose prolog or a library that does logic programming.

I'd like to see a comparison to the alternatives to illustrate objective benefits. I've been down that road before in my-language-can-beat-up-your-language debates, and the end result is usually, "Well, my approach looks easier and simpler TO ME; you just think wrong." Other times they do queries in the app language when they should be using a database.

Post by cousin_it » Tue, May 22, 2018, 5:59 PM UTC

tom_mellior wrote: post #125

cousin_it wrote: post #121

Earlier quoted context omitted.

This Python code does a full search and finds the unique solution instantly: p = 711 q = 711000000 for a in range(1, 1 + p // 4): if q % a == 0: for b in range(a, 1 + (p - a) // 3): if q % (a * b) == 0: for c in range(b, 1 + (p - a - b) // 2): d = p - a - b - c if a * b * c * d == q: print (a, b, c, d) Does Prolog do the same pruning? Alternatively, it could be dumber (omit some of the pruning that my code does) or s…

Prolog doesn't do that automatically, but you can write the same thing in Prolog too: xkcd_ugly(A, B, C, D) :- P = 711, Q = 711000000, Max_A is 1 + P // 4, between(1, Max_A, A), Q mod A =:= 0, Max_B is 1 + (P - A) // 3, between(A, Max_B, B), Q mod (A * B) =:= 0, Max_C is 1 + (P - A - B) // 2, between(B, Max_C, C), D is P - A - B - C, A * B * C * D =:= Q. In SWI-Prolog, I get the following timings: ?- time(xkcd_ugly(A…

Post by triska » Tue, May 22, 2018, 8:25 PM UTC

tom_mellior wrote: post #93

triska wrote: post #44

Earlier quoted context omitted.

Regarding your last sentence: Yes, I can confirm that this has happened, to a reasonable extent of "learned" in the sense that people went on to write programs using this material. However, I do not know how common this is, since I almost exclusively get feedback from those who found the material suitable. There were definitely complete beginners among them. For instance, here is a discussion that happened a few mont…

Cool, good to see others are finding this useful. > In my experience, learning Prolog properly requires dedicated guidance, and it would be highly unusual to achieve mastery without it. There are two readings of this sentence. An unkind spirit might think you are saying that Prolog books cannot make you a master for some inherent reason related to Prolog, independent of any book. Whereas I would say that there is no…

Post by carapace » Tue, May 22, 2018, 10:30 PM UTC

tom_mellior wrote: post #143

carapace wrote: post #139

Earlier quoted context omitted.

Well, the idea that "nobody really uses it in practice" doesn't hold up to the evidence in this thread, eh? It's used and under active development. I think it lacks hype. :-) > Do you think this might be more useful as a module to solve logic puzzles, rather than as a complete language by itself? I was thinking about it this morning and I came to the conclusion that Prolog really is AI. They did it. We have AI alread…

> The Unification algorithm at the heart of Prolog (I'm not an expert!) is pretty much what your brain does when you solve logical puzzles and problems. What makes you think that? I don't think we have a clear idea of what the brain does when doing "intelligent" things, but syntactic unification is very probably not it. For whatever it's worth, the CLP(FD) stuff you posted isn't "just" unification, it needs additiona…

Post by chriswarbo » Tue, May 22, 2018, 11:43 PM UTC

tabtab wrote: post #141

chriswarbo wrote: post #109

Earlier quoted context omitted.

You seem to be moving the goalposts to "why is FP better than X". I was simply pointing out that printf debugging is easy in FP. In fact, it's probably easier in FP, since everything is an expression, whereas imperative languages have a weird expression/statement distinction. For example, if I have code like: buggyCode x y = if foo x then bar x y else baz y I can wrap anything on the right-hand-side in a printf (exce…

That's another thing: "high-meta" languages allow individual developers to re-invent the flow-control wheel in their own image (personal preferences). Consistency is often more important for team readability than factoring (compact code). One man's "clever" can be another's spaghetti code. What works well for individual projects often doesn't scale to larger and often-changing teams.

    renderPage User  page register = page
    renderPage Guest page register = register

    def ifThenElse(c, x, y):
      return {True: x, False: y}[c]

    def renderPage(session, page, register):
      return {User: page, Guest: register}[session]

    class User:
      def renderPage(page, register):
        return page

    class Guest:
      def renderPage(page, register):
        return register