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Ask HN: What's Prolog like in 2024?

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Re: Ask HN: What's Prolog like in 2024?

#91

Post by radomir_cernoch »

GistNoesis wrote: post #76

The "magic" of Prolog is built upon two interesting concepts : Unification ( https://en.wikipedia.org/wiki/Unification_(computer_science)... ) and Backtracking ( https://en.wikipedia.org/wiki/Backtracking ). Often bad teachers only present the declarative aspect of the language. By virtue of being declarative, it allows to express inverse problems in a dangerously simple fashion, but doesn't provide any clue for a so…

Do you see a good way to include backtracking in an imperative programming language?

I can imagine how unification would work, since the ubiquitous "pattern matching" is a special case of Prolog's unification. But I've never seen how backtracking could be useful...

Re: Ask HN: What's Prolog like in 2024?

#92

Post by infinite8s »

drmeister wrote: post #77
tomstuart wrote: post #4

Definitive reference: https://www.urbanautomaton.com/blog/2015/08/10/the-pledge-to...

Dang, substitute Lisp for Prolog and this describes me. Seriously though - Prolog is an awesome tool to have in your toolbox. I've implemented Prolog-like logic programming solutions in several places in my 40+ years of programming. Like rules for assigning molecular mechanics force field atom types.

> Like rules for assigning molecular mechanics force field atom types.

Can you describe a bit more how prolog helped you here? Thanks!

Re: Ask HN: What's Prolog like in 2024?

#93

Post by vmchale »

Girard has some commentary scattered about his writing.

The search algorithms for logic programming are simply slow, it's a very interesting idea in programming languages, but there's a reason it's not widely used.

> PROLOG, its misery. Logic programming was bound to failure, not be- cause of a want of quality, but because of its exaggerations. Indeed, the slogan was something like « pose the question, PROLOG will do the rest ». This paradigm of declarative programming, based on a « generic » algorithmics, is a sort of all-terrain vehicle, capable of doing everything and therefore doing everything badly. It would have been more reasonable to confine PROLOG to tasks for which it is well-adapted, e.g., the maintenance of data bases.

> On the contrary, attempts were made to improve its efficiency. Thus, as systematic search was too costly, « control » primitives, of the style « don’t try this possibility if... » were introduced. And this slogan « logic + control13 », which forgets that the starting point was the logical soundness of the deduction. What can be said of this control which plays against logic14? One recognises the sectarian attitude that we exposed several times: the logic of the idea kills the idea.

> The result is the most inefficient language ever designed; thus, PROLOG is very sensitive to the order in which the clauses (axioms) have been written.

Re: Ask HN: What's Prolog like in 2024?

#94

Post by KingMob »

worldsayshi wrote: post #57
sirwhinesalot wrote: post #56

Earlier quoted context omitted.

Datomic uses Datalog with a weird clojure syntax instead of the usual prolog-like syntax.

Not open source though?

No. It's only free as in beer. There's some weird mention about the Apache 2 license, but it only applies to the binaries, for some odd reason.

Re: Ask HN: What's Prolog like in 2024?

#95

Post by vmchale »

radomir_cernoch wrote: post #91
GistNoesis wrote: post #76

The "magic" of Prolog is built upon two interesting concepts : Unification ( https://en.wikipedia.org/wiki/Unification_(computer_science)... ) and Backtracking ( https://en.wikipedia.org/wiki/Backtracking ). Often bad teachers only present the declarative aspect of the language. By virtue of being declarative, it allows to express inverse problems in a dangerously simple fashion, but doesn't provide any clue for a so…

Do you see a good way to include backtracking in an imperative programming language? I can imagine how unification would work, since the ubiquitous "pattern matching" is a special case of Prolog's unification. But I've never seen how backtracking could be useful...

backtracking is perilous in general; logic programming languages have really nice abilities for such but I don't know how to avoid pathological inefficiency.

Re: Ask HN: What's Prolog like in 2024?

#96

Post by philzook »

klibertp wrote: post #71
mark_l_watson wrote: post #58

Earlier quoted context omitted.

I interviewed and helped hire Mark Thom, the original author of Scryer. I also follow Scryer with interest, even though most of my limited Prolog use has been with SWI Prolog (and one large project with ExperProlog in the 1980s). One thing to check out: Prolog plays fairly well with Python, providing opportunities for hybrid projects.

To playing well with Python, this was on a front page some time ago: https://arxiv.org/abs/2308.15893 "The Janus System: Multi-paradigm Programming in Prolog and Python"

I am quite pleased with the ability to easily use prolog from within python and vice versa. It makes it now one of the easiest and most expressive solvers to plug into for my tastes. I'm starting to accumulate useful solvers here https://github.com/philzook58/prologsolvers/tree/164297d87f6...

You need to install swi prolog https://www.swi-prolog.org/download/stable and pip install janus_swi

A simple example to get started: https://www.swi-prolog.org/pldoc/doc_for?object=section(%27p...

  import janus_swi as janus
  janus.consult("path", """
  edge(a,b).
  edge(b,c).    
  edge(c,d).

  :- table path/2.
  path(X,Y) :- edge(X,Y).
  path(X,Y) :- edge(X,Z), path(Z,Y).
  """)
  list(janus.query("path(a,Y)."))

Re: Ask HN: What's Prolog like in 2024?

#97

Post by phailhaus »

ToucanLoucan wrote: post #79
gorkempacaci wrote: post #52

Prolog, and Constraint Programming especially are great to have in your toolbox. I’ve done research in the field for years, and my job in the industry today is writing Prolog. There are real issues with Prolog: - no proper module nor package system in the modern sense. - in large code bases extra-logical constructs (like cuts) are unavoidable and turn Prolog code into an untenable mess. SWI prolog has single-sided un…

Maybe it's just me but I see a lack of a package manager as a massive, massive pro. I can't stand how seemingly every language has a package manager which requires it's own installation and you have to learn how to use THAT thing and then you need some library off github that does some minor task really well but you can't just download the fucking code, you have to import it via, idk, the Fork-Lyft manager which requ…

You can always just download the code, nobody's forcing you to use a package manager. It just turns out that unless you want to spend most of your life building and fixing other people's code, it's much easier to use the package manager. The inefficiency is the price we pay, but it's worth it.

Re: Ask HN: What's Prolog like in 2024?

#99

Post by jjtheblunt »

chx wrote: post #20
tomstuart wrote: post #4

Definitive reference: https://www.urbanautomaton.com/blog/2015/08/10/the-pledge-to...

> Prolog is not suitable for any problem domain, although this is more readily apparent for some domains than others. Fuckin' A.

what does that mean?

Re: Ask HN: What's Prolog like in 2024?

#100

Post by Normal_gaussian »

dkarl wrote: post #69
greenavocado wrote: post #42

Earlier quoted context omitted.

Prolog and Datalog example (they are identical in this case) % Facts parent(john, mary). parent(mary, ann). parent(mary, tom). % Rules ancestor(X, Y) :- parent(X, Y). ancestor(X, Z) :- parent(X, Y), ancestor(Y, Z). % Query ?- ancestor(john, X). The Prolog code looks identical to Datalog but the execution model is different. Prolog uses depth-first search and backtracking, which can lead to infinite loops if the rules…

> Prolog uses depth-first search and backtracking, which can lead to infinite loops if the rules are not carefully ordered Is this an issue in practice? Most languages can create programs with infinite loops, but it's easy to spot in code reviews. It's been over a decade since I encountered an infinite loop in production in the backend. Just wondering if the same is true for Prolog.

Yes.

It is trivially easy to create loops of rules when describing abstract properties.

Concrete properties tend to have "levels" to them, but many human concepts are self-referential.

In this way, its possible to spot that there may be an issue now or in the future, because the presence or lack of a loop depends on the specific choice of dependencies of a concept. However spotting the potential for a loop doesn't do a lot to help remove its potential existence, or show that it is there or not there.

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