[HN Gopher] The Power of Prolog
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The Power of Prolog
Author : fogus
Score : 124 points
Date : 2020-04-07 15:27 UTC (1 days ago)
(HTM) web link (www.metalevel.at)
(TXT) w3m dump (www.metalevel.at)
| collyw wrote:
| Prolog look like it would be the correct tool for the job for a
| certain class of problems, I wish I had time to learn it. I
| always wonder why it doesn't get more attention.
| sacado2 wrote:
| Nowadays, ontology-management systems like Protege and SPARQL
| can more or less solve all problems prolog can solve, while
| providing higher-level formalisms and with the guarantee your
| query will terminate.
| baq wrote:
| i've never used prolog seriously despite having a few
| problems very well suited for declarative solutions -
| variants of job shop scheduling, rule based workflows, etc.
| most reasons for why prolog didn't take off in my job are
| non-technical - it looks weird, it's hard to debug,
| integration with python isn't obvious and one worry i had
| (never tested) was that while the idea is to tell the
| computer about the problem, the real art was placing cuts.
| tejtm wrote:
| Hmm programs terminating because Protege is guaranteed to
| slag your machine is a feature had overlooked.
| Avshalom wrote:
| > I wish I had time to learn it. I always wonder why it doesn't
| get more attention.
|
| pre-answered your own question really. Prolog 'died' in the AI
| winter, so no one knows it and no one knows anyone who knows
| it. Every time you think "huh I bet this is like 100 lines in
| Prolog" it doesn't matter because writing 2000 lines of Java
| (or whatever you know) is still going to be faster than
| learning Prolog.
|
| This is also the problem with literally any comment about
| "using the right tool for the job" with regards to programming
| languages.
| triska wrote:
| Complementing this, neural nets shared the same fate in an AI
| winter, in fact in the AI winter preceding the one you
| mention, and yet they now attract significant attention. In
| large part because the hardware is better, and also because
| the approaches are now better.
|
| We may see analogous developments with Prolog when our
| current hardware gets better or changes its characteristics,
| and when Prolog implementations get better and use better
| approaches that are now becoming available.
|
| I think one difficulty we are facing when judging
| developments in this area is that complex software projects
| such as implementing a Prolog system happen on time scales we
| are not yet used to.
| Avshalom wrote:
| Personally I think Prolog is great* and I'm learning it for
| funsies but neural nets are a specific approach that people
| have been writing in Python, because they already know
| Python. Prolog is a whole thing. Kind of an apples and
| oranges problem.
|
| * I mean seriously it's fantastically expressive: parsing,
| constraint logic, expert systems, database interaction--
| all look and _feel_ completely native, it 's beautiful.
| triska wrote:
| Absolutely, I fully agree!
|
| In fact, I think precisely due to this elementary
| difference, it is reasonable to expect it to take longer
| for Prolog implementations to reach the practical
| applicability we are now seeing in neural networks after
| a few decades of research and improvements.
| [deleted]
| deckard1 wrote:
| I think the reason no one uses Prolog is simply because
| generalized backtracking problems (i.e. the problems you
| would use Prolog for) are too computationally expensive and
| infrequent enough that:
|
| a) You would never train staff or hire experts on Prolog for
| such few problems and...
|
| b) You could probably do much better with a heuristic
| algorithm anyway. Especially on hardware of the day when
| Prolog came out, but even today I imagine this holds true.
|
| Prolog may be useful for quick exploration of a problem
| space. But for code that needs to run frequently, there just
| isn't a great need for what Prolog has to offer.
| girzel wrote:
| I'm guessing because it's so fundamentally different from most
| of the other programming languages out there, which I sometimes
| think are just variations on the variable/function/control flow
| theme (and yes, I've gone fairly far in Lisp).
|
| I've been teaching myself Prolog, and it's sufficiently
| different that I feel like I'm learning to program all over
| again. You can sort of pretend that predicates are just funny
| functions, where you have to put the return value's container
| into the argument list, but that's not really what's going on.
| I loved reading the docs for SWI-Prolog, where most of the
| predicate docstrings start: "True if...". You can say that the
| length predicate returns the length of a list, but really it
| returns true if the given list has a length equal to the given
| integer. It will tell you the length of a list, sure, but it
| will also do the reverse:
|
| ?- length(List, 5) -> List = [_,_,_,_,_]
|
| Nuts!
| agumonkey wrote:
| ever seen Friedman and Byrd talk about kanren ?
| ? evalo(e, 6) (+ 3 3)
| girzel wrote:
| Double nuts!
| galaxyLogic wrote:
| A related question is why do we still have SQL databases when
| everybody could be using Datalog?
|
| https://en.wikipedia.org/wiki/Datalog
| jplane wrote:
| Take a look at datomic, it uses datalog.
| downerending wrote:
| I absolutely loved Prolog and CLP(R) back in the day.
|
| The one thing I never got past was its difficulty in dealing with
| large, mutable sets of data. So, for example, given an array of a
| million or billion elements that are being rapidly modified, even
| the most trivial sorts of backtracking become infeasable. Maybe
| there's some elegant way to do it, but I never got it.
|
| (And difference lists need to die.)
| haolez wrote:
| I've found this channel a few months ago and my wife thinks I'm
| crazy when I'm watching it. "This looks like work, but harder!!".
| Awesome content! Thanks for posting it :)
| triska wrote:
| Thank you so much, and you are welcome! That's an awesome
| slogan!
|
| Some things are hard, yet have no pay-off or are even
| detrimental. On the other hand, things that pay off are often
| proportionally hard.
|
| It is not may goal to make it hard, in fact I am doing
| everything I can to make it as easy as possible. I am very
| interested in didactic approaches, and always welcome feedback!
| I would like to make it worth the effort for viewers, and --
| beyond that -- exceed the required effort in value.
| haolez wrote:
| You do a very good job making it approachable. I'll make a
| PoC this year using Prolog in a specific application
| regarding contract generation (LawTech). It's surely thanks
| to your insights!
|
| Now that I know your handle, I'll ping you when I have some
| news :)
| dang wrote:
| Earlier versions were discussed in 2018:
| https://news.ycombinator.com/item?id=17121028
|
| and 2017: https://news.ycombinator.com/item?id=14045987
|
| (Links are for the curious. Reposts are ok after a year:
| https://news.ycombinator.com/newsfaq.html)
| triska wrote:
| Thank you very much for your interest, I greatly appreciate it!
|
| I hope you are all doing reasonably well. Please take care!
|
| This book was most recently discussed here in May 2018:
|
| https://news.ycombinator.com/item?id=17121028
|
| Since then, I have added a new chapter, _Logical Foundations of
| Prolog_ :
|
| https://www.metalevel.at/prolog/logic
|
| Also, I have made several other additions and improvements. You
| can see most of the changes since the last discussion in a public
| git repository:
|
| https://github.com/triska/the-power-of-prolog/compare/8a94ed...
|
| Currently, I am working on several videos that will eventually
| form the core of the book. Here are a few previews:
|
| https://www.metalevel.at/prolog/videos/logic
|
| https://www.metalevel.at/prolog/videos/timetabling
|
| https://www.metalevel.at/prolog/videos/sparrows_on_eagles
|
| These videos are all work in progress, and they may be replaced
| by better versions at any time. Hence, if possible, please use
| the links above to refer to them: They will always point to the
| latest versions.
|
| Alternatively, please use the following overview page that shows
| all videos:
|
| https://www.metalevel.at/prolog/videos/
|
| Also, I have published a comprehensive journal paper about my
| CLP(B) system, i.e., a _SAT solver_ with some nice algebraic
| properties, seamlessly integrated into Prolog as a specialized
| form of unification:
|
| https://www.metalevel.at/boolean.pdf
|
| For Prolog application programmers and system implementors, the
| paper's appendices may be especially interesting. They formalize
| a few important concepts that are also a major theme in the book.
|
| As of October 2019, the CLP(B) system is also available in Mark
| Thom's Scryer Prolog. Scryer is a Rust-based Prolog
| implementation that is freely available, conforms to the Prolog
| ISO standard, represents strings efficiently as lists of
| characters, and includes important features for implementing
| Prolog-based constraint solvers:
|
| https://github.com/mthom/scryer-prolog
|
| As of a few days ago, Scryer Prolog also ships with my
| implementation of CLP(Z), Constraint Logic Programming over
| _integers_. This is a very useful declarative paradigm for
| solving combinatorial tasks, in some ways superior to SAT solving
| because it allows more convenient modeling, easier
| experimentation with different formulations, and reasoning at a
| higher conceptual level. The chapter on declarative integer
| arithmetic contains more information, and further pointers:
|
| https://www.metalevel.at/prolog/clpz
|
| For illustration, here is an example page where you can solve
| _timetabling instances_ with this approach:
|
| https://www.metalevel.at/prolog/timetabling/
|
| I welcome all comments and suggestions about the book, these
| videos, and Prolog in general. Also, I would like to take this
| opportunity to thank all readers for your thoughtful comments and
| endorsements. Your feedback and encouragement are making this
| work especially worthwhile.
|
| Enjoy!
| wwweston wrote:
| > Scryer is a Rust-based Prolog implementation that is freely
| available
|
| !
|
| As well as an exclamation I suppose that's the cut on my "write
| a prolog to learn rust" predicate, backtracking to finding out
| more about this, especially since I just came across a little
| puzzle for which integer constraint programming is perfect this
| week.
| carapace wrote:
| I want to say _thank you_ , for your book and for all the work
| you're doing promoting and improving Prolog.
| triska wrote:
| You are very welcome!
|
| I greatly enjoy all your postings about your Prolog-based
| interpreter for Joy:
|
| https://osdn.net/projects/joypy/scm/hg/Joypy/blobs/tip/thun/.
| ..
|
| I impulsively upvote this every time I see it. Thank you for
| sharing such an interesting project!
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