Prolog looks really useful for solving real world problems. Why doesn't it get used more?
And can you interface to it using Python or some more mainstream languages?
And can you interface to it using Python or some more mainstream languages?
You can and should use logic programming that way. There are libraries for doing e.g. networking and user interfaces with Prolog, but it's not a particularly good fit for that kind of programming.
Many Prolog implementations are quite easy to embed to other languages and there are logic programming embedded languages for most popular programming languages. miniKanren [0] is a popular embeddable logic programming language. There's a chapter about implementing a logic programming environment in Structure and Interpretation of Computer Programs (SICP), which is pretty straightforward.
For my AI courses at the uni years ago, I implemented a simple logic programming environment in Haskell [1]. It was a very fun project and it took me just a few days of work.
[0] http://minikanren.org/ [1] https://github.com/rikusalminen/slolog
That's what I used for my post. There's "Shen Professional" which is a closed source subscription based product getting rapid development http://shenlanguage.org/professional.html
I have not used "Shen Professional" though.
The logic programming language that is used most for real world problems is SQL (the database query language).
Now, SQL may be terrible as a logic programming language (in terms of purity, generality, etc) but it's one of those things where because it's there and it's capacities are good enough for a lot of purposes, it gets used more than tools that one has to go out of one's way to find/use.
Further, note that SQL is widely reviled, partly for it's irregularity but also for the complexity that is inherent to large SQL expressions.
It seems likely to me that if Prolog ever gained the popularity of SQL, there would be umpteen OO packages out there promising to "tame the complexity of Prolog" with one or another OO wrapper, an approach which I assume would leave pure logic programmers aghast.
[1] - https://en.m.wikipedia.org/wiki/Logic_programming [2] - https://en.m.wikipedia.org/wiki/Declarative_programming
If you look at my whole post, I hope it's clear I'm not trying to say SQL is formally anything, just that it's effectively a logic programming language.
IE in an ad-hoc sort-of way SQL can accomplish what a more formal logic programming language accomplish, more or less. You specify a world as a set of tuples and determine whether one set of relations determines another set of relations. That lets you do essentially what prolog can do - for example you can map all the example in the parent article to SQL pretty easily.
How would you map the map coloring example? You can model the color table and the neighbor table in SQL, but that's just the data model. What Prolog also gives you is backtracking search. Is there a good way to do that in SQL? I guess it would work by computing the Cartesian product of states and colors and trying a select on that...
> You specify a world as a set of tuples and determine whether one set of relations determines another set of relations. That lets you do essentially what prolog can do
Datalog, maybe, if you have the search mentioned above. Not Prolog, though: Prolog has terms with free variables and unification. Those have no simple "database" interpretation.
The featured article only shows off a small (non-recursive, negation-free) fragment of a Datalog-like language, which itself is only a small (function-free) fragment of Prolog. You can't make broad claims about Prolog from this small set of examples.
Few people know it, even fewer people like it. It tends to be taught really badly. There are not many recent books, and the old ones teach an outdated pre-ISO-standard language and tend to overemphasize use of the cut (!) operator. Practical aspects needed to build "real-world" systems are almost never discussed. (Interfacing with the operating system in various ways, exceptions and other ways of robust error handling, judicious use of mutable data structures when needed, debugging, profiling, optimization, ...)
But yes, if you get over all these hurdles, it's useful for many things.
> And can you interface to it using Python or some more mainstream languages?
Yes, but you might have to go through foreign function interfaces that are painful from both ends. Or, depending on circumstances, you can just use text files (or pipes) to communicate with an external program written in the other language.
It also didn't help that the Japan project to use Prolog a systems language for a so called 5th generation computer didn't work out.