scryer-prolog VS swipl-devel

thank you! the scryer community deserves much of the credit too. everyone is welcome and encouraged to join us at https://github.com/mthom/scryer-prolog! some exciting plans in the pipe

Djot is the markup syntax that is used for the documentation of Scryer Prolog, using a parser written in Prolog:

https://github.com/aarroyoc/djota

It works well so far. One of the few limitations I noticed so far pertains to the formatting of tables. For instance, consider the table used in library(format) to describe control sequences:

https://github.com/mthom/scryer-prolog/blob/b0566e41503a6c8d...

It contains several entries that span multiple lines, yet are meant to denote only a single row of the table, such as:

    % | `~Nr`    |  where N is an integer between 2 and 36: format the            |

Still, there are many useful tools based on these ideas, used by programmers and mathematicians alike. What you describe sounds rather like Datalog (e.g. Soufflé Datalog), where you supply some rules and an initial fact, and the system repeatedly expands out the set of facts until nothing new can be derived. (This has to be finite, if you want to get anywhere.) In Prolog (e.g. SWI Prolog) you also supply a set of rules and facts, but instead of a fact as your starting point, you give a query containing some unknown variables, and the system tries to find an assignment of the variables that proves the query. And finally there is a rich array of theorem provers and proof assistants such as Agda, Coq, Lean, and Twelf, which can all be used to help check your reasoning or explore new ideas.

SWIProlog[1] has so far been my go to due to the extensive support system it has. However, I've been meaning to explore higher order logic a bit and Ciao[2] caught my attention there, with sugar for function-like notation and higher order programming including "lambda" style predicate expressions .... and it compiles down to executable. The function notation in this context is along the same lines as Mozart/Oz and can be convenient. Not explore the higher order aspects much though.

[1]: https://www.swi-prolog.org/

[2]: https://en.wikipedia.org/wiki/Ciao_(programming_language)

?- version(). Welcome to SWI-Prolog (threaded, 64 bits, version 9.0.0)SWI-Prolog comes with ABSOLUTELY NO WARRANTY. This is free software. Please run ?- license. for legal details.For online help and background, visit https://www.swi-prolog.org For built-in help, use ?- help(Topic). or ?- apropos(Word). true. ?- del(a, L, [1,2,3]). L = [a, 1, 2, 3] ; L = [1, a, 2, 3] ; L = [1, 2, a, 3] ; L = [1, 2, 3, a] ; false.

$ swipl Welcome to SWI-Prolog (threaded, 64 bits, version 8.5.10) SWI-Prolog comes with ABSOLUTELY NO WARRANTY. This is free software. Please run ?- license. for legal details. For online help and background, visit https://www.swi-prolog.org For built-in help, use ?- help(Topic). or ?- apropos(Word). ?- [fm2gp_primes]. true. ?- time( setup_call_cleanup(open('prolog-primes.txt', write, Out), with_output_to(Out, primes(500_000)), close(Out)) ). % 8,766,852 inferences, 1.055 CPU in 1.198 seconds (88% CPU, 8311018 Lips) Out = (0x600000648100).

The utilities in dgc/bacics.pl that you linked yourself are not too advanced, too quickly. Understanding those is exactly what you need in order to be able to write useful grammars for two reasons. They show how to approach many common issues with DCGs; and you know what building blocks you have at your disposal. I feel you discarded those too fast and strongly suggest you try to revisit them.

- And last but not least... the ability to convert authorization logic into SQL [4]. Which is done by having the language return constraints over any unbound (free) variables.

To me this is what makes logic programming exciting for authorization. It gives you this small kernel of declarative programming, and gives you a ton of freedom to build on top.

[1] https://www.swi-prolog.org/

(Btw. I'm using SWI Prolog.)

Welcome to SWI-Prolog (threaded, 64 bits, version 8.0.2) SWI-Prolog comes with ABSOLUTELY NO WARRANTY. This is free software. Please run ?- license. for legal details. For online help and background, visit http://www.swi-prolog.org For built-in help, use ?- help(Topic). or ?- apropos(Word). ?- use_module(library(lists)). true. ?- clumped([a,a,a,b,b,c], Rs). ERROR: Undefined procedure: clumped/2 (DWIM could not correct goal) ?-

Many library predicates do the argument reordering to take advantage of this special case argument indexing as explained in the answer by u/mycl. For example library(apply) in SWI-Prolog. is full of those.