Request: Prolog Parser

[TrentSe]

Creating an issue for extending universal-ctags to handle Prolog [1].

... as per Masatake's request [2]

[1] https://en.wikipedia.org/wiki/Prolog
[2] #1566 (comment)

[TrentSe]

SWI Prolog syntax grammar/BNF?

http://swi-prolog.996271.n3.nabble.com/SWI-Prolog-syntax-grammar-BNF-td11598.html

[TrentSe]

SWI Prolog provide a clone of Emacs that (I believe*) parses Prolog:

https://www.swi-prolog.org/pldoc/man?section=pceemacs

https://en.wikipedia.org/wiki/SWI-Prolog#PceEmacs

• I haven't used it; I'm familiar with Vim.

[masatake]

Thank you.

I will write an initial minimum version of prolog parser.
I expect you complete it. I would like you to read #2622.
The issue tells how important designing in a parser development is.

Taken from [1]:

/* input.pl */
mother_child(trude, sally).
 
father_child(tom, sally).
father_child(tom, erica).
father_child(mike, tom).
 
sibling(X, Y)      :- parent_child(Z, X), parent_child(Z, Y).
 
parent_child(X, Y) :- father_child(X, Y).
parent_child(X, Y) :- mother_child(X, Y).

What kind of tags output do you expect?
What should be tagged? What "kinds" should be assigned to the tags?

[TrentSe]

Hey Masatake,

Cheers for coming back so quickly. I'll read #2622.

Thanks also for your efforts writing the minimum parser. I'll do what I can to complete it, though will probably need assistance.

[TrentSe]

I'm not that familiar with ctags, so may not answer your question correctly.

Tags:

predicates: mother_child, father_child etc.
atoms: tom, sally,
variables: X, Y

Translation from Prolog speak:

"predicates" -> method (Prolog has no functions)
"atom" -> static value (distinct from a string)
"variable" -> :)

String -> string (text surrounded with ",
for example "this is a SWI-Prolog string"

Text surrounded with ' are treated as an atom.
abc and 'abc' are equivalent.

[TrentSe]

I note that Prolog defines modules [1], for example:

36 :- module(charsio,
37 [ format_to_chars/3, % +Format, +Args, -Codes
38 format_to_chars/4, % +Format, +Args, -Codes, ?Tail
39 write_to_chars/2, % +Term, -Codes
40 write_to_chars/3, % +Term, -Codes, ?Tail
41 atom_to_chars/2, % +Atom, -Codes
42 atom_to_chars/3, % +Atom, -Codes, ?Tail
43 number_to_chars/2, % +Number, -Codes

Is the definition for the module 'charsio' [2].

Predicates listed in the list (from line 37 onwards) are added to the global namespace. Predicates not listed are still accessible, by prepending the module name. For example charsio:some_other_predicate.

Fyi, the number following the predicate name (e.g. atom_to_chars/3) is the arity; it specifies the number of arguments....

[1] https://www.swi-prolog.org/pldoc/man?section=modules
[2] https://www.swi-prolog.org/pldoc/doc/_SWI_/library/charsio.pl?show=src

[TrentSe]

If you have the time, here is a quick intro to Prolog:

https://www.youtube.com/watch?v=SykxWpFwMGs

It's 1 hour long, but you wouldn't need to watch anything like that much to see most of the syntax...

[masatake]

Thank you but prolog knowledge is enough.
Expected tags output is really needed.
It is the area I cannot help you.

[masatake]

Let's focus on smaller input:

mother_child(trude, sally).

What should be tagged?
If we have perfect prolog parser in ctags, which tokens may ctags capture?

[TrentSe]

Here's the syntax doco fro Gnu Prolog:

http://gprolog.org/manual/html_node/gprolog019.html

[TrentSe]

mother_child(trude, sally).

If we have perfect prolog parser in ctags, which tokens may ctags capture?

I'm not that familiar with ctags yet. I can read more to be more helpful.

From what I know now, "mother_child" would be tagged as the equivalent of a C method, trude and sally as the equivalent of C strings.

... would it be helpful for me to write an "equivalent" C program and run it through u-ctags xref...?

My C is rusty, but it would be something like:

void mother_child( "trude", "sally" );

I know this isn't valid C; but trude and sally aren't variables here.

By comparison,

void mother_child( "trude", char *Name ) {
    printf( "%s%n", Name );
}

would be:

mother_child( trude, Name ) :- writeln( Name ).

in Prolog.

[masatake]

O.k. I wrote minimum version of prolog parser.

$ cat input.pl 
mother_child(trude, sally).
$ cat prolog.ctags
--langdef=Prolog
--map-Prolog=.pl
--kinddef-Prolog=p,predicate,predicates
--regex-Prolog=/^([a-zA-Z_]+)\([^.]+\)./\1/p/
$ ./ctags --options=./prolog.ctags --languages=Prolog -o - input.pl 
mother_child	input.pl	/^mother_child(trude, sally).$/;"	p	language:Prolog

Is this the same as what you expect?

[TrentSe]

That was quick!

[TrentSe]

... I also think I see what you're doing. I can build on that...