Should the Prolog query format include the dot?

[guregu]

Question for @triska (or anyone):
Let's say I have a query like:

?- between(1,3,X).

And I loop through the results in Prolog format:

for await (const answer of pl.query(`dif(A, B) ; dif(C, D).`, {format: "prolog"})) {
  console.log(answer);
};
// prints:
// "dif(A,B)."
// "dif(C,D)."

Should these results include the fullstop?
I know that regular toplevels will return something like:

dif(A,B) ;
dif(C,D).

But usually we can't know whether it should end in "." or ";" until we loop again.
I was also thinking that returning a result like foo ; isn't useful because it's a partial term.

I made it optional but I'm not sure whether it'd be better to always exclude it, or always include it.
My rationale for including it is I would like each result (that doesn't write to stdout) to be parsable as a Prolog term.

[triska]

An ideal Prolog toplevel follows a simple basic principle:

1. you put a Prolog term in
2. in response, you get a Prolog term out that is declaratively equivalent to the original query.

I have uploaded a video explaining queries and answers, I hope it is useful: https://youtu.be/UmGih8xOrJ4

Regarding the syntax of terms, we have:

4.148 read-term: A term followed by an end token.
(see 6.2.2, 6.4.8).

end token (* 6.4.8 *)
   = end char (* 6.4.8 *) ;

end char (* 6.4.8 *) = "." ;

Most importantly: It should be completely clear to users whether they must or must not enter ".". Personally, I think a sensible approach is to require users to enter it, and if it is not entered, somehow display an informational text saying for example: "Write '.' at the end of a query."

[triska]

Regarding layout: ; should never be placed at the end of a line, because it looks so similar to , (which usually occurs at the end of a line).

Scryer Prolog and Trealla use an ideal indentation for answers, for example:

?- dif(A,B) ; dif(C, D).
   dif:dif(A,B)
;  dif:dif(C,D).
?- member(X, "abc").
   X = a
;  X = b
;  X = c
;  false.

[guregu]

Thanks a bunch! I'll check out the video 👀
I am learning so much :-)