DCG: instantiation_error if the name of a variable bound to a string is not in square brackets

[haijinSk]

A file to consult:

:- use_module(library(dcgs)).

test --> { String = "string" }, String.

A query:

?- phrase(test,S).
   error(instantiation_error,call/2), unexpected.
   S = "string". % expected, but not found.

[UWN]

Shorter:

?- phrase(({S="a"},phrase(S)),L).
   error(instantiation_error,call/2), unexpected.
   S = "a".
?- phrase(({S="a"},S),L).
   idem.
?- S="a",phrase(({S="a"},S),L).
   idem. % even here!!

[UWN]

?- S="a",phrase(S,L).
   idem.

[triska]

Is this addressed by #2738?

[haijinSk]

Now I see here:

#2725 (comment)

example by @adri326

So I'm closing this...

[UWN]

Let me again thank you for reporting the error in the very form you did. I added it as phrase#40 in an even more simplified version. And, as it turns out there are problems with a total of four systems. Identifying such "tiny" problems is one way we can improve the language we love.

[haijinSk]

@UWN Thank you very much. The form of reporting, indicating the unexpected and adding what was expected directly to code examples, I learned it from you.

Yes, when I'm not sure how many and which examples I should include to be informative in the right way, my reporting tends to be more ad hoc, improvisational, trying to be evocative at least.

Not an ideal Prolog user, but I'm "here", slowly here, so to speak; very slowly, nevertheless, to explore, to try, to learn, to be inspired, yes, to love the language and this implementation, incarnation of ideas/perspectives.

Thank you.