Feature request flag dialect, maybe version and version_data

[ghost]

It seems that scryer prolog has very few Prolog flags:

?- current_prolog_flag(X,Y), write(X-Y), nl, fail; true.
bounded-false
integer_rounding_function-toward_zero
double_quotes-chars
   true.

I am not drumming the ISO core standard drums. I rather observed
that many Prolog systems support the Prolog flag "dialect". Then some
Prolog system also support the Prolog flags "version" and "version_data".

Here is an example from SWI-Prolog:

?- current_prolog_flag(dialect, X).
X = swi.
?- current_prolog_flag(version, X).
X = 80326.
?- current_prolog_flag(version_data, X).
X = swi(8, 3, 26, []).

Would it be possible to add these to Scryer Prolog?

[aarroyoc]

If I remember correctly this was already suggested in #511 and #84. I don't think there is a technical blocker but there are some arguments that is better to not let the programs know which Prolog implementation are they running to encourage standards conformance.

IMO +1 to add them, it could be useful for reporting

[triska]

The notion of "dialect" is alien to the Prolog standard, although it recognizes different levels of conformance to the standard.

You can get the Scryer Prolog version with the internal predicet '$scryer_prolog_version'/1:

v(V) :- '$scryer_prolog_version'(V).

yielding:

?- v(V).
   V = "v0.8.123-596-g72a77 ...".

A better way is to use the -v command line switch:

$ scryer-prolog -v
"v0.8.123-596-g72a7765-modified"

It is bad practice to make code dependent on any specific system: Better test for features such as the existence of predicates, since new Prolog systems that provide these features will then automatically also be supported. You can also add compatibility features you need in your ~/.scryerrc configuration file so that they are loaded on startup, or in a file, say scryer_specific_definitions.pl, and then load that.