A compile-time issue with rdf_assert/3

Help!
1

Hey, I get a strange compilation failure with the following code:

:- use_module(library(semweb/rdf11)).

:- rdf_register_prefix(foo, 'https://www.example.com/ontology/foo#').

go :-
    A = a,
    rdf_assert(foo:A, rdf:type, literal(bar)).

when trying to load this file (say from bar.pl), SWI-Prolog version 8.3.27 says:

$ swipl bar.pl
ERROR: /.../bar.pl:5:
ERROR:    Arguments are not sufficiently instantiated
Welcome to SWI-Prolog (threaded, 64 bits, version 8.3.27)
...

?- go.
ERROR: Unknown procedure: go/0 (DWIM could not correct goal)

On the other hand, this works:

:- use_module(library(semweb/rdf11)).

:- rdf_register_prefix(foo, 'https://www.example.com/ontology/foo#').

go :-
    A0 = a,
    A = foo:A0,
    rdf_assert(A, rdf:type, literal(bar)).

If we put the above snippet in foo.pl it loads successfully:

$ swipl -q foo.pl
?- go.
true.

?- rdf(A, B, C).
A = 'https://www.example.com/ontology/foo#a',
B = 'http://www.w3.org/1999/02/22-rdf-syntax-ns#type',
C = "bar"^^'http://www.w3.org/2001/XMLSchema#string'.

I’m not very familiar with the semweb package, but I was very surprised to see an instantiation error before actually executing any query.

So it seems to me to be some term_expansion/2 gone wrong for the argument of rdf_assert/3, maybe?

I’ve tried to look into rdf_expand/4 from semweb/rdf_prefixes.pl as an immediate suspect, but decided to reach out for some help from the experts before digging any deeper.

Is this issue known? is the above workaround adequate?
Thanks!

2

I wasn’t aware. Traditionally rdf_assert/3 only accepted fully ground URLs and relied on compile time expansion. Later we added the option to do the translation also at runtime. I guess the solution would be for the expansion code not to complain. I don’t know whether that is a good or bad idea. It will also stop warnings on e.g. rdfs:Class …

Your work around is fine.