rdf findall error: setup_call_catcher_cleaner

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Richard de Rozario

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Dec 17, 2015, 8:56:59 PM12/17/15
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I get the following error after trying a bagof (or findall) on rdf triples where the triple predicate has a namespace prefix:

ERROR: rdf_db:rdf/3: Type error: `atom' expected, found `foo:rating' (a compound)
^  Exception: (12) setup_call_catcher_cleanup('$bags':'$new_findall_bag', '$bags':findall_loop(_G413, user:rdf(test, foo:rating, _G413), _G342, []), _G481, '$bags':'$destroy_findall_bag') ?

The following example generates this error.

% small rdf program that generates error on bagof
:- use_module(library(semweb/rdf_db)).
:- use_module(library(semweb/rdfs)).
:- rdf_register_prefix(foo,'http://www.foo.org/rdf#',[keep(true)]).


rate(Page,User,Rate):-
  rdf_bnode(B),
  rdf_assert(B,rdfs:member,rdf:'Bag'),
  rdf_assert(Page,foo:rating,B),
  rdf_assert(B,foo:by,User),
  rdf_assert(B,foo:rated,literal(type(integer,Rate))),
  !.

rdfnodes(Sub,Pred,Bags):-
  bagof(B,rdf(Sub,Pred,B),Bags),
  !.

:- rate(test,john,50), rate(test,jane,60).
:- rdfnodes(test,foo:rating,Bags).


The same program without the "foo" prefixes works fine.  Also, doing the bagoff call from the REPL prompt works fine.

Any ideas on how to fix this?

Richard de Rozario

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Dec 17, 2015, 9:21:16 PM12/17/15
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After some further exploring... adding the following as a declaration seems to fix the problem:

:- rdf_meta rdfnodes(r,r,-).

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