Re: [Xsb-development] Re: Var/1 issues?

[David W. <wa...@cs...>]

Bart Demoen writes:
 > 
 > > var/1 does not succeed on attributed variables
 > ...
 > > Does anyone know what other Prologs do?
 > 
 > SICStus:
 > | ?- put_atts(X,a(10)), var(X).
 > true ? 
 > yes
 > 
 > Yap:
 >    ?- put_atts(X,a(10)), var(X).
 > 
 > true ? 
 > yes
 > 
 > SWI - hProlog:
 > ?- put_attr(X,asd,qwe), var(X).
 > 
 > X = _G187{asd = ...} 
 > 
 > Yes
 > ?- 
 > 
 > SWI and hProlog have a new predicate attvar/1 which succeeds for
 > attributed variables, but not for ordinary ones.
 > 
 > Usually, existing code does not break by making var/1 succeed on
 > attributed vars.

Yeah, in XSB var always used to succeed on attributed variables, too.
When I changed the compiler to speed up some conditions, I broke it
for those cases.  So now XSB is inconsistent: if the var is in the
test condition of an if-then(-else), it fails for attributed
variables; in other contexts it succeeds.  Mea culpa.  I'll fix it
immediately.

Thanks Barry and Bart and Terry for doing the debugging I should have
done....

Thanks,
-David