Re: [Xsb-development] all is not well with is/2

[<ki...@cs...>]

Bart Demoen writes:
> 
> > "Limitation" is a very diplomatic word. It is a bug as far as I can see.
> > (Making the system efficient at the expense of correctness.)
> 
> I wouldn't call it a bug. Or not completely a bug.
> I am afraid it was a deliberate decision to comply with old Quintus'
> practice that is now not ISO compliant.

you are right.
But the old Quintus behavior was a bug :-)

From the user point of view it is very non-uniform. One has to remember how
a particular var was bound etc.
For instance, the following "seems" very similar to my previous example:

?- X= -(40), Y is X+1.

but because of the ad hoc decisions on when to eval and when not to the
above will work without any errors.


	--michael