[PPL-devel] [Xsb-development] Arithmetic evaluation bug in the CVS HEAD version of XSB

[Bart Demoen]

> Do you agree with me that the
> behavior I indicated witnesses a (big) XSB bug?

It is more of an inconsistency than a bug: XSB has chosen not to
evaluate variables on the right side of is/2 - Quintus used to do the
same. Long ago, I didn't understand that there are good reasons for
this choice. Now I think that Prolog would be better of without this
feature.

Terry, why does the following not work as a fix in the compiler ? At
compile time, replace X is Y by

	(number(Y) ->
		   X = Y
	;
		   throw(appropriate error)
	)
That would give consistent behaviour, no ? Even though not ISO.
You don't have to do such a thing for </2 (and friends) because of the
rest of XSB's compilation schema for arithmetic ... which has its more
important problems of course:

| ?- -2147483648 < 2147483647 .

++Error[XSB]: [Runtime/C] Overflow in integer, returning MAX_INT

no
| ?- -2147483648 < 1 .

++Error[XSB]: [Runtime/C] Overflow in integer, returning MAX_INT

yes
| ?- -2 < 2147483647 .

no

All the above in XSB Version 3.0.1 (Sagres) of August 7, 2006


Cheers

Bart Demoen