>Some languages are guaranteed to support left-to-right conditional execution as you outlined in your original message. AFAIK xBASE/VFP is NOT one of them - I don't recall ever seeing any official confirmation of this, either in documentation or by Microsoft. If that's the case there's no need to document this behaviour because you shouldn't be relying on it in the first place.

It's documented in VFP help http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dv_foxhelp9/html/4fcfebe5-0fbe-41da-96ed-ecaa25a6bf23.asp?frame=true :

"Visual FoxPro evaluates logical expressions from left to right, and only for as long as necessary".

It may not be true for the SQL conditions though because query optimizer may rearange them.


>Personally I never use left-to-right conditional execution even in languages that explicitly support it. IMO it makes code hard to understand and is a significant source of nasty bugs. Not to mention that these days, vendors are working hard on optimizing compilers which, if they're at all buggy, will likely have effects like you've seen here. Just say no ;)

I've to disagree with you. I use it all the time. If used properly, it makes code simpler, easier to read and maintain. I never encounter any bugs related to it.