Re: XPath "none" /type/ not available to the user

On Wednesday 24 May 2006 12:40, Florent Georges wrote:
> Frans Englich wrote:
> > On Wednesday 24 May 2006 11:26, Florent Georges wrote:
> > >   Why is it not available to the user?
> >
> > Probably because no one thought a reasonable usage
> > scenario exists for it(although I don't know for sure).
>
>   A custom error reporting function (based on fn:error()) is
> an enough interesting use case, isn't it?  But more
> generaly, if a system function returns such an absorbent
> type [1], you'll need one time or another to use this type,
> IMHO.

Yes, I guess it is. Will be interesting to see what Michael says if he follows 
up this thread.

You can skip declaring the return type of the function, then the return type 
is inferred from the function body. I agree this is hackish though.

In what scenario does empty-sequence() not work for you? It must be some rare 
cases where empty-sequence() doesn't work and one must use 'none'.

> > I've myself been thinking a bit about this, while writing
> > XQuery test cases.  Try declaring a function with the
> > return type empty-sequence()
>
>   I didn't try to really test it.  Actually, with Saxon
> 8.7.1j we can use every SequenceType (for example xs:string,
> node(), empty-sequence() or text()), even with the '+'
> occurrence indicator.  As if no static type checking was
> made at all.  As if this special case was banned from the
> static type checking engine.

The 'none' type intentionally "disappears" in the type system such that one 
can insert the fn:error() function anywhere without getting a type error.


Cheers,

		Frans