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

Subject: Re: [xsl] XPath "none" /type/ not available to the user
From: Florent Georges <darkman_spam@xxxxxxxx>
Date: Wed, 24 May 2006 14:40:47 +0200 (CEST)
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,

> 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.

  [1] I don't know if "absorbent" is the right English word.
      I mean a mathematical property, "for every element in
      a set, using an operation with X will always returns
      X".  For example 0 on R,*.  Here, for every sequence,
      if the static type of one item is "none" then the
      static type of the whole sequence is "none" (I think).




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