[Bug 29119] [XP31] xs:error always raises a type error

https://www.w3.org/Bugs/Public/show_bug.cgi?id=29119

--- Comment #14 from Jonathan Robie <jonathan.robie@gmail.com> ---
(In reply to Michael Kay from comment #12)
> A SequenceType does not "describe the type of a value", it
> describes the type of a set of XDM values, and empty sets are perfectly
> legitimate beasts. 

xs:error does not describe the type of an empty set. It does not describe a
type that can occur in an XDM value.  It describes the type of something that a
query can never encounter.

> That doesn't make either expression useless, any more than the integer 0 or the string "" is useless.

The integer 0 and the string "" are types of XDM values that can occur. 
xs:error is not.

The purpose of SequenceType is to describe the types of sets of XDM values. 
When is it useful to have a SequenceType that describes the type of something
that can never exist?  Can you give me an example?

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Received on Tuesday, 6 October 2015 10:37:30 UTC