[Xpath-ng] List constructor syntax

[David Carlisle]

  Also, if we adopt the XPath 2.0 convention of using an empty list to
  mean an unknown or invalid value,

I'm fairly sure that's a bad convention, one that the xpath2 drafts seem
to have been moving away from as far as possible.

Initially they tried to use () as an "unknown" value and give logical
operators three valued logic sematics using true() false() and ()
but using () as an exceptional value doesn't fit well with the fact that
it's a perfectly normal and expected return value for any path
expression, what used to be called an empty node set...
So later xpath2 drafts seem to be backing off the 3 valued logic idea.


David


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