Comma problem Re: ANSWERS to "What's wrong with XQuery" question

[Michael Kay]

> I think the problem is with lookahead on the grammar level:
>
> "<foo/>  <bar" vs "<foo/>  <bar/>" vs"<foo/>  <bar>  5"
>
> I.e. foo element lower than bar, foo element followed by bar element,
> foo element lower than bar greater than 5. This is not ambiguous, but
> probably requires infinite lookahead.
>
>    

It could be done with an extra-grammatical disambiguation rule not 
unlike many of the rules we already have: if the next thing after the 
">" at the end of a direct constructor is immediately followed by "<", 
treat the "<" as the start of another direct constructor unless it's 
immediately followed by (space, "<", or "="). That's an incompatibility: 
anyone writing (<foo/> <bar) would have to add a space; but we've 
tolerated incompatibilities to highly-implausible constructs in the 
past. No-one writes an element constructor in a context where the result 
has to be immediately atomized.

Michael Kay
Saxonica