Re: [xml-dev] Formulas in XML values

[Rick Jelliffe <rjelliffe@allette.com.au>]

Michael Kay wrote:
>  > I wouldn't say that XPath can't perform rational arithmetic but 
> rather that rational arithmetic is not yet implemented for XPath. 
>  
> XPath does not have an atomic data type that is capable of 
> representing the value 1/3 accurately. You could of course do it all 
> using extension functions, but then it wouldn't really be XPath, just 
> XPath calling out to something else.
>
You could use a sequence (of numbers and delimter/operator strings) and 
eval it. You could then do symbolic simplifications
     ( $a /$b ) + ( $c /$b )  -> ($a + $c) /$b
     $x / 1  ->  $x

It would be simpler in real LISP (can XPath sequences contain 
sequences?) but the same kind of thing.

Cheers
Rick