Re: [xsl] How to dynamically evaluate an equation in the input XML document?

["Liam R. E. Quin liam@xxxxxxxxxxxxxxxx" <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx>]

On Wed, 2021-07-14 at 18:49 +0000, Roger L Costello costello@xxxxxxxxx
wrote:
> Hi Folks,
> 
> I have XML documents like this:
> 
> <Convert-to-Celsius>
> B B B  <equation>(Fahrenheit - 32) * (5/9)</equation>
> B B B  <variable>
> B B B B B B B  <name>Fahrenheit</name>
> B B B B B B B  <value>32</value>
> B B B  </variable>
> </Convert-to-Celsius>
> 
> The document contains an equation which might contain variables. If it
> does contain variables, then I need to fetch their values and replace
> the variables in the equation with their values and then compute the
> value of the equation.
> 
> Have you done this kind of dynamic equation solving using XSLT? If so,
> how did you do it? 

I would probably *not* use fn:evaluate  or saxon:evaluate unless it's 
an XPath expression (doesn't look  like it).

You could use https://www.bottlecaps.de/rex/ to generate a parser for a
simple grammar; this would be much safer than using eval().

The hacky way is to use replace() to change / to div, and to
interpolate variable values, and then use eval(), but make sure there
are no function calls first, as saxon:eval() can execute arbitrary
Java, which can include running external programs, modifying files,
connecting over the network to other systems...

Liam

-- 
Liam Quin,B https://www.delightfulcomputing.com/
Available for XML/Document/Information Architecture/XSLT/
XSL/XQuery/Web/Text Processing/A11Y training, work & consulting.
Barefoot Web-slave, antique illustrations: B http://www.fromoldbooks.org