Re: How to dynamically evaluate an equation in the inp

You could also express or transform the expression into Content MathML and
use a processor for that?
https://www.w3.org/TR/MathML3/chapter4.html

On Thu, Jul 15, 2021 at 8:43 AM Dimitre Novatchev dnovatchev@xxxxxxxxx <
xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx> wrote:

> > You can short-circuit the process by generating the lexical analyser and
> syntax analyser directly from a BNF specification
> > using a parser generator; a popular choice in this community is Rex from
> Gunther Rademacher
> > (though this does an excellent job, it suffers from (a) not being
> published as open source, and (b) being poorly documented).
> > A benefit of Rex is that you can generate the parser components as XSLT
> or XQuery code.
>
>
> And a general LR-1 parser written entirely in XSLT has been implemented
> long ago (around 2007 if I remember well) and is part of the FXSL 2.0
> library:
>
> https://github.com/dnovatchev/FXSL-XSLT2/blob/master/f/func-lrParse.xsl
>
> I have used it to parse XPath 2.0 and a subset of JSON:
>
>
> https://github.com/dnovatchev/FXSL-XSLT2/blob/master/newWork/XPathParse1.xsl
>
>
> https://github.com/dnovatchev/FXSL-XSLT2/blob/master/newWork/xpath-parse-test.xsl
>
>
> https://github.com/dnovatchev/FXSL-XSLT2/blob/master/newWork/testFunc-jason-document.xsl
>
> Cheers,
> Dimitre
>
> On Thu, Jul 15, 2021 at 8:28 AM Michael Kay mike@xxxxxxxxxxxx <
> xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx> wrote:
>
>>
>> >
>> > I have XML documents like this:
>> >
>> > <Convert-to-Celsius>
>> >    <equation>(Fahrenheit - 32) * (5/9)</equation>
>> >    <variable>
>> >        <name>Fahrenheit</name>
>> >        <value>32</value>
>> >    </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.
>> >
>>
>> As Dimitre points out, this is an expression (or formula), not an
>> equation.
>>
>> Writing a simple expression interpreter is a common exercise on
>> undergraduate computer science courses, and it's not clear from your
>> question whether you are familiar with the basic principles. The typical
>> solution would be to write a lexical analyser that splits the expression
>> into tokens, then add a syntax analyser to build a syntax tree that
>> represents the grammatical structure of the expression, and then (using the
>> interpreter design pattern) write a depth-first recursive tree walker that
>> evaluates the expression nodes in this tree; the interpreter would have
>> access to a context object that contains the bindings of variables to
>> values, typically as an XDM map.
>>
>> If this description is too terse, then there are plenty of textbooks that
>> explain it in more detail.
>>
>> You can short-circuit the process by generating the lexical analyser and
>> syntax analyser directly from a BNF specification using a parser generator;
>> a popular choice in this community is Rex from Gunther Rademacher (though
>> this does an excellent job, it suffers from (a) not being published as open
>> source, and (b) being poorly documented). A benefit of Rex is that you can
>> generate the parser components as XSLT or XQuery code.
>>
>> Many people in this community would choose to use XPath as the expression
>> language rather than inventing your own. That has the benefit that you
>> don't need to specify and implement the language yourself, it's already
>> been done; and you can then use xsl:evaluate directly for the evaluation.
>>
>> Michael Kay
>> Saxonica
>>
>>
>>
>
> --
> Cheers,
> Dimitre Novatchev
> ---------------------------------------
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