Request for xml.filter explanation!

10 Apr 2019

      Hi,

I've the following xml file:

*<?xml version='1.0' standalone='yes?>

<content>
  <object mid="a">
   <text>a paragraph of text</text>
   <value>40.2</value>
  </object>
  <object mid="b">
   <text>another paragraph of text</text>
   <value>10.7</value>
  </object>
  <object mid="c">
   <text>still another paragraph!</text>
   <value>20.5</value>
  </object>
</content>*

And want to calculate the total value of all the objects:

like so:

*\startxmlsetups xml:example:base
   \xmlsetsetup{#1}{content|object}{xml:example:*}
\stopxmlsetups

\xmlregisterdocumentsetup{example}{xml:example:base}

\startxmlsetups xml:example:content
totalvalue: \xmlfunction{#1}{totalvalue}
\xmlflush{#1} \endgraf
\stopxmlsetups

\startxmlsetups xml:example:object
attribute : \xmlatt{#1}{mid} \par
\stopxmlsetups

% LUA

\startluacode
function xml.functions.totalvalue(root)
local score = 0
for e in xml.collected(root,"/object") do
tex.write('Okay!')
--score = score + xml.filter(e,"xml:///value/number()") or 0
end
tex.write(score)
end
\stopluacode

\starttext

\xmlprocessfile{example}{content.xml}{}

\stoptext*

*
*

When I run this example I get:

*totalvalue: Okay!Okay!Okay!0 attribute : a
attribute : b
attribute : c*

That looks allright!

But when I incorporate the line:

*score = score + xml.filter(e,"xml:///value/number()") or 0*

the following Lua error is thrown:
**

*! LuaTeX error [string "\directlua "]:5: attempt to perform arithmetic 
on a nil value*

Has anybody any idea what I'm doing wrong here? The manual 
*xml-mkiv.pdf* doesn't give any clue about this!

Regards,
Gerard
--

Geert Verhaag

Hans Hagen

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