[NTG-context] XML processing instructions

Duncan Hothersall dh at capdm.com
Tue May 3 09:30:33 CEST 2022


Just following up on my own question in case anybody else is interested, I
realised that the logic of my preprocessor code wasn't the problem, it was
just my ignorance of lua and character escaping. Both ? and * are special
characters in string.gsub expressions, so they need to be escaped with the
lua escape character which is % (which sends my editor haywire because it
thinks I am putting in a TeX comment, but never mind!).

So my now working code to translate historic processing instructions into
directives without a separate pass is:

\startluacode
function lxml.preprocessor(data)
 data = string.gsub(data, '<%?capdm %*force_line_stop%?>',
'<?context-directive injector newline ?>')
 return data
end
\stopluacode

\startsetups xml:directive:injector:newline
 \crlf
\stopsetups

Duncan

On Mon, 2 May 2022 at 09:24, Duncan Hothersall <dh at capdm.com> wrote:

> Many thanks Denis. Very useful tip on the injectors and generalised
> command usage. That will definitely come in useful.
>
> My problem is that I already have a lot of XML data with the existing
> processing instructions in it. I know I could use an external preprocess in
> something like Python to change them into injectors before they are fed
> into ConTeXt, but I was hoping there was a way to handle them directly as
> part of the ConTeXt / lua process.
>
> Thanks again though.
>
> Duncan
>
>
>
>
> On Mon, 2 May 2022, 08:48 , <denis.maier at unibe.ch> wrote:
>
>> That was too quick, sorry.
>>
>>
>>
>> Hi Duncan,
>>
>>
>>
>> I have used context’s own injectors for this :
>>
>>
>>
>> <?context-directive injector addlinetopage ?>
>>
>>
>>
>> \startsetups xml:directive:injector:addlinetopage
>>
>>   \adaptlayout[lines=+1]
>>
>> \stopsetups
>>
>>
>>
>> Or, for your line break example :
>>
>>
>>
>> <?context-directive injector newline ?>
>>
>>
>>
>> \startsetups xml:directive:injector:newline
>>
>>   \crlf
>>
>> \stopsetups
>>
>>
>>
>> Also, I have learned that you can just use arbitrary context code in xml:
>>
>>
>>
>> \def\xmltexdirective#1#2{\doif{#1}{command}{#2}}
>>
>>
>>
>> \xmlinstalldirective{tex}{xmltexdirective}
>>
>>
>>
>>          <?context-directive tex command \inframed{xxx} ?>
>>
>>          <?context-directive tex command \page ?>
>>
>>          <?context-directive tex command \crlf ?>
>>
>>
>>
>> Best,
>>
>> Denis
>>
>>
>>
>> *Von:* Maier, Denis Christian (UB)
>> *Gesendet:* Montag, 2. Mai 2022 09:45
>> *An:* 'mailing list for ConTeXt users' <ntg-context at ntg.nl>
>> *Cc:* Duncan Hothersall <dh at capdm.com>
>> *Betreff:* AW: [NTG-context] XML processing instructions
>>
>>
>>
>>
>>
>> *Von:* ntg-context <ntg-context-bounces at ntg.nl> *Im Auftrag von *Duncan
>> Hothersall via ntg-context
>> *Gesendet:* Montag, 2. Mai 2022 09:20
>> *An:* mailing list for ConTeXt users <ntg-context at ntg.nl>
>> *Cc:* Duncan Hothersall <dh at capdm.com>
>> *Betreff:* [NTG-context] XML processing instructions
>>
>>
>>
>> I have a big set of existing XML books (held in a derivative of DocBook)
>> which I'm looking to start processing directly with ConTeXt. (Up to now I
>> have a system which converts the XML into ConTeXt code which is then
>> processed, but this is inefficient and lots of the code is now unsupported.)
>>
>>
>>
>> I've had some success producing output, but my first real sticking point
>> has come with processing instructions. The existing XML contains lots of
>> processing instructions of the form
>>
>> <?capdm whatever?>, some of which can be conditional and introduce new
>> data etc. But I'd be happy at this stage if I could just process the most
>> basic one of them, which is used to introduce a line stop in a running
>> paragraph of text.
>>
>>
>>
>> My best guess at how to do this was to use the lxml.preprocessor function
>> to convert the processing instruction into an element, and then process the
>> element as normal. But (a) my attempt didn't work, and (b) there may
>> well be a better way.
>>
>>
>>
>> Minimal working example below, except that obviously the processing
>> instruction bit doesn't work!
>>
>>
>>
>> Thanks for any help or insights.
>>
>>
>>
>> Duncan
>>
>>
>>
>>
>>
>> MWE:
>>
>> ------
>>
>>
>>
>> \startbuffer[demo]
>> <book>
>>   <para>A paragraph with<?capdm force_line_stop?>a processing
>> instruction.</para>
>> </book>
>> \stopbuffer
>>
>> \startxmlsetups xml:demo:base
>>  \xmlsetsetup{#1}{*}{xml:demo:*}
>> \stopxmlsetups
>> \xmlregisterdocumentsetup{demo}{xml:demo:base}
>>
>> \startxmlsetups xml:demo:book
>>  \xmlflush{#1}
>> \stopxmlsetups
>>
>> \startxmlsetups xml:demo:para
>>  \xmlflush{#1}\endgraf
>> \stopxmlsetups
>>
>> \startluacode
>>  function lxml.preprocessor(data,settings)
>>   return string.find(data,"<?capdm *force_line_stop?>")
>>    and string.gsub(data,"<?capdm
>> *force_line_stop?>","<capdmlinestop></capdmlinestop/>")
>>    or data
>>  end
>> \stopluacode
>>
>> \startxmlsetups xml:demo:capdmlinestop
>>  \crlf
>>  \xmlflush{#1}
>> \stopxmlsetups
>>
>> \setupbodyfont[modern]
>> \starttext
>> \xmlprocessbuffer{demo}{demo}{}
>> \stoptext
>>
>>
>>
>> ------
>>
>

-- 
Duncan Hothersall, Operations Director
CAPDM Limited - Online Program Enablers
0131 677 2400  www.capdm.com
Registered in Scotland: SC168970       VAT: 682 846 983
Registered address: 20 Forth Street Edinburgh EH1 3LH UK
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