[NTG-context] Re: XML processing beginner's question

[Hans Hagen via ntg-context <ntg-context@ntg.nl>]

On 8/22/2023 8:53 AM, denis.maier@unibe.ch wrote:
>> -----Ursprüngliche Nachricht-----
>> Von: Hans Hagen via ntg-context <ntg-context@ntg.nl>
>> Gesendet: Montag, 21. August 2023 19:09
>>
>> you need a bit of imagination because basically (depends a bit on what you
>> do) one big nested expansion is going on, as Thomas explained: using setups
>> which are basically macros. The #1 is the current node (but you can store it in a
>> macro and use it later if needed). So, only references are passed around.
>>
>> for thomas: we now also have (in lmtx)
>>
>> \ifxml         {id}{pattern}      \else \fi
>> \ifxmltext     {id}{pattern}      \else \fi
>> \ifxmlatt      {id}{name}{value}  \else \fi
>> \ifxmlattempty {id}{pattern}      \else \fi
>> \ifxmlempty    {id}{pattern}      \else \fi
>> \ifxmlselfempty{id}               \else \fi
> 
> So, these new commands diverge from the older patterns:
> \xmldoifelse{#1}{pattern}{TRUE}{FALSE} ?

they can do the same

> Am I reading this correctly?
These are more 'texie' commands avoiding a middle layer. A main 
difference is that in the case of a \if construction one can have 
lookahead issues when a command in a branch has to look forward and pick 
up an argument but that happens seldom in xml (probably never).

\ifxml{#1}{/foo}
   a
\orelse\ifxml{#1}{/ofo}
   b
\orelse\ifxml{#1}{/oof}
   c
\orelse\ifempty{xmlatt{#1}{n}}
   d
% could also be a check for number first:
\orelse\ifnum\xmlattr{#1}{n}>10\relax % of \norelax
   e
\fi

etc (see lowlevel manual) can look a bit less messy that using 5 nested 
\doifelse's but one has to be aware of the number scanner looking ahead 
so ending up in the branch because setups have no spaces at the end of 
lines.

(kind of) think of it like this:

\protected\def\xmldoifelse#1#2%
   {\ifxml{#1}{pattern}%
      \expandafter\firstoftwoareguments
    \else
      \expandafter\secondoftwoareguments
    \fi}

performance wise there is a bit of a difference but i never hear 
complaints so i guess that matters less

so: just two ways of programming a solution

Hans


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