Joseph Wright wrote:
> J.Fine wrote:
> >> Sorry, I'm a bit lost!  Which bit of the thread are we talking about?
> >> (xparse as-a-concept, post-processing arguments, how to specify
> >> arguments, ... )
> >
> > All of the above, taken together.
> >
> > One starts with parsing key-value arguments in TeX macros, then further
> features are required, and you start adding features to the LaTeX macros
> for list processing and the like, and before you know it something has
> arise that is too complicated for TeX macros.
>
> As I see it, the basic idea of xparse is to separate how user functions
> expect input (stars, optional arguments, mandatory arguments, etc.) from
> how internal functions work (fixed numbers of mandatory arguments). To
> do this, the idea is to create \newcommand-on-steroids, so that complex
> arguments can be processed. For example, \newcommand can't even make two
> optional arguments or look for a star.
>
> So if we take the common example of \section, the code at present mixes
> input syntax and internal workings. The plan would be to replace it with
> something like:
>
> \DeclareDocumentCommand \section { s o m } {
>   % Code here
> }
>
> where the code always has three arguments #1, #2, #3 to pass down to the
> underlying structure. The idea is it is then possible to alter input
> syntax without touching most of the code.

[snip]

There are some interesting ideas here, but why implement them in TeX macros?  How will you translate LaTeX documents into XML?

Surely to do this you will need a LaTeX->XML translator written in /some other language/.  And once you have that, why do you need an implementation written in TeX macros?

And come to that, the translator will surely want access to
> \DeclareDocumentCommand \section { s o m } {
>   % Code here
> }

Perhaps you'll find, when you remove 'TeX macros' from the requirements specification you'll find that it's better not to use TeX macros for the implementation.

--
Jonathan


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