Nicolas Goaziou <mail@nicolasgoaziou.fr> writes:

> Rainer M Krug <Rainer@krugs.de> writes:
>
>> That's a pity.
>>
>> It would be really great if one could define different sets of
>> hearer-args and then, at thr beginning of a code block, simply use:
>>
>> #+MACRO: forTangle  :tangle ./test.R :export none
>> #+MACRO: forExecution  :tangle no :export both :session Test14
>> #+MACRO: forNoSession  :tangle no :export both
>
> It might be great. Probably hackish too.
>
> Anyway simplicity of macros is one of its features, IMO. They are
> limited, yet useful for simple things.
>
> Fortunately, there are other ways to achieve what you want without them.
>
>> Would it be difficult to include this feature?
>
> Probably not. The most permissive model for macros is even simpler to
> implement than the current one, i.e., something like
>
>   (replace-regexp-in-string macro-regexp macro-template buffer)
>
> However macros actually follow a different paradigm, in which they are
> required to be parsed. As a consequence they cannot really break the
> structure of their container, which turns them into "safe" tools. For
> example, you can compare the model above and the current one in the
> following document
>
>   A paragraph Paragraph{{{this(arg
>   #+name: table
>   | cell | )}}}  |
>
> Your proposal in to allow them where the parser doesn't look, e.g.,
> Babel header arguments, but probably also other places (node properties,
> keywords...). It is difficult to draw a line. In any case, I'm not sure
> macros would benefit from it. Babel can already do a lot of
> destructuring in a document, not every tool needs to be as versatile as
> Babel.

Thanks for your explanations - I am not using macros regularly (not
yet...) so I was not aware of these aspects.

I was just using macros as an example - I am not advocating to change
macros if this would change something. A simpler option would be
possibly to use properties. Assuming I have the following properties defined:

,----
| #+PROPERTY: headerArgsForTangline :tangle ./testfile.R
| #+PROPERTY: headerArgsForSession :tangle no :session *MyRSession*
| #+PROPERTY: headerArgsForNoSession :tangle no
`----

then I could do

,----
| :header-args*: headerArgsForSession 
`----

and the header arguments would be set to the value of
headerArgsForSession and be ":tangle no :session *MyRSession*".

This would make it possible to define sets of header arguments for
certain aspects (one example I would use it for: creating graphs and
define the width and height properties. Depending if I want portrait or
landscape graphs, I would use the one or the other property and they
could be ca=hanged easily for the whole document.)

Cheers,

Rainer

>
>

-- 
Rainer M. Krug, PhD (Conservation Ecology, SUN), MSc (Conservation Biology, UCT), Dipl. Phys. (Germany)

Centre of Excellence for Invasion Biology
Stellenbosch University
South Africa

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