Re: babel default header args as functions

[rey-coyrehourcq <sebastien.rey-coyrehourcq@univ-rouen.fr>]

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Hi there,

I'm interested by this functionality, do you know if it was merged or i need to apply patch locally ?

Thanks Matt for your work,

Best 
SR

Le mercredi 09 septembre 2020 à 12:33 -0700, Tom Gillespie a écrit :
> Hi Matt,
>    Looking good here. Thanks!
> Tom
> 
> On Wed, Sep 9, 2020 at 12:06 PM Matt Huszagh <huszaghmatt@gmail.com> wrote:
> > Tom Gillespie <tgbugs@gmail.com> writes:
> > 
> > > [...] I have a number of use
> > > cases that I can imagine would benefit greatly from being able to
> > > define a :header-args: :header (lambda () "yay!") property as a
> > > closure (and actually I assumed that it would just work that way if I
> > > tried to do it, clearly not though). I can't tell for sure if the
> > > patch enables this behavior though or whether I would still get a
> > > Wrong type argument error.
> > 
> > This should work. Do you have reason for believing it might not?
> 
> With the patch applied this is working on my end.
> 
> * test header
> :PROPERTIES:
> :header-args:bash: :tangle (lambda () "./from-header.sh")
> :END:
> 
> #+begin_src bash :shebang "#!/usr/bin/env bash"
> echo yes
> #+end_src
> 
> > > [...] Looking
> > > at the patch it seems that it preserves the behavior of performing the
> > > evaluation of the closures at the source block, but I'm not 100% sure.
> > 
> > I'm not sure I completely understand what you mean here. However, the
> > closures are evaluated when point is at the source block, during the
> > source block evaluation, not when the default headers are declared. This
> > allows the closures to use context-dependent functionality (e.g. you can
> > call `org-element-at-point' inside the closure and retrieve whatever
> > information you want). Does this address your concern? Please clarify if
> > I've missed your point.
> 
> Yep, you've got it.
> 
> > > If the default header closures are being evaluated before checking
> > > whether they have been superseded by the headers on a block then that
> > > is incorrect and they should not be evaluated until it is clear that
> > > they are the value of the header for that block and have not been
> > > superseded.
> > 
> > I've fixed my patch (attached) so that now closures are only evaluated
> > when they are used as part of the final set of headers.
> 
> Great.
> 



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