Re: [O] Fwd: Anyone using or interested in an org to Rmarkdown exporter?

[Charles C. Berry]

On Sat, 1 Nov 2014, John Hendy wrote:

[snip]
> From: John Hendy <address@hidden>
> Date: Fri, Oct 31, 2014 at 7:32 PM
> Subject: Re: [O] Anyone using or interested in an org to Rmarkdown exporter?
> To: Grant Rettke <address@hidden>
>
>
> On Thu, Oct 30, 2014 at 11:37 AM, Grant Rettke <address@hidden> wrote:
> > Good morning,
> >
> > Last week I started learning about [RMarkdown]. It is a [literate
> > programming] tool implemented in, and for, the [ℝ programming
> > language]. Although I haven't dug in deep yet, I do know that (1) it is
> > /basically/ [Markdown] and that (2) `org' exports both to [vanilla
> > markdown] and also [GitHub flavored Markdown] and that (3) a lot of my
> > peers use `RMarkdown' and not `org'. With that that in mind I got
> > curious about what it would take to write an `org2rmarkdown' exporter.
> >
> > The scope of my interest is one-time exports for the most basic and
> > simple `org' document. As such, right now I have no requirements beyond
> > thinking about the opportunity. After doing some Internet searches,
> > there does not seem to be an exporter right now. Questions:
> >
> > • Does one exist and I missed it?
>
> Possibly; at least in some form it does:
> - https://github.com/chasberry/orgmode-accessories/blob/master/ox-ravel.org
>
> > • Do you have any interest in such an exporter?
>
> Yes!
> - https://lists.gnu.org/archive/html/emacs-orgmode/2014-01/msg01436.html
> - https://lists.gnu.org/archive/html/emacs-orgmode/2014-02/msg00291.html
>
> > • Has anyone else ever thought of doing this? If yes, why didn't you?
>
> Yes:
> - Don't know elisp
> - Found the above, which mostly worked. I had to edit my Org file to
> feature a carriage return between text and my lists. ox-ravel appears
> to export literally,

Actually ox-ravel uses derived backends (see the docstring for 
`org-export-define-derived-backend'. Exporting lists and other orgmode 
markup to Rmarkdown is handled by the `md' exporter in ox-md.el.

> and it appears knittr won't pick up a list if
> there's no blank line between regular text and a list.

No, it doesn't. knitr assumes the markdown (or LaTeX or whatever it is 
processing) is correct as written.

> In other words,
> this:
>
> list
> - item1
> - item2
>
> Isn't the same as this:
>
> list
>
> - item1
> - item2

If this is a bug (as it seems), it should probably get a thread with a 
subject line like `org-md-plain-list needs newline' and your example above 
as the ECM.

It is really easy to force `org-md-plain-list' to do this like so:

#+BEGIN_SRC emacs-lisp
  (defun org-md-plain-list (plain-list contents info)
    "Transcode PLAIN-LIST element into Markdown format.
  CONTENTS is the plain-list contents.  INFO is a plist used as
  a communication channel."
    (concat "\n" contents))
#+END_SRC

but this adds vertical padded around nested lists, so something a bit more 
sophisticated is needed.

> Probably a simple enough fix, but just pointing out one nuance that
> org in general and other exporters don't struggle with (they recognize
> a list even with no blank line).

The `md' exporter knows the list is a list - it just doesn't add the 
newline that tells pandoc (or whatever) that the next line could start a 
list.

> > • My guess is that doing an exporter that [builds on an existing
> >   exporter], mentioned above, would be a great start. Thoughts?
> >   • The big difference seems to be control statements passed to the
> >     interpreter, which may or may not be necessary to convert. If not,
> >     than the *stock* `markdown' exporter would provide everything
>
> See if the attached are satisfactory
> - test.org: just a heading, a couple lists, R code (and output), and an image
> - test.Rmd: output of ox-ravel Rmd exporter
> - test.html (well, a screenshot): results of opening test.Rmd in
> RStudio and knitting

Thanks for the example.

Best,

Chuck