Re: "user-error: No language for src block: (unnamed)" when running `org-icalendar-combine-agenda-files`

["Charles C. Berry" <ccberry@ucsd.edu>]

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On Fri, 21 Aug 2015, Andreas Leha wrote:

> Hi,
>
> Just a small comment.
>
> [ ... discussion of :caching of evaluation results ... ]
>
>> For purely R-based work, Charles Berry’s ox-ravel package
>> <https://github.com/chasberry/orgmode-accessories/blob/master/ox-ravel.org>
>> is a very interesting approach, since it relies on the cache feature of
>> knitr, which is capable of automatically detecting cross-block
>> dependencies like the example above under some circumstances
>> <http://yihui.name/knitr/demo/cache/>.  It would be interesting to see
>> if that approach could be used to override :cache handling for ob-R,
>> while falling back on org-babel’s less intelligent features for other
>> languages (or in R environments that don’t have knitr available).
>
> That would be just awesome!

I think I understand what Aaron is suggesting, but...

In ox-ravel exports, non-R src blocks get executed as usual, while R 
blocks get converted to `chunks' for later processing by knitr or Sweave 
or whatever. Anything that needs to be communicated from other languages 
to R via noweb `<<run-this()>>' or `:var rvar=elisp-block()' headers 
should work. That is, the resulting chunks will have code put into them 
as usual in R src block execution. (And this is useful for passing latex 
code to R, for example.)

But when the R code is run under knitr or some other engine outside of org 
mode, it cannot communicate values back to src blocks using other 
languages. Or even other R src blocks using `:var rvar=r-src-block()', 
say. And it cannot use `:post' header args. I agree it would be 
interesting to adapt knitr or some other dependency-aware caching engine 
to run under babel control to allow R to push results to other src blocks. 
I don't know how hard it would be to make it work well.

Chuck

p.s. I just pushed an org mode translation of auto-dependson.Rnw from 
https://github.com/yihui/knitr-examples to the ravel-lang branch at
https://github.com/chasberry/orgmode-accessories/blob/ravel-lang/autodep.org
It illustrates automatic dependency-aware caching of R src blocks.

p.p.s. I expect to move the `ravel-lang' branch to `master' soon, so I 
encourage users to try that branch.