>>
>> As I understand this particular case, the OP is using a hash not to mark
>> a result as up to date, but rather to mark a side effect (loading data
>> into R) as having taken place. I think this is a misuse of a cache.
>
> It depends on whether one looks at a cache as “a place to store results”
> or “a way to conditionally rerun code blocks only when they change”, I
> suppose. I guess you hold with the former; I think the latter is a
> useful conceptual extension. Knitr (http://yihui.name/knitr/) is a very
> useful literate programming tool for R, and it supports “caching” code
> with side-effects using clever means. I don’t think org should do all
> the tricks knitr does, but it would be useful to be able to
> conditionally reexecute code with no results/with side effects.
>
Could something like the following work? Removing ":results none" and
adding something small as the returned result which may easily be parsed
and placed in the buffer w/o problem.
#+begin_src R :cache yes
# code to perform side effect
x <- 'side effect'
'done'
#+end_src
#+RESULTS[9f4e5b4b07e93c680ab37fc4ba1f75e1bfc0ee0a]:
: done
>
>>
>> What if the R process restarts? The hash would still be valid, but the
>> side effects have been lost.
>
> This is also an issue if the external data files have changed, the RNG
> seed is no longer the same, etc. In such cases, the user has to be
> clever. But the same is true of any cached code that is not a pure
> function.
>
> In practice, if the R process is restarted the “variable not found”
> errors quickly become apparent, and reloading the data is a simple C-u
> C-c C-c away.
>
> (That being said, including the PID of the R process in the results
> hash, to the effect that the code would be rerun in the case you
> mention, might not be a bad idea. But that is a separate discussion.)
This does not need special built in support, e.g.,
#+name: R-pid
#+begin_src sh :var R="/usr/lib64/R/bin/exec/R"
ps auxwww|grep "$R"|grep -v 'grep'|awk '{print $2}'
#+end_src
#+begin_src R :cache yes :var pid=R-pid
# code to perform side effect
x <- 'side effect'
'done'
#+end_src
#+RESULTS[da16f09882a6295815db51247592b77c80ed0056]:
: done
Best,
--
Eric Schulte
http://cs.unm.edu/~eschulte
