Re: [RFC] new :post header argument for post-processing of code block results

[Eric Schulte <schulte.eric@gmail.com>]

Aaron Ecay <aaronecay@gmail.com> writes:

> Hi Eric
>
> 2013ko martxoak 31an, Eric Schulte-ek idatzi zuen:
>> 
>> Hi,
>> 
>> I've been wanting to add the ability to post-process the results of a
>> code block for some time, and some recent threads (e.g., [1] and [2])
>> could both have benefited from post-processing of code block output.
>
> This looks very nice!
>
>> 
>> Does this new header argument seem useful?  Any suggestions for better
>> syntax which don't add too much conceptual or code complexity?
>
> See below.
>
>> @@ -625,6 +626,11 @@ block."
>>  				      (not (listp result)))
>>  				 (list (list result)) result))
>>  			   (funcall cmd body params)))
>> +		    ;; possibly perform post process provided its appropriate
>> +		    (when (cdr (assoc :post params))
>> +		      (let ((*this* result))
>> +			(setq result (org-babel-ref-resolve
>> +				      (cdr (assoc :post params))))))
>
> What if you did some string surgery on the :post string, to insert
> ",data=\"the result\"" into the call?  That way users could just write
> :post add-width(width=5cm), which would be automatically transformed
> into add-width(width=5cm,data="[[graph.png]]") before being passed to
> o-b-ref-resolve.
>

I don't like this idea, because then it becomes "magic" which value is
assigned the result of the current code block, rather than the current
case in which it is very explicit.

>
> (I guess you’d have to take special care to handle things like ":post
> no-args()" and ":post no-args" properly, stripping the initial comma in
> the first case and adding parens in the second.)
>
> This requires that all :post code blocks take a data
> argument, but I don’t think that’s more onerous than stipulating the
> *this* variable at the lisp level.
>

I think it is more onerous, I also think it reduces flexibility (the
writing of the called block needs to know exactly which argument will
want to be set by later code blocks).

>
> Also, I’m unclear on whether elisp is supported

Yes it is

> (or should be)

Yes again

> .  Do we want to allow ":post (message *this*)"?

Yes again

If your issue is that (identity *this*) is cumbersome, then I would
agree.  What about if we change `org-babel-read' as with the attached
patch s.t. *any* variable with ear-muffs will be read as Emacs Lisp,
allowing this simpler alternative.

    #+name: val-wrap
    #+begin_src sh :input="" :results verbatim
      echo "--------------------"
      echo "$input"
      echo "--------------------"
    #+end_src

    #+begin_src sh :post val-wrap(input=*this*)
      echo "foo"
    #+end_src

    #+RESULTS:
    : --------------------
    : foo
    : --------------------

Cheers,

-- 
Eric Schulte
http://cs.unm.edu/~eschulte