Re: [Babel] Interpreting results as tables and (eval)'uation of them

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

Hi Dan,

Dan Amlund Thomsen <danamlund@gmail.com> writes:

> I've encountered some weird, possible buggy, behavior when
> interpreting results as tables (tested with python, scheme and lisp).
>
> * Item 1: Interpreting result as table
> With ":results value" the result is interpreted as a table if
> possible, but with ":results output" it isn't. This happens with
> python, lisp and scheme, but not with c.
>
> The documentation suggests both value and output results should be
> interpreted as a table if possible.
>
> "By default, results are inserted as either a table or scalar
> depending on their value." [http://orgmode.org/manual/results.html]
>
> #+begin_src python :results output
>   print "'(1 2)"
> #+end_src
>
> #+results:
> : '(1 2)
>
> #+begin_src python :results value
>   return "'(1 2)"
> #+end_src
>
> #+results:
> | 1 | 2 |
>

Yes, this assumption (":results output" implies ":results scalar") is
built into many of the language-specific modes and should probably be
removed.

>
> * Item 2: Evaluating list results
> When a result is interpreted as a list, the list is (eval)'ed. This
> happens in non-lisp languages (c, python) but not in lisp languages
> (lisp, scheme).
>
> In my opinion the lists should not be evaluated, but
> 'org-babel-script-escape' and 'org-babel-read' suggests it is intended
> behavior.
>
> Is this a bug or a feature?
>
> #+begin_src c++ :includes <stdio.h>
>   printf("(1 2)");
> #+end_src
>
> Returns the error "Invalid function: 1".
>
> The correct approach is:
> #+begin_src c++ :includes <stdio.h>
>   printf("(list 1 2)");
> #+end_src
>
> #+results:
> | 1 | 2 |
>
> With lisp the list is not evaluated (note that "'(1 2)" results in
> "(1 2)").
> #+begin_src lisp
>   '(1 2)
> #+end_src
>
> #+results:
> | 1 | 2 |
>

Hmm, I'll have to take a closer look at `org-babel-script-escape'.
Automatic evaluation of lispy return strings should not be the default
behavior as I doubt that is what users would expect.  Maybe we shouldn't
be calling `org-babel-read' (which *is* supposed to evaluate lispy
strings) from `org-babel-script-escape'.  Thanks for pointing this out.

>
> * Item 3: Checking if result is a list is not safe
> Mismatched parenthesis and bad characters causes errors. I suggest
> showing the raw result if the result is not a valid list.
>
> I'm not sure if this is a bug or not. These error messages could be
> helpful in debugging code when trying to output a list that needs to
> be evaluated. Although the final output of the (invalid) list could
> also be helpful with debugging.
>
> #+begin_src c++ :includes <stdio.h>
>   printf("(");
> #+end_src
> Returns the error: End of file during parsing
>
> #+begin_src python 
>   return "(list #)"
> #+end_src
> Returns the error: Invalid read syntax: "#"
>

Agreed, in these cases the raw scalar result should be returned.  Again,
thanks for pointing these out.

>
> Here are some possible solutions:
> #+begin_src emacs-lisp
>   (defun org-babel-safe-read-dont-eval (str)
>     "Converts string into a list. Elements are converted into
>   strings to prevent read errors from special characters."
>     (let ((str (replace-regexp-in-string
>                 "\\([^() \f\t\n\r\v]+\\)" "\"\\1\""str)))
>       (condition-case nil
>           (read str)
>         (error (concat "\"" str "\"")))))
>
>   (org-babel-safe-read-dont-eval "(1 1#123 1)")  
> #+end_src
>
> #+results:
> | 1 | 1#123 | 1 |
>
> #+begin_src emacs-lisp
>   (defun org-babel-safe-read-do-eval (str)
>     "Converts string into a evaluated list."
>     (condition-case nil
>         (eval (read str))
>       (error (concat "\"" str "\""))))
>
>   (org-babel-safe-read-do-eval "(1 1#123 1)")
> #+end_src
>
> #+results:
> : "(1 1#123 1)"
>

Yes, these code snippets seem to be headed in the right direction.

Much appreciated -- Eric