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From: Dan Amlund Thomsen <danamlund@gmail.com>
To: emacs-orgmode@gnu.org
Subject: [Babel] Interpreting results as tables and (eval)'uation of them
Date: Sun, 13 Feb 2011 21:37:45 +0100	[thread overview]
Message-ID: <1297629465.4235.27.camel@eeevk> (raw)

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 |

* 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 |

* 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: "#"

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)"

next             reply	other threads:[~2011-02-13 20:37 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-02-13 20:37 Dan Amlund Thomsen [this message]
2011-02-14 18:58 ` [Babel] Interpreting results as tables and (eval)'uation of them Eric Schulte
2011-03-06 17:59   ` Eric Schulte

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