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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