[babel] Org-babel updates: code block preview, body expand on tangling, row/col-names, and hlines

* [babel] Org-babel updates: code block preview, body expand on tangling, row/col-names, and hlines
@ 2010-04-23 19:00 Eric Schulte
  0 siblings, 0 replies; only message in thread
From: Eric Schulte @ 2010-04-23 19:00 UTC (permalink / raw)
  To: Org Mode

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Hi,

Dan and I have been hard at work putting together the following two
updates to Org-babel.  They introduce both the ability to expand code
blocks according to their header arguments for both previewing and
tangling, and three new header arguments for the handling of column
names, row names, and hlines in tables.

More information is available at the following urls and below:
http://eschulte.github.com/babel-dev/DONE-code-block-body-expansion-for-table-and-preview.html
http://eschulte.github.com/babel-dev/DONE-Handling-of-table-column-names-and-hlines-across-languages-.html

Cheers -- Eric

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** code block body expansion for table and preview

     In org-babel, code is "expanded" prior to evaluation. I.e. the
     code that is actually evaluated comprises the code block
     contents, augmented with the extra code which assigns the
     referenced data to variables. It is now possible to preview
     expanded contents, and also to expand code during during
     tangling.  This expansion takes into account all header
     arguments, and variables.

- preview :: A new key-binding =C-c M-b p= bound to
     `org-babel-expand-src-block' can be used from inside of a source
     code block to preview its expanded contents (which can be very
     useful for debugging).

- tangling :: The expanded body can now be tangled, this includes
     variable values which may be the results of other source-code
     blocks, or stored in headline properties or tables.  One possible
     use for this is to allow those using org-babel for their emacs
     initialization to store values (e.g. usernames, passwords,
     etc...) in headline properties or in tables.

Here is an example of a code block and its resulting expanded body.

The data in the file.
#+tblname: user-data
| username | john-doe |
| password | abc123   |

The actual code block
#+srcname: setup-my-account
#+begin_src emacs-lisp :rownames yes :var data=user-data
  (setq my-special-username (first (first data)))
  (setq my-special-password (first (second data)))
#+end_src

  its expanded contents, as seen with =C-c M-b p=
#+begin_src emacs-lisp
  (let ((data (quote (("john-doe") ("abc123")))))
  (setq my-special-username (first (first data)))
  (setq my-special-password (first (second data)))
  )
#+end_src

** Handling of table column names and hlines across languages 

Org-babel now supports three new header arguments, and new default
behavior for handling horizontal lines in tables (hlines), column
names, and rownames across all languages.  These are as follows

- =:hlines= :: Can take on the values of "yes" or "no", with a default
     value of "no".  These values have the following effects.

     - "no" :: results in all hlines being stripped from the input
          table.  In most languages this is the desired effect, as a
          raw 'hline symbol generally is interpreted as an unbound
          variable and leads to and error.  The following table would
          previously have lead to an error but is now processed as
          shown.

          : #+tblname: many-cols
          : | a | b | c |
          : |---+---+---|
          : | d | e | f |
          : |---+---+---|
          : | g | h | i |
          : 
          : #+source: echo-table
          : #+begin_src python :var tab=many-cols
          :   return tab
          : #+end_src
          : 
          : #+results: echo-table
          : | a | b | c |
          : | d | e | f |
          : | g | h | i |

     - "yes" :: leaves 'hlines in the table. This is the default for
          emacs-lisp which may want to handle hline symbols
          explicitly.

- =:colnames= :: Can take on the values of "yes", "no", or =nil= for
     unassigned.  The default value is =nil=.  These values have the
     following effects

     - =nil= :: If an input table /looks like/ it has column names
          (meaning if it's second row is an hline), then the column
          names will be removed from the table by org-babel before
          processing, then reapplied to the results, so for example
          the following code block has the effect shown.

          : #+tblname: less-cols
          : | a |
          : |---|
          : | b |
          : | c |
          :   
          : #+srcname: echo-table-again
          : #+begin_src python :var tab=less-cols
          :   return [[val + '*' for val in row] for row in tab]
          : #+end_src
          : 
          : #+results: echo-table-again
          : | a  |
          : |----|
          : | b* |
          : | c* |

     - "no" :: No column name pre-processing will take place.

     - "yes" :: Column names are removed and reapplied as with =nil=
          even if the table does not look like it has column names
          (i.e. the second row is not an hline)

- =:rownames= :: Can take on the values of "yes" or "no", with a
     default value of "no".  These values have the following effects.

     - "no" :: No row name pre-processing will take place.

     - "yes" :: The first column of the table is removed from the
          table by org-babel before processing, and is then reapplied
          to the results.  This has the effect shown below.

          : #+tblname: with-rownames
          : | one | 1 | 2 | 3 | 4 |  5 |
          : | two | 6 | 7 | 8 | 9 | 10 | 
          : 
          : #+srcname: echo-table-once-again
          : #+begin_src python :var tab=with-rownames :rownames yes
          :   return [[val + 10 for val in row] for row in tab]            
          : #+end_src
          : 
          : #+results: echo-table-once-again
          : | one | 11 | 12 | 13 | 14 | 15 |
          : | two | 16 | 17 | 18 | 19 | 20 |

	Thanks to Julien Barnier for adding rownames support in R.

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