Re: Release of CC Mode 5.31

[Alan Mackenzie <acm@muc.de>]

Hi, Richard!

On Sat, 3 Dec 2005, Richard M. Stallman wrote:

>    HEY YOU GUYS (in emacs-devel)!  Is there any chance we could have
>    mapcan (and possibly the other mapping functions in the table on
>    page 85 of the orange Lisp Machine Manual ;-) in the Emacs core for
>    22.1?  Please?  Pretty Please?

>I don't see any great need for mapcan.  It has never been very
>common, and it is easy to do (apply 'nconc (mapcar ...)).

Well, mapcan might be uncommon because it exists only in cl-extra - a
chicken and egg situation.

(apply 'nconc (mapcar ...)) is more difficult to read and understand than
(mapcan ....).  The macros in CC Mode's cc-langs.el and cc-defs.el are
difficult enough to understand, even without this added difficulty.  This
complexity in CC Mode is, I believe, essential rather than frivolous.

>Since I do not have a copy of the Lisp Machine Manual, I do not know
>which other functions you are talking about here.

The "Lisp chine nual" is a work of art, a model of clarity, the epitome
of effective technical writing, and I can recommend it to anybody.  ;-)

The table on page 85 contrasts the various mapping functions according to
how they select the bits of the list to work on, and what they return as
a result.  It looks like this:


                              applies function to

                         |  successive  |   successive  |
                         |   sublists   |    elements   |
          ---------------+--------------+---------------+
              its own    |              |               |
              second     |    map(l)    |    mapc       |
             argument    |              |               |
          ---------------+--------------+---------------+
            list of the  |              |               |
returns      function    |   maplist    |    mapcar     |
              results    |              |               |
          ---------------+--------------+---------------+
            nconc of the |              |               |
              function   |   mapcon     |    mapcan     |
              results    |              |               |
          ---------------+--------------+---------------+

Of these six functions, only mapc and mapcar exist in vanilla Emacs 22.
For the rest, you need to load cl-extra first.  This seems a shame.

-- 
Alan Mackenzie (Munich, Germany)




-------------------------------------------------------
This SF.net email is sponsored by: Splunk Inc. Do you grep through log files
for problems?  Stop!  Download the new AJAX search engine that makes
searching your log files as easy as surfing the  web.  DOWNLOAD SPLUNK!
http://ads.osdn.com/?ad_id=7637&alloc_id=16865&op=click