Re: Release of CC Mode 5.31

[Alan Mackenzie]

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)