Re[2]: Multiple major modes

[Eric M. Ludlam]

>>> Richard Stallman <address@hidden> seems to think that:
>    The use syntax of an overloadable function is similar to programs that
>    call `indent-for-tab-command', or `indent-according-to-mode', but
>    there is no restriction forcing `according-to-mode' as part of the
>    function name.
>
>I understand the similarity, but I see the difference too.
>The source code of `indent-according-to-mode' shows that it
>calls something that can be set differently by different modes.
>
>That's why I prefer using a variable.
>
>However, you didn't show precisely what this feature looks like.
>Perhaps I got the wrong idea of the feature.  Can you show me
>what it looks like?

Hi,

  Here is a use case from semantic, my parsing tool.  This is a
function that would take a name as found in sources, and split it so
that namespaces (if any) and the name are returned.  In many
languages there is nothing special to do, but in C++, it needs to do
something special.  Instead of putting c++ code in the first file, it
is instead placed in a C specific file that contains many C specific
differences.  Of course, the doc string talks about C++, but only as
an example.

  I picked this case because it's very short.


semantic-analyze.el:
--------------------
(define-overload semantic-analyze-split-name (name)
  "Split a tag NAME into a sequence.
Sometimes NAMES are gathered from the parser that are compounded,
such as in C++ where foo::bar means:
  \"The class BAR in the namespace FOO.\"
Return the string NAME for no change, or a list if it needs to be split.")

(defun semantic-analyze-split-name-default (name)
  "Don't split up NAME by default."
  name)
--------------------

As you can see, there is no implementation at the initial
declaration.  In this example, the `-default' is a separate function,
because a body could be given to the original that would wrap either
the `-default' of a mode specific implementation.


semantic-c.el:
--------------
(define-mode-local-override semantic-analyze-split-name c-mode (name)
  "Split up tag names on colon (:) boundaries."
  (let ((ans (split-string name ":")))
    (if (= (length ans) 1)
        name
      (delete "" ans))))
--------------

If you use "C-h f semantic-analyze-split-name RET" you get:

---------------
semantic-analyze-split-name is a compiled Lisp function in 
`semantic-analyze.el'.
(semantic-analyze-split-name name)

This function can be overloaded (see `define-mode-local-override' for details).

Split a tag name into a sequence.
Sometimes NAMES are gathered from the parser that are compounded,
such as in C++ where foo::bar means:
  "The class BAR in the namespace FOO."
Return the string name for no change, or a list if it needs to be split.

[back]
---------------

which would be improved if the doc for individual overloads could be
specified, though I haven't done that yet.  Doing so would make it
much easier to find the implementation actually being run in a
particular case.

I hope this helps.
Eric

-- 
          Eric Ludlam:                 address@hidden, address@hidden
   Home: http://www.ludlam.net            Siege: www.siege-engine.com
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