Re: python-mode (python.el): python-backspace

[Stefan Monnier]

>> - delete hungrily all whitespace.
>> - delete to previous level of indentation.
>> Both of those are conceptually mode-independent

> I don't think they are.  Most modes have only a single `valid'
> indentation for any line (according to their indentation rules), and
> it may not be clear how to define a `level of indentation'
> (e.g. Lisp).  That's not the case in Python and Haskell, for instance,
> where deleting a level of indentation is well-defined and either
> meaningful or syntactically invalid.

Hmm... in my world, only Python and Haskell have a notion of a "valid"
indentation.  All others all any indentation whatsoever.  In most modes, it
is true that the syntax is redundant enough that there is little choice
given a particular indentation style, but indentation style is not
always followed, and auto-indentation doesn't always work correctly.
Several major modes use a M-TAB binding to "delete one level of
indentation".  I remember writing a generic "delete to previous level of
indentation" because someone asked for it on gnu.emacs.help...
yes, here it is:

   
http://groups.google.com/groups?selm=5lbrx8e1rc.fsf%40rum.cs.yale.edu&output=gplain

I think binding such a command to DEL makes perfect sense.  But it would be
good to allow modes like python-mode to tune its behavior to be more correct.

>> There is already the "untabify" version of backspace and I think we should
>> make it easier for people to change such things globally.

> What's wrong with `backward-delete-char-untabify-method' for that?

Nothing, other than the fact that it does not include "delete to prev level
of indent".  Oh and that you first have to bind
backward-delete-char-untabify globally and then set the variable (and that
some major modes might then "gratuitously" override the binding locally, of
course).


        Stefan