Re: Function for deleting a key binding in a sparse keymap

[Stefan Monnier <monnier@iro.umontreal.ca>]

> It would be good to have a function like this in Emacs:

> (defun delete-key-in-sparse-map(sparse-map key)
>   "In the sparse keymap SPARSE-MAP remove KEY.
> In a sparse keymap if a key is bound to nil that means that
> invoking that key find no binding in that map.  If instead there
> is no binding at all then the default value if any in that keymap
> is used.  This function removes any binding of KEY in the sparse
> keymap SPARSE-MAP so that the default value will be used.

> If SPARSE-MAP is not a sparse keymap an error is raised."

>    ...
>   )

> However I do not know how to implement this for different formats for
> specifying the key.

There is no reason to limit this to sparse keymaps.  AFAIK the problem that
a sparse keymap had all keys bound to nil has been solved.  It seems that
I forgot to update the corresponding documentation.  I've just installed the
patch below.


        Stefan


--- keymaps.texi	22 aoû 2005 10:23:52 -0400	1.68
+++ keymaps.texi	05 déc 2005 14:38:12 -0500	
@@ -158,17 +158,6 @@
 bindings.  A keymap with such a char-table is called a @dfn{full
 keymap}.  Other keymaps are called @dfn{sparse keymaps}.
 
-When a keymap contains a char-table vector, it always defines a
-binding for each character without modifiers.  However, if the binding
-is @code{nil}, it doesn't constitute a definition.  @code{nil} takes
-precedence over a default binding or a binding in the parent keymap.
-So in a full keymap, default bindings are not meaningful for
-characters without modifiers.  They can still apply to characters with
-modifier bits and to non-character events.  A binding of @code{nil}
-does @emph{not} override lower-precedence keymaps; thus, if the local
-map gives a binding of @code{nil}, Emacs uses the binding from the
-global map.
-
 @item @var{string}
 @cindex keymap prompt string
 @cindex overall prompt string
@@ -178,6 +167,13 @@
 use the keymap as a menu.  @xref{Defining Menus}.
 @end table
 
+When the binding is @code{nil}, it doesn't constitute a definition
+but it does take precedence over a default binding or a binding in the
+parent keymap.  On the other hand, a binding of @code{nil} does
+@emph{not} override lower-precedence keymaps; thus, if the local map
+gives a binding of @code{nil}, Emacs uses the binding from the
+global map.
+
 @cindex meta characters lookup
   Keymaps do not directly record bindings for the meta characters.
 Instead, meta characters are regarded for purposes of key lookup as