Commit f044bf27 authored by Richard M. Stallman's avatar Richard M. Stallman
Browse files

(Translation Keymaps): New node.

Update xrefs from Translating Input to Translation Keymaps.
parent 2410b13a
......@@ -33,6 +33,7 @@ found. The whole process is called @dfn{key lookup}.
* Functions for Key Lookup:: How to request key lookup.
* Changing Key Bindings:: Redefining a key in a keymap.
* Remapping Commands:: Bindings that translate one command to another.
* Translation Keymaps:: Keymaps for translating sequences of events.
* Key Binding Commands:: Interactive interfaces for redefining keys.
* Scanning Keymaps:: Looking through all keymaps, for printing help.
* Menu Keymaps:: Defining a menu as a keymap.
......@@ -642,7 +643,7 @@ only when the mode is used for the first time in a session.
and exit commands. @xref{Intro to Minibuffers}.
Emacs has other keymaps that are used in a different way---translating
events within @code{read-key-sequence}. @xref{Translating Input}.
events within @code{read-key-sequence}. @xref{Translation Keymaps}.
@xref{Standard Keymaps}, for a list of standard keymaps.
......@@ -682,7 +683,7 @@ An error is signaled if @var{key} is not a string or a vector.
@node Searching Keymaps
@section Searching the Active Keymaps
After translation of the input events (@pxref{Translating Input})
After translation of event subsequences (@pxref{Translation Keymaps})
Emacs looks for them in the active keymaps. Here is a pseudo-Lisp
description of the order in which the active keymaps are searched:
......@@ -1472,6 +1473,125 @@ given the current active keymaps. If @var{command} is not remapped
@end defun
@node Translation Keymaps
@section Keymaps for Translating Sequences of Events
This section describes keymaps that are used during reading a key
sequence, to translate certain event sequences into others.
@code{read-key-sequence} checks every subsequence of the key sequence
being read, as it is read, against @code{function-key-map} and then
against @code{key-translation-map}.
@defvar function-key-map
This variable holds a keymap that describes the character sequences sent
by function keys on an ordinary character terminal. This keymap has the
same structure as other keymaps, but is used differently: it specifies
translations to make while reading key sequences, rather than bindings
for key sequences.
If @code{function-key-map} ``binds'' a key sequence @var{k} to a vector
@var{v}, then when @var{k} appears as a subsequence @emph{anywhere} in a
key sequence, it is replaced with the events in @var{v}.
For example, VT100 terminals send @kbd{@key{ESC} O P} when the
keypad @key{PF1} key is pressed. Therefore, we want Emacs to translate
that sequence of events into the single event @code{pf1}. We accomplish
this by ``binding'' @kbd{@key{ESC} O P} to @code{[pf1]} in
@code{function-key-map}, when using a VT100.
Thus, typing @kbd{C-c @key{PF1}} sends the character sequence @kbd{C-c
@key{ESC} O P}; later the function @code{read-key-sequence} translates
this back into @kbd{C-c @key{PF1}}, which it returns as the vector
@code{[?\C-c pf1]}.
Entries in @code{function-key-map} are ignored if they conflict with
bindings made in the minor mode, local, or global keymaps. The intent
is that the character sequences that function keys send should not have
command bindings in their own right---but if they do, the ordinary
bindings take priority.
The value of @code{function-key-map} is usually set up automatically
according to the terminal's Terminfo or Termcap entry, but sometimes
those need help from terminal-specific Lisp files. Emacs comes with
terminal-specific files for many common terminals; their main purpose is
to make entries in @code{function-key-map} beyond those that can be
deduced from Termcap and Terminfo. @xref{Terminal-Specific}.
@end defvar
@defvar key-translation-map
This variable is another keymap used just like @code{function-key-map}
to translate input events into other events. It differs from
@code{function-key-map} in two ways:
@itemize @bullet
@code{key-translation-map} goes to work after @code{function-key-map} is
finished; it receives the results of translation by
Non-prefix bindings in @code{key-translation-map} override actual key
bindings. For example, if @kbd{C-x f} has a non-prefix binding in
@code{key-translation-map}, that translation takes effect even though
@kbd{C-x f} also has a key binding in the global map.
@end itemize
Note however that actual key bindings can have an effect on
@code{key-translation-map}, even though they are overridden by it.
Indeed, actual key bindings override @code{function-key-map} and thus
may alter the key sequence that @code{key-translation-map} receives.
Clearly, it is better to avoid this type of situation.
The intent of @code{key-translation-map} is for users to map one
character set to another, including ordinary characters normally bound
to @code{self-insert-command}.
@end defvar
@cindex key translation function
You can use @code{function-key-map} or @code{key-translation-map} for
more than simple aliases, by using a function, instead of a key
sequence, as the ``translation'' of a key. Then this function is called
to compute the translation of that key.
The key translation function receives one argument, which is the prompt
that was specified in @code{read-key-sequence}---or @code{nil} if the
key sequence is being read by the editor command loop. In most cases
you can ignore the prompt value.
If the function reads input itself, it can have the effect of altering
the event that follows. For example, here's how to define @kbd{C-c h}
to turn the character that follows into a Hyper character:
(defun hyperify (prompt)
(let ((e (read-event)))
(vector (if (numberp e)
(logior (lsh 1 24) e)
(if (memq 'hyper (event-modifiers e))
(add-event-modifier "H-" e))))))
(defun add-event-modifier (string e)
(let ((symbol (if (symbolp e) e (car e))))
(setq symbol (intern (concat string
(symbol-name symbol))))
@end group
(if (symbolp e)
(cons symbol (cdr e)))))
(define-key function-key-map "\C-ch" 'hyperify)
@end group
@end example
If you have enabled keyboard character set decoding using
@code{set-keyboard-coding-system}, decoding is done after the
translations listed above. @xref{Terminal I/O Encoding}. However, in
future Emacs versions, character set decoding may be done at an
earlier stage.
@node Key Binding Commands
@section Commands for Binding Keys
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