This section describes features for translating input events into
other input events before they become part of key sequences. These
features apply to each event in the order they are described here: each
event is first modified according to extra-keyboard-modifiers,
then translated through keyboard-translate-table (if applicable),
and finally decoded with the specified keyboard coding system. If it is
being read as part of a key sequence, it is then added to the sequence
being read; then subsequences containing it are checked first with
function-key-map and then with key-translation-map.
Each time the user types a keyboard key, it is altered as if the modifier keys specified in the bit mask were held down.
When using a window system, the program can "press" any of the modifier keys in this way. Otherwise, only the CTL and META keys can be virtually pressed.
nil.
If keyboard-translate-table is a char-table, then each character
read from the keyboard is looked up in this character. If the value
found there is non-nil, then it is used instead of the
actual input character.
In the example below, we set keyboard-translate-table to a
char-table. Then we fill it in to swap the characters C-s and
C-\ and the characters C-q and C-^. Subsequently,
typing C-\ has all the usual effects of typing C-s, and vice
versa. (See section Flow Control for more information on this subject.)
(defun evade-flow-control ()
"Replace C-s with C-\ and C-q with C-^."
(interactive)
(setq keyboard-translate-table
(make-char-table 'keyboard-translate-table nil))
;; Swap C-s and C-\.
(aset keyboard-translate-table ?\034 ?\^s)
(aset keyboard-translate-table ?\^s ?\034)
;; Swap C-q and C-^.
(aset keyboard-translate-table ?\036 ?\^q)
(aset keyboard-translate-table ?\^q ?\036))
Note that this translation is the first thing that happens to a
character after it is read from the terminal. Record-keeping features
such as recent-keys and dribble files record the characters after
translation.
keyboard-translate-table to translate
character code from into character code to. It creates
the keyboard translate table if necessary.
The remaining translation features translate subsequences of key
sequences being read. They are implemented in read-key-sequence
and have no effect on input read with read-event.
If function-key-map "binds" a key sequence k to a vector
v, then when k appears as a subsequence anywhere in a
key sequence, it is replaced with the events in v.
For example, VT100 terminals send ESC O P when the
keypad PF1 key is pressed. Therefore, we want Emacs to translate
that sequence of events into the single event pf1. We accomplish
this by "binding" ESC O P to [pf1] in
function-key-map, when using a VT100.
Thus, typing C-c PF1 sends the character sequence C-c
ESC O P; later the function read-key-sequence translates
this back into C-c PF1, which it returns as the vector
[?\C-c pf1].
Entries in 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 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 function-key-map beyond those that can be
deduced from Termcap and Terminfo. See section Terminal-Specific Initialization.
function-key-map
to translate input events into other events. It differs from
function-key-map in two ways:
key-translation-map goes to work after function-key-map is
finished; it receives the results of translation by
function-key-map.
key-translation-map overrides actual key bindings. For example,
if C-x f has a binding in key-translation-map, that
translation takes effect even though C-x f also has a key binding
in the global map.
The intent of key-translation-map is for users to map one
character set to another, including ordinary characters normally bound
to self-insert-command.
You can use function-key-map or 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 read-key-sequence---or 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 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))
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))))
(if (symbolp e)
symbol
(cons symbol (cdr e)))))
(define-key function-key-map "\C-ch" 'hyperify)
Finally, if you have enabled keyboard character set decoding using
set-keyboard-coding-system, decoding is done after the
translations listed above. See section Specifying a Coding System for One Operation. In future
Emacs versions, character set decoding may be done before the other
translations.
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