Next: Reading One Event, Up: Reading Input
The command loop reads input a key sequence at a time, by calling
read-key-sequence
. Lisp programs can also call this function;
for example, describe-key
uses it to read the key to describe.
This function reads a key sequence and returns it as a string or vector. It keeps reading events until it has accumulated a complete key sequence; that is, enough to specify a non-prefix command using the currently active keymaps.
If the events are all characters and all can fit in a string, then
read-key-sequence
returns a string (see Strings of Events). Otherwise, it returns a vector, since a vector can hold all kinds of events—characters, symbols, and lists. The elements of the string or vector are the events in the key sequence.The argument prompt is either a string to be displayed in the echo area as a prompt, or
nil
, meaning not to display a prompt.In the example below, the prompt ‘?’ is displayed in the echo area, and the user types C-x C-f.
(read-key-sequence "?") ---------- Echo Area ---------- ?C-x C-f ---------- Echo Area ---------- => "^X^F"The function
read-key-sequence
suppresses quitting: C-g typed while reading with this function works like any other character, and does not setquit-flag
. See Quitting.
This is like
read-key-sequence
except that it always returns the key sequence as a vector, never as a string. See Strings of Events.
If an input character is an upper-case letter and has no key binding,
but its lower-case equivalent has one, then read-key-sequence
converts the character to lower case. Note that lookup-key
does
not perform case conversion in this way.
The function read-key-sequence
also transforms some mouse events.
It converts unbound drag events into click events, and discards unbound
button-down events entirely. It also reshuffles focus events and
miscellaneous window events so that they never appear in a key sequence
with any other events.
When mouse events occur in special parts of a window, such as a mode
line or a scroll bar, the event type shows nothing special—it is the
same symbol that would normally represent that combination of mouse
button and modifier keys. The information about the window part is kept
elsewhere in the event—in the coordinates. But
read-key-sequence
translates this information into imaginary
“prefix keys”, all of which are symbols: header-line
,
horizontal-scroll-bar
, menu-bar
, mode-line
,
vertical-line
, and vertical-scroll-bar
. You can define
meanings for mouse clicks in special window parts by defining key
sequences using these imaginary prefix keys.
For example, if you call read-key-sequence
and then click the
mouse on the window's mode line, you get two events, like this:
(read-key-sequence "Click on the mode line: ") => [mode-line (mouse-1 (#<window 6 on NEWS> mode-line (40 . 63) 5959987))]