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This is Info file ../../info/lispref.info, produced by Makeinfo-1.63 from the input file lispref.texi. Edition History: GNU Emacs Lisp Reference Manual Second Edition (v2.01), May 1993 GNU Emacs Lisp Reference Manual Further Revised (v2.02), August 1993 Lucid Emacs Lisp Reference Manual (for 19.10) First Edition, March 1994 XEmacs Lisp Programmer's Manual (for 19.12) Second Edition, April 1995 GNU Emacs Lisp Reference Manual v2.4, June 1995 XEmacs Lisp Programmer's Manual (for 19.13) Third Edition, July 1995 Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995 Free Software Foundation, Inc. Copyright (C) 1994, 1995 Sun Microsystems, Inc. Copyright (C) 1995 Amdahl Corporation. Copyright (C) 1995 Ben Wing. Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that this permission notice may be stated in a translation approved by the Foundation. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided also that the section entitled "GNU General Public License" is included exactly as in the original, and provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that the section entitled "GNU General Public License" may be included in a translation approved by the Free Software Foundation instead of in the original English. File: lispref.info, Node: Interactive Call, Next: Command Loop Info, Prev: Defining Commands, Up: Command Loop Interactive Call ================ After the command loop has translated a key sequence into a definition, it invokes that definition using the function `command-execute'. If the definition is a function that is a command, `command-execute' calls `call-interactively', which reads the arguments and calls the command. You can also call these functions yourself. - Function: commandp OBJECT Returns `t' if OBJECT is suitable for calling interactively; that is, if OBJECT is a command. Otherwise, returns `nil'. The interactively callable objects include strings and vectors (treated as keyboard macros), lambda expressions that contain a top-level call to `interactive', byte-code function objects made from such lambda expressions, autoload objects that are declared as interactive (non-`nil' fourth argument to `autoload'), and some of the primitive functions. A symbol is `commandp' if its function definition is `commandp'. Keys and keymaps are not commands. Rather, they are used to look up commands (*note Keymaps::.). See `documentation' in *Note Accessing Documentation::, for a realistic example of using `commandp'. - Function: call-interactively COMMAND &optional RECORD-FLAG This function calls the interactively callable function COMMAND, reading arguments according to its interactive calling specifications. An error is signaled if COMMAND is not a function or if it cannot be called interactively (i.e., is not a command). Note that keyboard macros (strings and vectors) are not accepted, even though they are considered commands, because they are not functions. If RECORD-FLAG is the symbol `lambda', the interactive calling arguments for `command' are read and returned as a list, but the function is not called on them. If RECORD-FLAG is `t', then this command and its arguments are unconditionally added to the list `command-history'. Otherwise, the command is added only if it uses the minibuffer to read an argument. *Note Command History::. - Function: command-execute COMMAND &optional RECORD-FLAG This function executes COMMAND as an editing command. The argument COMMAND must satisfy the `commandp' predicate; i.e., it must be an interactively callable function or a keyboard macro. A string or vector as COMMAND is executed with `execute-kbd-macro'. A function is passed to `call-interactively', along with the optional RECORD-FLAG. A symbol is handled by using its function definition in its place. A symbol with an `autoload' definition counts as a command if it was declared to stand for an interactively callable function. Such a definition is handled by loading the specified library and then rechecking the definition of the symbol. - Command: execute-extended-command PREFIX-ARGUMENT This function reads a command name from the minibuffer using `completing-read' (*note Completion::.). Then it uses `command-execute' to call the specified command. Whatever that command returns becomes the value of `execute-extended-command'. If the command asks for a prefix argument, it receives the value PREFIX-ARGUMENT. If `execute-extended-command' is called interactively, the current raw prefix argument is used for PREFIX-ARGUMENT, and thus passed on to whatever command is run. `execute-extended-command' is the normal definition of `M-x', so it uses the string `M-x ' as a prompt. (It would be better to take the prompt from the events used to invoke `execute-extended-command', but that is painful to implement.) A description of the value of the prefix argument, if any, also becomes part of the prompt. (execute-extended-command 1) ---------- Buffer: Minibuffer ---------- 1 M-x forward-word RET ---------- Buffer: Minibuffer ---------- => t - Function: interactive-p This function returns `t' if the containing function (the one that called `interactive-p') was called interactively, with the function `call-interactively'. (It makes no difference whether `call-interactively' was called from Lisp or directly from the editor command loop.) If the containing function was called by Lisp evaluation (or with `apply' or `funcall'), then it was not called interactively. The most common use of `interactive-p' is for deciding whether to print an informative message. As a special exception, `interactive-p' returns `nil' whenever a keyboard macro is being run. This is to suppress the informative messages and speed execution of the macro. For example: (defun foo () (interactive) (and (interactive-p) (message "foo"))) => foo (defun bar () (interactive) (setq foobar (list (foo) (interactive-p)))) => bar ;; Type `M-x foo'. -| foo ;; Type `M-x bar'. ;; This does not print anything. foobar => (nil t) File: lispref.info, Node: Command Loop Info, Next: Events, Prev: Interactive Call, Up: Command Loop Information from the Command Loop ================================= The editor command loop sets several Lisp variables to keep status records for itself and for commands that are run. - Variable: last-command This variable records the name of the previous command executed by the command loop (the one before the current command). Normally the value is a symbol with a function definition, but this is not guaranteed. The value is copied from `this-command' when a command returns to the command loop, except when the command specifies a prefix argument for the following command. - Variable: this-command This variable records the name of the command now being executed by the editor command loop. Like `last-command', it is normally a symbol with a function definition. The command loop sets this variable just before running a command, and copies its value into `last-command' when the command finishes (unless the command specifies a prefix argument for the following command). Some commands set this variable during their execution, as a flag for whatever command runs next. In particular, the functions for killing text set `this-command' to `kill-region' so that any kill commands immediately following will know to append the killed text to the previous kill. If you do not want a particular command to be recognized as the previous command in the case where it got an error, you must code that command to prevent this. One way is to set `this-command' to `t' at the beginning of the command, and set `this-command' back to its proper value at the end, like this: (defun foo (args...) (interactive ...) (let ((old-this-command this-command)) (setq this-command t) ...do the work... (setq this-command old-this-command))) - Function: this-command-keys This function returns a vector containing the key and mouse events that invoked the present command, plus any previous commands that generated the prefix argument for this command. (Note: this is not the same as in FSF Emacs, which can return a string.) *Note Events::. This function copies the vector and the events; it is safe to keep and modify them. (this-command-keys) ;; Now use `C-u C-x C-e' to evaluate that. => [#<keypress-event control-U> #<keypress-event control-X> #<keypress-event control-E>] - Variable: last-command-event This variable is set to the last input event that was read by the command loop as part of a command. The principal use of this variable is in `self-insert-command', which uses it to decide which character to insert. This variable is off limits: you may not set its value or modify the event that is its value, as it is destructively modified by `read-key-sequence'. If you want to keep a pointer to this value, you must use `copy-event'. Note that this variable is an alias for `last-command-char' in FSF Emacs. last-command-event ;; Now type `C-u C-x C-e'. => #<keypress-event control-E> - Variable: last-command-char If the value of `last-command-event' is a keyboard event, then this is the nearest ASCII equivalent to it. This the the value that `self-insert-command' will put in the buffer. Remember that there is *not* a 1:1 mapping between keyboard events and ASCII characters: the set of keyboard events is much larger, so writing code that examines this variable to determine what key has been typed is bad practice, unless you are certain that it will be one of a small set of characters. This function exists for compatibility with Emacs version 18. last-command-char ;; Now use `C-u C-x C-e' to evaluate that. => 5 The value is 5 because that is the ASCII code for `C-e'. - Variable: current-mouse-event This variable holds the mouse-button event which invoked this command, or `nil'. This is what `(interactive "e")' returns. - Variable: echo-keystrokes This variable determines how much time should elapse before command characters echo. Its value must be an integer, which specifies the number of seconds to wait before echoing. If the user types a prefix key (say `C-x') and then delays this many seconds before continuing, the key `C-x' is echoed in the echo area. Any subsequent characters in the same command will be echoed as well. If the value is zero, then command input is not echoed. File: lispref.info, Node: Events, Next: Reading Input, Prev: Command Loop Info, Up: Command Loop Events ====== The XEmacs command loop reads a sequence of "events" that represent keyboard or mouse activity. Unlike in Emacs 18 and in FSF Emacs, events are a primitive Lisp type that must be manipulated using their own accessor and settor primitives. This section describes the representation and meaning of input events in detail. A key sequence that starts with a mouse event is read using the keymaps of the buffer in the window that the mouse was in, not the current buffer. This does not imply that clicking in a window selects that window or its buffer--that is entirely under the control of the command binding of the key sequence. For information about how exactly the XEmacs command loop works, *Note Reading Input::. - Function: eventp OBJECT This function returns non-`nil' if EVENT is an input event. * Menu: * Event Types:: Events come in different types. * Event Contents:: What the contents of each event type are. * Event Predicates:: Querying whether an event is of a particular type. * Accessing Mouse Event Positions:: Determining where a mouse event occurred, and over what. * Accessing Other Event Info:: Accessing non-positional event info. * Working With Events:: Creating, copying, and destroying events. * Converting Events:: Converting between events, keys, and characters. File: lispref.info, Node: Event Types, Next: Event Contents, Up: Events Event Types ----------- Events represent keyboard or mouse activity or status changes of various sorts, such as process input being available or a timeout being triggered. The different event types are as follows: key-press event A key was pressed. Note that modifier keys such as "control", "shift", and "alt" do not generate events; instead, they are tracked internally by XEmacs, and non-modifier key presses generate events that specify both the key pressed and the modifiers that were held down at the time. button-press event button-release event A button was pressed or released. Along with the button that was pressed or released, button events specify the modifier keys that were held down at the time and the position of the pointer at the time. pointer-motion event The pointer was moved. Along with the position of the pointer, these events also specify the modifier keys that were held down at the time. misc-user event A menu item was selected, or the scrollbar was used. process event Input is available on a process. timeout event A timeout has triggered. magic event Some window-system-specific action (such as a frame being resized or a portion of a frame needing to be redrawn) has occurred. The contents of this event are not accessible at the E-Lisp level, but `dispatch-event' knows what to do with an event of this type. eval event This is a special kind of event specifying that a particular function needs to be called when this event is dispatched. An event of this type is sometimes placed in the event queue when a magic event is processed. This kind of event should generally just be passed off to `dispatch-event'. *Note Dispatching an Event::. File: lispref.info, Node: Event Contents, Next: Event Predicates, Prev: Event Types, Up: Events Contents of the Different Types of Events ----------------------------------------- Every event, no matter what type it is, contains a timestamp (which is typically an offset in milliseconds from when the X server was started) indicating when the event occurred. In addition, many events contain a "channel", which specifies which frame the event occurred on, and/or a value indicating which modifier keys (shift, control, etc.) were held down at the time of the event. The contents of each event are as follows: key-press event channel timestamp key Which key was pressed. This is an integer (in the printing ASCII range: >32 and <127) or a symbol such as `left' or `right'. Note that many physical keys are actually treated as two separate keys, depending on whether the shift key is pressed; for example, the "a" key is treated as either "a" or "A" depending on the state of the shift key, and the "1" key is similarly treated as either "1" or "!" on most keyboards. In such cases, the shift key does not show up in the modifier list. For other keys, such as `backspace', the shift key shows up as a regular modifier. modifiers Which modifier keys were pressed. As mentioned above, the shift key is not treated as a modifier for many keys and will not show up in this list in such cases. button-press event button-release event channel timestamp button What button went down or up. Buttons are numbered starting at 1. modifiers Which modifier keys were pressed. The special business mentioned above for the shift key does *not* apply to mouse events. x y The position of the pointer (in pixels) at the time of the event. pointer-motion event channel timestamp x y The position of the pointer (in pixels) after it moved. modifiers Which modifier keys were pressed. The special business mentioned above for the shift key does *not* apply to mouse events. misc-user event timestamp function The E-Lisp function to call for this event. This is normally either `eval' or `call-interactively'. object The object to pass to the function. This is normally the callback that was specified in the menu description. process_event timestamp process The Emacs "process" object in question. timeout event timestamp function The E-Lisp function to call for this timeout. It is called with one argument, the event. object Some Lisp object associated with this timeout, to make it easier to tell them apart. The function and object for this event were specified when the timeout was set. magic event timestamp (The rest of the information in this event is not user-accessible.) eval event timestamp function An E-Lisp function to call when this event is dispatched. object The object to pass to the function. The function and object are set when the event is created. File: lispref.info, Node: Event Predicates, Next: Accessing Mouse Event Positions, Prev: Event Contents, Up: Events Event Predicates ---------------- The following predicates return whether an object is an event of a particular type. - Function: button-event-p OBJECT OBJECT This is true if OBJECT is a button-press or button-release event. - Function: button-press-event-p OBJECT This is true if OBJECT is a mouse-button-press event. - Function: button-release-event-p OBJECT This is true if OBJECT is a mouse-button-release event. - Function: eval-event-p OBJECT This is true if OBJECT is an eval or misc-user event. - Function: key-press-event-p OBJECT This is true if OBJECT is a key-press event. - Function: misc-user-event-p OBJECT This is true if OBJECT is a misc-user event. - Function: motion-event-p OBJECT This is true if OBJECT is a mouse-motion event. - Function: process-event-p OBJECT This is true if OBJECT is a process event. - Function: timeout-event-p OBJECT This is true if OBJECT is a timeout event. - Function: event-live-p OBJECT This is true if OBJECT is any event that has not been deallocated. File: lispref.info, Node: Accessing Mouse Event Positions, Next: Accessing Other Event Info, Prev: Event Predicates, Up: Events Accessing the Position of a Mouse Event --------------------------------------- Unlike other events, mouse events (i.e. mouse-motion, button-press, and button-release events) occur in a particular location on the screen. Many primitives are provided for determining exactly where the event occurred and what is under that location. * Menu: * Frame-Level Event Position Info:: * Window-Level Event Position Info:: * Event Text Position Info:: * Event Glyph Position Info:: * Event Toolbar Position Info:: * Other Event Position Info:: File: lispref.info, Node: Frame-Level Event Position Info, Next: Window-Level Event Position Info, Up: Accessing Mouse Event Positions Frame-Level Event Position Info ............................... The following functions return frame-level information about where a mouse event occurred. - Function: event-frame EVENT This function returns the "channel" or frame that the given mouse motion, button press, or button release event occurred in. This will be `nil' for non-mouse events. - Function: event-x-pixel EVENT This function returns the X position in pixels of the given mouse event. The value returned is relative to the frame the event occurred in. This will signal an error if the event is not a mouse-motion, button-press, or button-release event. - Function: event-y-pixel EVENT This function returns the Y position in pixels of the given mouse event. The value returned is relative to the frame the event occurred in. This will signal an error if the event is not a mouse-motion, button-press, or button-release event. File: lispref.info, Node: Window-Level Event Position Info, Next: Event Text Position Info, Prev: Frame-Level Event Position Info, Up: Accessing Mouse Event Positions Window-Level Event Position Info ................................ The following functions return window-level information about where a mouse event occurred. - Function: event-window EVENT Given a mouse motion, button press, or button release event, compute and return the window on which that event occurred. This may be `nil' if the event occurred in the border or over a toolbar. The modeline is considered to be in the window it represents. - Function: event-buffer EVENT Given a mouse motion, button press, or button release event, compute and return the buffer of the window on which that event occurred. This may be `nil' if the event occurred in the border or over a toolbar. The modeline is considered to be in the window it represents. This is equivalent to calling `event-window' and then calling `event-buffer' on the result if it is a window. - Function: event-window-x-pixel EVENT This function returns the X position in pixels of the given mouse event. The value returned is relative to the window the event occurred in. This will signal an error if the event is not a mouse-motion, button-press, or button-release event. - Function: event-window-y-pixel EVENT This function returns the Y position in pixels of the given mouse event. The value returned is relative to the window the event occurred in. This will signal an error if the event is not a mouse-motion, button-press, or button-release event. File: lispref.info, Node: Event Text Position Info, Next: Event Glyph Position Info, Prev: Window-Level Event Position Info, Up: Accessing Mouse Event Positions Event Text Position Info ........................ The following functions return information about the text (including the modeline) that a mouse event occurred over or near. - Function: event-over-text-area-p EVENT Given a mouse-motion, button-press, or button-release event, this function returns `t' if the event is over the the text area of a window. Otherwise, `nil' is returned. The modeline is not considered to be part of the text area. - Function: event-over-modeline-p EVENT Given a mouse-motion, button-press, or button-release event, this function returns `t' if the event is over the modeline of a window. Otherwise, `nil' is returned. - Function: event-x EVENT This function returns the X position of the given mouse-motion, button-press, or button-release event in characters. This is relative to the window the event occurred over. - Function: event-y EVENT This function returns the Y position of the given mouse-motion, button-press, or button-release event in characters. This is relative to the window the event occurred over. - Function: event-point EVENT This function returns the character position of the given mouse-motion, button-press, or button-release event. If the event did not occur over a window, or did not occur over text, then this returns `nil'. Otherwise, it returns an index into the buffer visible in the event's window. - Function: event-closest-point EVENT This function returns the character position of the given mouse-motion, button-press, or button-release event. If the event did not occur over a window or over text, it returns the closest point to the location of the event. If the Y pixel position overlaps a window and the X pixel position is to the left of that window, the closest point is the beginning of the line containing the Y position. If the Y pixel position overlaps a window and the X pixel position is to the right of that window, the closest point is the end of the line containing the Y position. If the Y pixel position is above a window, 0 is returned. If it is below a window, the value of `(window-end)' is returned. File: lispref.info, Node: Event Glyph Position Info, Next: Event Toolbar Position Info, Prev: Event Text Position Info, Up: Accessing Mouse Event Positions Event Glyph Position Info ......................... The following functions return information about the glyph (if any) that a mouse event occurred over. - Function: event-over-glyph-p EVENT Given a mouse-motion, button-press, or button-release event, this function returns `t' if the event is over a glyph. Otherwise, `nil' is returned. - Function: event-glyph-extent EVENT If the given mouse-motion, button-press, or button-release event happened on top of a glyph, this returns its extent; else `nil' is returned. - Function: event-glyph-x-pixel EVENT Given a mouse-motion, button-press, or button-release event over a glyph, this function returns the X position of the pointer relative to the upper left of the glyph. If the event is not over a glyph, it returns `nil'. - Function: event-glyph-y-pixel EVENT Given a mouse-motion, button-press, or button-release event over a glyph, this function returns the Y position of the pointer relative to the upper left of the glyph. If the event is not over a glyph, it returns `nil'. File: lispref.info, Node: Event Toolbar Position Info, Next: Other Event Position Info, Prev: Event Glyph Position Info, Up: Accessing Mouse Event Positions Event Toolbar Position Info ........................... - Function: event-over-toolbar-p EVENT Given a mouse-motion, button-press, or button-release event, this function returns `t' if the event is over a toolbar. Otherwise, `nil' is returned. - Function: event-toolbar-button EVENT If the given mouse-motion, button-press, or button-release event happened on top of a toolbar button, this function returns the button. Otherwise, `nil' is returned. File: lispref.info, Node: Other Event Position Info, Prev: Event Toolbar Position Info, Up: Accessing Mouse Event Positions Other Event Position Info ......................... - Function: event-over-border-p EVENT Given a mouse-motion, button-press, or button-release event, this function returns `t' if the event is over an internal toolbar. Otherwise, `nil' is returned. File: lispref.info, Node: Accessing Other Event Info, Next: Working With Events, Prev: Accessing Mouse Event Positions, Up: Events Accessing the Other Contents of Events -------------------------------------- The following functions allow access to the contents of events other than the position info described in the previous section. - Function: event-timestamp EVENT This function returns the timestamp of the given event object. - Function: event-device EVENT This function returns the device that the given event occurred on. - Function: event-key EVENT This function returns the KeySym of the given key-press event. This will be the ASCII code of a printing character, or a symbol. - Function: event-button EVENT This function returns the button-number of the given mouse-button-press event. - Function: event-modifiers EVENT This function returns a list of symbols, the names of the modifier keys which were down when the given mouse or keyboard event was produced. - Function: event-modifier-bits EVENT This function returns a number representing the modifier keys which were down when the given mouse or keyboard event was produced. - Function: event-function EVENT This function returns the callback function of the given timeout, misc-user, or eval event. - Function: event-object EVENT This function returns the callback function argument of the given timeout, misc-user, or eval event. - Function: event-process EVENT This function returns the process of the given process event. File: lispref.info, Node: Working With Events, Next: Converting Events, Prev: Accessing Other Event Info, Up: Events Working With Events ------------------- XEmacs provides primitives for creating, copying, and destroying event objects. Many functions that return events take an event object as an argument and fill in the fields of this event; or they make accept either an event object or `nil', creating the event object first in the latter case. - Function: allocate-event This function returns an empty event structure. WARNING: The event object returned may be a reused one; see the function `deallocate-event'. - Function: copy-event EVENT1 &optional EVENT2 This function makes a copy of the given event object. If a second argument is given, the first event is copied into the second and the second is returned. If the second argument is not supplied (or is `nil') then a new event will be made as with `allocate-event'. - Function: deallocate-event EVENT This function allows the given event structure to be reused. You *MUST NOT* use this event object after calling this function with it. You will lose. It is not necessary to call this function, as event objects are garbage-collected like all other objects; however, it may be more efficient to explicitly deallocate events when you are sure that that is safe. File: lispref.info, Node: Converting Events, Prev: Working With Events, Up: Events Converting Events ----------------- XEmacs provides some auxiliary functions for converting between events and other ways of representing keys. These are useful when working with ASCII strings and with keymaps. - Function: character-to-event CH &optional EVENT DEVICE This function converts a numeric ASCII value to an event structure, replete with modifier bits. CH is the character to convert, and EVENT is the event object to fill in. This function contains knowledge about what the codes "mean" - for example, the number 9 is converted to the character Tab, not the distinct character Control-I. Note that CH does not have to be a numeric value, but can be a symbol such as `clear' or a list such as `(control backspace)'. If `event' is not `nil', it is modified; otherwise, a new event object is created. In both cases, the event is returned. Optional third arg DEVICE is the device to store in the event; this also affects whether the high bit is interpreted as a meta key. A value of `nil' means use the selected device but always treat the high bit as meta. Beware that `character-to-event' and `event-to-character' are not strictly inverse functions, since events contain much more information than the ASCII character set can encode. - Function: event-to-character EVENT &optional ALLOW-EXTRA-MODIFIERS ALLOW-META ALLOW-NON-ASCII This function returns the closest ASCII approximation to EVENT. If the event isn't a keypress, this returns `nil'. If ALLOW-EXTRA-MODIFIERS is non-`nil', then this is lenient in its translation; it will ignore modifier keys other than control and meta, and will ignore the shift modifier on those characters which have no shifted ASCII equivalent (Control-Shift-A for example, will be mapped to the same ASCII code as Control-A). If ALLOW-META is non-`nil', then the Meta modifier will be represented by turning on the high bit of the byte returned; otherwise, `nil' will be returned for events containing the Meta modifier. If ALLOW-NON-ASCII is non-`nil', then characters which are present in the prevailing character set (*note variable `character-set-property': Keymaps.) will be returned as their code in that character set, instead of the return value being restricted to ASCII. Note that specifying both ALLOW-META and ALLOW-NON-ASCII is ambiguous, as both use the high bit; M-x and oslash will be indistinguishable. - Function: events-to-keys EVENTS &optional NO-MICE Given a vector of event objects, this function returns a vector of key descriptors, or a string (if they all fit in the ASCII range). Optional arg NO-MICE means that button events are not allowed. File: lispref.info, Node: Reading Input, Next: Waiting, Prev: Events, Up: Command Loop Reading Input ============= The editor command loop reads keyboard input using the function `next-event' and constructs key sequences out of the events using `dispatch-event'. Lisp programs can also use the function `read-key-sequence', which reads input a key sequence at a time. See also `momentary-string-display' in *Note Temporary Displays::, and `sit-for' in *Note Waiting::. *Note Terminal Input::, for functions and variables for controlling terminal input modes and debugging terminal input. For higher-level input facilities, see *Note Minibuffers::. * Menu: * Key Sequence Input:: How to read one key sequence. * Reading One Event:: How to read just one event. * Dispatching an Event:: What to do with an event once it has been read. * Quoted Character Input:: Asking the user to specify a character. * Peeking and Discarding:: How to reread or throw away input events. File: lispref.info, Node: Key Sequence Input, Next: Reading One Event, Up: Reading Input Key Sequence Input ------------------ Lisp programs can read input a key sequence at a time by calling `read-key-sequence'; for example, `describe-key' uses it to read the key to describe. - Function: read-key-sequence PROMPT This function reads a sequence of keystrokes or mouse clicks and returns it as a vector of events. It keeps reading events until it has accumulated a full key sequence; that is, enough to specify a non-prefix command using the currently active keymaps. The vector and the event objects it contains are freshly created, and will not be side-effected by subsequent calls to this function. The function `read-key-sequence' suppresses quitting: `C-g' typed while reading with this function works like any other character, and does not set `quit-flag'. *Note Quitting::. 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. If the user selects a menu item while we are prompting for a key sequence, the returned value will be a vector of a single menu-selection event (a misc-user event). An error will be signalled if you pass this value to `lookup-key' or a related function. 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 ---------- => [#<keypress-event control-X> #<keypress-event control-F>] 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. File: lispref.info, Node: Reading One Event, Next: Dispatching an Event, Prev: Key Sequence Input, Up: Reading Input Reading One Event ----------------- The lowest level functions for command input are those which read a single event. These functions often make a distinction between "command events", which are user actions (keystrokes and mouse actions), and other events, which serve as communication between XEmacs and the window system. - Function: next-event &optional EVENT PROMPT This function reads and returns the next available event from the window system or terminal driver, waiting if necessary until an event is available. Pass this object to `dispatch-event' to handle it. If an event object is supplied, it is filled in and returned; otherwise a new event object will be created. Events can come directly from the user, from a keyboard macro, or from `unread-command-events'. In most cases, the function `next-command-event' is more appropriate. - Function: next-command-event &optional EVENT This function returns the next available "user" event from the window system or terminal driver. Pass this object to `dispatch-event' to handle it. If an event object is supplied, it is filled in and returned, otherwise a new event object will be created. The event returned will be a keyboard, mouse press, or mouse release event. If there are non-command events available (mouse motion, sub-process output, etc) then these will be executed (with `dispatch-event') and discarded. This function is provided as a convenience; it is equivalent to the Lisp code (while (progn (next-event event) (not (or (key-press-event-p event) (button-press-event-p event) (button-release-event-p event) (menu-event-p event)))) (dispatch-event event)) Here is what happens if you call `next-command-event' and then press the right-arrow function key: (next-command-event) => #<keypress-event right> - Function: read-char This function reads and returns a character of command input. If a mouse click is detected, an error is signalled. The character typed is returned as an ASCII value. This function is retained for compatibility with Emacs 18, and is most likely the wrong thing for you to be using: consider using `next-command-event' instead. - Function: enqueue-eval-event FUNCTION OBJECT This function adds an eval event to the back of the queue. The eval event will be the next event read after all pending events. File: lispref.info, Node: Dispatching an Event, Next: Quoted Character Input, Prev: Reading One Event, Up: Reading Input Dispatching an Event -------------------- - Function: dispatch-event EVENT Given an event object returned by `next-event', this function executes it. This is the basic function that makes XEmacs respond to user input; it also deals with notifications from the window system (such as Expose events). File: lispref.info, Node: Quoted Character Input, Next: Peeking and Discarding, Prev: Dispatching an Event, Up: Reading Input Quoted Character Input ---------------------- You can use the function `read-quoted-char' to ask the user to specify a character, and allow the user to specify a control or meta character conveniently, either literally or as an octal character code. The command `quoted-insert' uses this function. - Function: read-quoted-char &optional PROMPT This function is like `read-char', except that if the first character read is an octal digit (0-7), it reads up to two more octal digits (but stopping if a non-octal digit is found) and returns the character represented by those digits in octal. Quitting is suppressed when the first character is read, so that the user can enter a `C-g'. *Note Quitting::. If PROMPT is supplied, it specifies a string for prompting the user. The prompt string is always displayed in the echo area, followed by a single `-'. In the following example, the user types in the octal number 177 (which is 127 in decimal). (read-quoted-char "What character") ---------- Echo Area ---------- What character-`177' ---------- Echo Area ---------- => 127 File: lispref.info, Node: Peeking and Discarding, Prev: Quoted Character Input, Up: Reading Input Miscellaneous Event Input Features ---------------------------------- This section describes how to "peek ahead" at events without using them up, how to check for pending input, and how to discard pending input. See also the variables `last-command-event' and `last-command-char' (*Note Command Loop Info::). - Variable: unread-command-events This variable holds a list of events waiting to be read as command input. The events are used in the order they appear in the list, and removed one by one as they are used. The variable is needed because in some cases a function reads a event and then decides not to use it. Storing the event in this variable causes it to be processed normally, by the command loop or by the functions to read command input. For example, the function that implements numeric prefix arguments reads any number of digits. When it finds a non-digit event, it must unread the event so that it can be read normally by the command loop. Likewise, incremental search uses this feature to unread events with no special meaning in a search, because these events should exit the search and then execute normally. - Variable: unread-command-event This variable holds a single event to be read as command input. This variable is mostly obsolete now that you can use `unread-command-events' instead; it exists only to support programs written for versions of XEmacs prior to 19.12. - Function: input-pending-p This function determines whether any command input is currently available to be read. It returns immediately, with value `t' if there is available input, `nil' otherwise. On rare occasions it may return `t' when no input is available. - Variable: last-input-event This variable is set to the last keyboard or mouse button event received. This variable is off limits: you may not set its value or modify the event that is its value, as it is destructively modified by `read-key-sequence'. If you want to keep a pointer to this value, you must use `copy-event'. Note that this variable is an alias for `last-input-char' in FSF Emacs. In the example below, a character is read (the character `1'). It becomes the value of `last-input-event', while `C-e' (from the `C-x C-e' command used to evaluate this expression) remains the value of `last-command-event'. (progn (print (next-command-event)) (print last-command-event) last-input-event) -| #<keypress-event 1> -| #<keypress-event control-E> => #<keypress-event 1> - Variable: last-input-char If the value of `last-input-event' is a keyboard event, then this is the nearest ASCII equivalent to it. Remember that there is *not* a 1:1 mapping between keyboard events and ASCII characters: the set of keyboard events is much larger, so writing code that examines this variable to determine what key has been typed is bad practice, unless you are certain that it will be one of a small set of characters. This function exists for compatibility with Emacs version 18. - Function: discard-input This function discards the contents of the terminal input buffer and cancels any keyboard macro that might be in the process of definition. It returns `nil'. In the following example, the user may type a number of characters right after starting the evaluation of the form. After the `sleep-for' finishes sleeping, `discard-input' discards any characters typed during the sleep. (progn (sleep-for 2) (discard-input)) => nil File: lispref.info, Node: Waiting, Next: Quitting, Prev: Reading Input, Up: Command Loop Waiting for Elapsed Time or Input ================================= The wait functions are designed to wait for a certain amount of time to pass or until there is input. For example, you may wish to pause in the middle of a computation to allow the user time to view the display. `sit-for' pauses and updates the screen, and returns immediately if input comes in, while `sleep-for' pauses without updating the screen. Note that in FSF Emacs, the commands `sit-for' and `sleep-for' take two arguments to specify the time (one integer and one float value), instead of a single argument that can be either an integer or a float. - Function: sit-for SECONDS &optional NODISP This function performs redisplay (provided there is no pending input from the user), then waits SECONDS seconds, or until input is available. The result is `t' if `sit-for' waited the full time with no input arriving (see `input-pending-p' in *Note Peeking and Discarding::). Otherwise, the value is `nil'. The argument SECONDS need not be an integer. If it is a floating point number, `sit-for' waits for a fractional number of seconds. Redisplay is normally preempted if input arrives, and does not happen at all if input is available before it starts. (You can force screen updating in such a case by using `force-redisplay'. *Note Refresh Screen::.) If there is no input pending, you can force an update with no delay by using `(sit-for 0)'. If NODISP is non-`nil', then `sit-for' does not redisplay, but it still returns as soon as input is available (or when the timeout elapses). The usual purpose of `sit-for' is to give the user time to read text that you display. - Function: sleep-for SECONDS This function simply pauses for SECONDS seconds without updating the display. This function pays no attention to available input. It returns `nil'. The argument SECONDS need not be an integer. If it is a floating point number, `sleep-for' waits for a fractional number of seconds. Use `sleep-for' when you wish to guarantee a delay. *Note Time of Day::, for functions to get the current time.