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This section describes functions used to ask the user a yes-or-no
question. The function y-or-n-p can be answered with a single
character; it is useful for questions where an inadvertent wrong answer
will not have serious consequences. yes-or-no-p is suitable for
more momentous questions, since it requires three or four characters to
answer. Variations of these functions can be used to ask a yes-or-no
question using a dialog box, or optionally using one.
If either of these functions is called in a command that was invoked using the mouse, then it uses a dialog box or pop-up menu to ask the question. Otherwise, it uses keyboard input.
Strictly speaking, yes-or-no-p uses the minibuffer and
y-or-n-p does not; but it seems best to describe them together.
This function asks the user a question, expecting input in the echo
area. It returns t if the user types y, nil if the
user types n. This function also accepts SPC to mean yes
and DEL to mean no. It accepts C-] to mean “quit”, like
C-g, because the question might look like a minibuffer and for
that reason the user might try to use C-] to get out. The answer
is a single character, with no RET needed to terminate it. Upper
and lower case are equivalent.
“Asking the question” means printing prompt in the echo area, followed by the string ‘(y or n) ’. If the input is not one of the expected answers (y, n, SPC, DEL, or something that quits), the function responds ‘Please answer y or n.’, and repeats the request.
This function does not actually use the minibuffer, since it does not allow editing of the answer. It actually uses the echo area (see The Echo Area), which uses the same screen space as the minibuffer. The cursor moves to the echo area while the question is being asked.
The answers and their meanings, even ‘y’ and ‘n’, are not
hardwired. The keymap query-replace-map specifies them.
See Search and Replace.
In the following example, the user first types q, which is invalid. At the next prompt the user types y.
(y-or-n-p "Do you need a lift? ") ;; After evaluation of the preceding expression, ;; the following prompt appears in the echo area:
---------- Echo area ---------- Do you need a lift? (y or n) ---------- Echo area ----------
;; If the user then types q, the following appears:
---------- Echo area ---------- Please answer y or n. Do you need a lift? (y or n) ---------- Echo area ----------
;; When the user types a valid answer, ;; it is displayed after the question:
---------- Echo area ---------- Do you need a lift? (y or n) y ---------- Echo area ----------
We show successive lines of echo area messages, but only one actually appears on the screen at a time.
This function asks the user a question, expecting input in the
minibuffer. It returns t if the user enters ‘yes’,
nil if the user types ‘no’. The user must type RET to
finalize the response. Upper and lower case are equivalent.
yes-or-no-p starts by displaying prompt in the echo area,
followed by ‘(yes or no) ’. The user must type one of the
expected responses; otherwise, the function responds ‘Please answer
yes or no.’, waits about two seconds and repeats the request.
yes-or-no-p requires more work from the user than
y-or-n-p and is appropriate for more crucial decisions.
Here is an example:
(yes-or-no-p "Do you really want to remove everything? ") ;; After evaluation of the preceding expression, ;; the following prompt appears, ;; with an empty minibuffer:
---------- Buffer: minibuffer ---------- Do you really want to remove everything? (yes or no) ---------- Buffer: minibuffer ----------
If the user first types y RET, which is invalid because this function demands the entire word ‘yes’, it responds by displaying these prompts, with a brief pause between them:
---------- Buffer: minibuffer ---------- Please answer yes or no. Do you really want to remove everything? (yes or no) ---------- Buffer: minibuffer ----------
This function asks the user a “y or n” question with a popup dialog
box. It returns t if the answer is “yes”. prompt is the
string to display to ask the question.
The following functions ask a question either in the minibuffer or a
dialog box, depending on whether the last user event (which presumably
invoked this command) was a keyboard or mouse event. When SXEmacs is
running on a window system, the functions y-or-n-p and
yes-or-no-p are replaced with the following functions, so that
menu items bring up dialog boxes instead of minibuffer questions.
This function asks user a “y or n” question, using either a dialog box or the minibuffer, as appropriate.
This function asks user a “yes or no” question, using either a dialog box or the minibuffer, as appropriate.
Next: Multiple Queries, Previous: Completion, Up: Minibuffers [Contents][Index]