y-or-n-p; yes-or-no-p - ANSI Common Lisp

Next: make-synonym-stream, Previous: finish-output; force-output; clear-output, Up: Streams

y-or-n-p, yes-or-no-p (Function)

Syntax:

— Function: y-or-n-p &optional control &rest arguments → generalized-boolean

— Function: yes-or-no-p &optional control &rest arguments → generalized-boolean

Arguments and Values:

control—a format control.

arguments—format arguments for control.

generalized-boolean—a generalized boolean.

Description:

These functions ask a question and parse a response from the user. They return true if the answer is affirmative, or false if the answer is negative.

y-or-n-p is for asking the user a question whose answer is either “yes” or “no.” It is intended that the reply require the user to answer a yes-or-no question with a single character. yes-or-no-p is also for asking the user a question whose answer is either “Yes” or “No.” It is intended that the reply require the user to take more action than just a single keystroke, such as typing the full word yes or no followed by a newline.

y-or-n-p types out a message (if supplied), reads an answer in some implementation-dependent manner (intended to be short and simple, such as reading a single character such as Y or N). yes-or-no-p types out a message (if supplied), attracts the user's attention (for example, by ringing the terminal's bell), and reads an answer in some implementation-dependent manner (intended to be multiple characters, such as YES or NO).

If format-control is supplied and not nil, then a fresh-line operation is performed; then a message is printed as if format-control and arguments were given to format. In any case, yes-or-no-p and y-or-n-p will provide a prompt such as “(Y or N)” or “(Yes or No)” if appropriate.

All input and output are performed using query I/O.

Examples:

 (y-or-n-p "(t or nil) given by")
▷ (t or nil) given by (Y or N) Y
→ true
 (yes-or-no-p "a ~S message" 'frightening)
▷ a FRIGHTENING message (Yes or No) no
→ false
 (y-or-n-p "Produce listing file?")
▷ Produce listing file?
▷ Please respond with Y or N. n
→ false

Side Effects:

Output to and input from query I/O will occur.

Affected By:

*query-io*.

Notes:

yes-or-no-p and yes-or-no-p do not add question marks to the end of the prompt string, so any desired question mark or other punctuation should be explicitly included in the text query.