yes-or-no-p &optional control &rest arguments    generalized-boolean

arguments - format arguments for control.

generalized-boolean - a generalized boolean.

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.

 (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