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#### 21.2.37 y-or-n-p, yes-or-no-p [Function]

`y-or-n-p` &optional control &rest arguments ⇒ generalized-boolean

`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*.

#### See Also::

format

#### 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.

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