ToC DocOverview CGDoc RelNotes Index PermutedIndex
Allegro CL
Home Previous Up Next Table of Contents Index
  ANSI Common Lisp   21 Streams   21.2 Dictionary of Streams

21.2.37 y-or-n-p, yes-or-no-p Function

Syntax:
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.

Allegro CL Implementation Details:
None.

Home Previous Up Next Table of Contents Index
© Franz Inc. 1998-2017 - File last updated 01-11-2017