Common Lisp HyperSpec のシンボルを眺めたり評価したりしています。今日は yes-or-no-p です。 y-or-n-p もほぼ同じ関数のようです。
---------------------------------------------------------------------------------------------------------------------------------------------------------- Function Y-OR-N-P, YES-OR-NO-P 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*. Exceptional Situations: None. 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. ---------------------------------------------------------------------------------------------------------------------------------------------------------- The following X3J13 cleanup issue, not part of the specification, applies to this section: * FORMAT-STRING-ARGUMENTS:SPECIFY ----------------------------------------------------------------------------------------------------------------------------------------------------------
ユーザーに何か尋ねるときに使う関数のようです。返り値は T または NIL 。第一引数に、質問内容をあらわすメッセージを文字列で与え、 FORMAT の書式を与えることもでき、その場合は第二引数以降に埋め込む値を並べる。
評価してみた結果はこちら。
(progn (print "How are you?") (if (yes-or-no-p) (print "Good.") (print "Bless you.")))
