Syntax:
listen &optional input-stream => generalized-boolean
Arguments and Values:
input-stream---an input stream designator. The default is standard input.
generalized-boolean---a generalized boolean.
Description:
Returns true if there is a character immediately available from input-stream; otherwise, returns false. On a non-interactive input-stream, listen returns true except when at end of file[1]. If an end of file is encountered, listen returns false. listen is intended to be used when input-stream obtains characters from an interactive device such as a keyboard.
Examples:
(progn (unread-char (read-char)) (list (listen) (read-char))) >> 1 => (T #\1) (progn (clear-input) (listen)) => NIL ;Unless you're a very fast typist!
Side Effects: None.
Affected By:
Exceptional Situations: None.
See Also:
interactive-stream-p, read-char-no-hang
Notes: None.
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