Next: , Previous: with-open-stream, Up: Streams

listen (Function)

— Function: 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.


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 file1. 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.

 (progn (unread-char (read-char)) (list (listen) (read-char)))
▷ 1
 (T #\1)
 (progn (clear-input) (listen))
 NIL ;Unless you're a very fast typist!
Affected By:


See Also:

interactive-stream-p, read-char-no-hang