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| ANSI Common Lisp 21 Streams 21.2 Dictionary of Streams
21.2.34 listen | Function
  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 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. 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!
Affected By: *standard-input* See Also: interactive-stream-p, read-char-no-hang Allegro CL Implementation Details: None.

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