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ANSI Common Lisp  21 Streams 21.2 Dictionary of Streams
- 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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