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with-open-stream Streams Dictionary clear-input
Function

listen

listen &optional input-stream ⇒ generalized-boolean

Arguments and Values

input-streaman input stream designator. The default is standard input.
generalized-booleana 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!

Affected By

*standard-input*

See Also

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

Backlinks

broadcast-stream, Input, Output, and Bidirectional Streams, read-char-no-hang, Stream Arguments to Standardized Functions, Streams Dictionary, Symbols in the COMMON-LISP Package