#### 21.2.34 listen [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.

#### 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 [Function] , read-char-no-hang [Function]