listen
&optional input-stream ⇒ generalized-boolean
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 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.
(progn (unread-char (read-char)) (list (listen) (read-char)))|>
|>>1
<<| ⇒ (T #\1) (progn (clear-input) (listen)) ⇒ NIL ;Unless you're a very fast typist!
*standard-input*
interactive-stream-p [Function] , read-char-no-hang [Function]