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  ANSI Common Lisp   21 Streams   21.2 Dictionary of Streams

21.2.35 clear-input Function

Syntax:
clear-input &optional input-stream    nil

Arguments and Values:
input-stream - an input stream designator. The default is standard input.

Description:
Clears any available input from input-stream.

If clear-input does not make sense for input-stream, then clear-input does nothing.

Examples:
;; The exact I/O behavior of this example might vary from implementation
;; to implementation depending on the kind of interactive buffering that
;; occurs.  (The call to SLEEP here is intended to help even out the 
;; differences in implementations which do not do line-at-a-time buffering.)

(defun read-sleepily (&optional (clear-p nil) (zzz 0))
  (list (progn (print '>) (read))
        ;; Note that input typed within the first ZZZ seconds 
        ;; will be discarded.
        (progn (print '>) 
               (if zzz (sleep zzz))
               (print '>>)
               (if clear-p (clear-input))
               (read))))

(read-sleepily)
> 10
>
>> 20
 (10 20)

(read-sleepily t)
> 10
>
>> 20
 (10 20)

(read-sleepily t 10)
> 10
> 20  ; Some implementations won't echo typeahead here.
>> 30
 (10 30)

Side Effects:
The input-stream is modified.

Affected By:
*standard-input*

Exceptional Situations:
Should signal an error of type type-error if input-stream is not a stream designator.

See Also:
clear-output

Allegro CL Implementation Details:
None.

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