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21.2.35 clear-input [Function]

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