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

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