clear-input (ANSI and GNU Common Lisp Document)

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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