clear-input (Function)

Syntax:

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