read-char-no-hang &optional input-stream eof-error-p
eof-value recursive-p ⇒ char
| input-stream | an input stream designator. The default is standard input. |
| eof-error-p | a generalized boolean. The default is true. |
| eof-value | an object. The default is nil. |
| recursive-p | a generalized boolean. The default is false. |
| char | a character or nil or the eof-value. |
read-char-no-hang returns a character from input-stream if such a character is available. If no character is available, read-char-no-hang returns nil.
If recursive-p is true, this call is expected to be embedded in a higher-level call to read or a similar function used by the Lisp reader.
If an end of file_2 occurs and eof-error-p is false, eof-value is returned.
;; This code assumes an implementation in which a newline is not
;; required to terminate input from the console.
(defun test-it ()
(unread-char (read-char))
(list (read-char-no-hang)
(read-char-no-hang)
(read-char-no-hang)))
⇒ TEST-IT
;; Implementation A, where a Newline is not required to terminate
;; interactive input on the console.
(test-it)
|> |>>a<<|
⇒ (#\a NIL NIL)
;; Implementation B, where a Newline is required to terminate
;; interactive input on the console, and where that Newline remains
;; on the input stream.
(test-it)
|> |>>a[<–~]<<|
⇒ (#\a #\Newline NIL)
*standard-input*, *terminal-io*.
If an end of file_2 occurs when eof-error-p is true, an error of type end-of-file is signaled .
read-char-no-hang is exactly like read-char, except that if it would be necessary to wait in order to get a character (as from a keyboard), nil is immediately returned without waiting.