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Function READ-CHAR-NO-HANG

Syntax

  • read-char-no-hang &optional input-stream eof-error-p eof-value recursive-pchar

Arguments and Values

Description

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 occurs and eof-error-p is false, eof-value is returned.

Examples

(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)

Affected By

Exceptional Situations

If an end of file occurs when eof-error-p is true, an error of type end-of-file is signaled .

See Also

Notes

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.

\issue{ARGUMENTS-UNDERSPECIFIED:SPECIFY}