+ (format nil "`~C'" char))
+ (t (format nil "<~(~:C~)>" char))))
+
+(defun %skip-until (scanner token-types
+ &key (keep-end (not (null (cdr token-types)))))
+ "This is the implementation of the `skip-until' parser."
+ (do ((consumedp nil t))
+ ((let ((type (token-type scanner))
+ (value (token-value scanner)))
+ (some (lambda (spec)
+ (multiple-value-bind (want-type want-value)
+ (cond ((listp spec) (values (car spec) (cadr spec)))
+ (t (values spec t)))
+ (and (eq want-type type)
+ (or (eq want-value t)
+ (equal want-value value)))))
+ token-types))
+ (unless keep-end (scanner-step scanner))
+ (values nil t (or keep-end consumedp)))
+ (when (scanner-at-eof-p scanner)
+ (return (values token-types nil consumedp)))
+ (scanner-step scanner)))
+
+(defun parse-error-recover (scanner parser recover
+ &key ignore-unconsumed force-progress)
+ "This is the implementation of the `error' parser."
+ (multiple-value-bind (result win consumedp) (funcall parser)
+ (cond ((or win
+ (and (not consumedp)
+ (or ignore-unconsumed
+ (scanner-at-eof-p scanner))))
+ ;; If we succeeded, or if we didn't consume any tokens and the
+ ;; caller's OK with that, then there's nothing for us to do here.
+ ;; On the other hand, if we failed, didn't consume any tokens, and
+ ;; we're at end-of-file, then there's not much hope of making
+ ;; onward progress, so in this case we propagate the failure
+ ;; rather than trying to recover. And we assume that the
+ ;; continuation will somehow arrange to report the problem, and
+ ;; avoid inundating the user with error reports.
+ (values result win consumedp))
+ (t
+ ;; Now we have to do some kind of sensible error recovery. The
+ ;; important thing to do here is to make sure that we make some
+ ;; progress. If we consumed any tokens then we're fine, and we'll
+ ;; just try the provided recovery strategy. Otherwise, if we're
+ ;; not at EOF, then we can ensure progress by discarding the
+ ;; current token. Finally, if we are at EOF then our best bet is
+ ;; simply to propagate the current failure back to the caller, but
+ ;; we handled that case above.
+ (syntax-error scanner result)
+ (when (and force-progress (not consumedp)) (scanner-step scanner))
+ (funcall recover)))))