Do you know how or why that mistake happened?
And here’s some lisp code with parentheses you can match. The operator (or sometimes something else) goes immediately after (instead of before) its open parenthesis.
You can do color coding, arrows, or number (or letter) each open paren, then number the closed paren to match.
Ignore Discourse’s syntax highlighting which is wrong.
(defun ensure-generic-fn (message)
"Define an object-oriented dispatch function for a message,
unless it has already been defined as one."
(unless (generic-fn-p message)
(let ((fn #'(lambda (object &rest args)
(apply (get-method object message) args))))
(setf (symbol-function message) fn)
(setf (get message 'generic-fn) fn))))