CommonLisp / LeetCode "1614. max nesting depth of the parentheses"

  (defun max-nested-parentheses (s)
    (declare (optimize (speed 3) (safety 0))
             (type simple-string s))
    (loop with n fixnum = 0
          for ch across s
          when (member ch '(#\( #\)))
          do (incf n (if (eql #\( ch) 1 -1))
             maximizing n))