s.scm

(let loop ((plist the-plist))
  (when (not (null? plist))
    ;; Here you do something that might or might not result in
    ;; something. We do not know, "..." could be anything.
    (let ((key (car plist))
          (val (cadr plist)))
      ...)
    ;; But here, you ignore the result, and just loop over the list.
    (loop (cddr plist))))