lookup-keyword

(defun lookup-keyword
  (keyword l)
  (declare (xargs :guard (keyword-value-listp l)))
  (cadr (assoc-keyword keyword l)))

(defun lookup-keyword-safe
  (keyword l)
  (let ((res (assoc-keyword keyword l)))
    (if (not res)
      (er hard?
        'lookup-keyword-safe
        "The keyword ~x0 is not present in the alist ~x1."
        keyword
        l)
      (cadr res))))