The code with optimization declaration may make SBCL to note some *unable to optimize* message.

parse-params.lisp

(defun parse-params (s)
  (labels ((aux (acc s)
             (declare (optimize (speed 3)))
             (let ((i1 (position #\= s))
                   (i2 (position #\& s)))
               (cond (i1 (aux (cons (cons (intern (string-upcase (subseq s 0 i1)))
                                          (decode-param (subseq s (1+ i1) i2)))
                                    acc)
                              (and i2 (subseq s (1+ i2)))))
                     ((equal s "") nil)
                     (t acc)))))
    (nreverse (aux '() s))))