really awful thue-morse generator in common lisp

tm.lisp

(defun tm-compute (loops)
  (let ((current 1) (ones 0) (complement 0))
    (dotimes (loop loops)
      (setf ones (- (expt 2 (- (length (format nil "0~B" current)) 0)) 1))
      (setf complement (- ones current))
      (setf current (parse-integer (format nil "~B~B" current complement) :radix 2)))
    (format t "0~B" current)))

; call with:
; (tm-compute number-of-loops-to-do)