zaltoprofen

(define (range start . args)
  (let-optionals* args ((stop #f) (step 1))
                  (define (rangei start stop ls)
                    (if (or (and (> step 0) (>= start stop)) (and (< step 0) (<= start stop)))
                      ls (rangei (+ start step) stop (cons start ls))))
                  (cond ((= step 0) (error "Step cannot take 0"))
                        ((not (integer? start)) (error "Integer required for 1st argument, but got:" start))
                        ((and stop (not (integer? stop))) (error "Integer required for 2nd argument, but got:" stop))
                        ((not (integer? step)) (error "Integer required for 3rd argument, but got:" step))
                        ((not stop) (reverse (rangei 0 start '())))