The K language's ! operator in Scheme, or, Polymorphism gone wild

bang.scm

(import (srfi 1))

;; The K language's polymorphic ! operator
(define bang
  (case-lambda
    ((x)
     (iota x))
    ((x y)
     (cond
       ((exact-integer? y)
        (modulo x y))
       ((list? y)
        (list-rotate x y))))))

(define (list-rotate count list)
  (if (negative? count)
    (list-rotate (+ (length list) count) list)
    (append (drop list count) (take list count))))

;;; Scheme version of K expression 2!!7!4 from Wikipediaå
;;; K operators are right-associative
(bang 2 (bang (bang 7 4)))
;;; => (2 0 1)