Python's range object in Scheme

range-obj.ss

#lang racket

(define range
  (case-lambda
    ((stop) (range 0 stop 1))
    ((start stop) (range start stop 1))
    ((start stop step) (list 'range start stop step))))

(define range?
  (lambda (obj)
    (eq? (car obj) 'range)))

(define range-start
  (lambda (obj)
    (car (cdr obj))))

(define range-stop
  (lambda (obj)
    (car (cdr (cdr obj)))))

(define range-step
  (lambda (obj)
    (car (cdr (cdr (cdr obj))))))

(define range-len
  (lambda (obj)
    (max 0 (ceiling (/ (- (range-stop obj) (range-start obj)) (range-step obj))))))

(define range-getitem
  (lambda (obj index)
    (if (not (< -1 index (range-len obj)))
        null
        (+ (range-start obj) (* index (range-step obj))))))))

(define range-iter
  (lambda (obj)
    (let ((index 0))
      (lambda ()
        (set! index (+ index 1))
        (range-getitem obj (- index 1))))))