#lang scheme/base

(provide (all-defined-out))

(define (range lower upper) (list lower upper))
(define (range-lower range) (list-ref range 0))
(define (range-upper range) (list-ref range 1))
(define (range-singular? range) (eq? (range-upper range) (range-lower range)))
(define (range-size range) (- (range-upper range) (range-lower range)))
(define (range-unbounded? range) (eq? (range-upper range) 'unbounded))

(define (range-in-range? range n)
  (and (>= n (range-lower range))
    (or (eq? (range-upper range) 'unbounded)
      (<= n (range-upper range)))))

(define (random-range range)
  (cond 
   ((range-singular? range) (range-lower range))
   ((range-unbounded? range) (+ (range-lower range) (random 4)))
   (else
    (+ (random (range-size range)) 
       (range-lower range)))))