random (one-parameter)

;;; (random n) -> (all-of integer? (cut (<= 0 <>)) (cut (< <> n)))
;;;   n : positive-integer?
;;; Compute an unpredictable number between 0 (inclusive) and `n` (exclusive).

> (random 1)
0
> (random 1)
0
> (random 2)
1
> (random 2)
1
> (random 2)
0
> (random 2)
0
> (random 1000)
758
> (random 1000)
522
> (random 0)
. . random: contract violation
  expected: (or/c (integer-in 1 4294967087) pseudo-random-generator?)
  given: 0

(define random-n
  (lambda (n)
    (inexact->exact (floor (* n (random))))))