(use-modules (srfi srfi-39))


(define (check a b a-val b-val)
  (if (not (eqv? (a) a-val)) (error "failure -- a" (a) a-val))
  (if (not (eqv? (b) b-val)) (error "failure -- b" (b) b-val)))

(define a (make-parameter 3))
(define b (make-parameter 4))

(check a b 3 4)

(parameterize ((a 2) (b 1))
  (check a b 2 1)
  (parameterize ((b 8))
    (check a b 2 8)))

(check a b 3 4)

(define c (make-parameter 2 (lambda (x) (if (< x 10) x 10))))
(define d (make-parameter 15 (lambda (x) (if (< x 10) x 10))))

(check c d 2 10)

(parameterize ((a 0) (b 1) (c 98) (d 9))
  (check a b 0 1)
  (check c d 10 9)
  (parameterize ((c (a)) (d (b)))
    (check a b 0 1)
    (check c d 0 1)))