Playing with the Fisher-Yates shuffle and named lets. Comments/corrections welcome.

gistfile1.scm

(define (vector-swap! v idx1 idx2)
  (let ((temp (vector-ref v idx1)))
    (cond ((= idx1 idx2) v)
	  (else (vector-set! v idx1 (vector-ref v idx2))
		(vector-set! v idx2 temp)
		v))))

(define (vector-shuffle! vec)
  (let vec-shuf-helper ([v vec]
			[n (vector-length vec)])
    (if (<= n 1) v
	(vec-shuf-helper
	 (vector-swap! v (- n 1) (random n))
	 (- n 1)))))