Welcome to the CHICKEN Scheme pasting service

(define (u8vector->hex u8vector)
  (apply string-append
	 (reverse
	   (fold
	     (lambda (v s)
	       (let ((lo (bitwise-and v 15))
		     (hi (arithmetic-shift v -4)))
		 (cons* (number->string hi 16)
			(number->string lo 16)
			s)))
	     '()
	     (u8vector->list u8vector)))))