(define string->vector
  (case-lambda
    ((s) (string->vector s 0 (string-length s)))
    ((s start) (string->vector s start (string-length s)))
    ((s start end)
     (let ((len (- end start)))
       (do ((vec (make-vector len))
            (i 0 (+ i 1))
            (j start (+ j 1)))
           ((= i len) vec)
         (vector-set! vec i (string-ref s j)))))))