;; Shameless edit of ##sys#char->utf8-string

(define (char->utf8-length c)
  (let ([i (char->integer c)])
    (cond ((<= i #x7F) 1)
          ((<= i #x7FF) 2)
          ((<= i #xFFFF) 3)
          ((<= i #x1FFFFF) 4)
          (else
           (error "UTF-8 codepoint out of range:" i)))))