Welcome to the CHICKEN Scheme pasting service

(define (digits->number lst base)
  (if (null? lst)
      0
      (let loop ((ret (car lst))
                 (lst (cdr lst))
                 (coeff base))
        (if (null? lst)
            ret
            (loop (+ ret (* (car lst) coeff))
                  (cdr lst)
                  (* coeff base))))))