datatype cs52int = Pos of int list |
                   Zero |
                   Neg of int list;

fun isPositive (Pos _) = true
  | isPositive _       = false;

fun isNonzero Zero = false
  | isNonzero x    = true;

fun numDigits Zero    = 1
  | numDigits (Pos x) = length x
  | numDigits (Neg x) = length x;

fun numDigitsOther Zero          = 1
  | numDigitsOther (Pos [])      = 0 
  | numDigitsOther (Pos (x::xs)) = 1 + numDigitsOther (Pos xs)
  | numDigitsOther (Neg lst)     = numDigitsOther (Pos lst);