fun f1 s =   case s of       SOME (a, b) => List.length a + b     | NONE => 0

fun f2 s =   case s of       SOME (a, b) => a + (List.foldl op+ 0 b)     | NONE => 1

fun f3 s =   case s of       SOME (a, b) => SOME (a*b)     | NONE => NONE