如何访问元组的随机成员？

val lis = (\"a\",\"b\",\"c\",\"d\")
val randNumber = Random.randRange (1,4) (Random.rand (0,1)) 
val randChar = #randNumber lis //this is where its failing

val lis = (\"a\",\"b\",\"c\",\"d\")
val ranChar = #2 lis;

#2

randNumber

    val randChar = case randNumber of
                      1 => #1 lis
                    | 2 => #2 lis
                    | 3 => #3 lis
                    | _ => #4 lis

lis

List

List.nth

List.nth(lis, randNumber-1)