datatype t = A | B val swap = fn x : t => case x of A => B | B => A datatype u = C of t | D val out = fn x : u => case x of C y => y | D => A datatype nat = O | S of nat val is_two = fn x : nat => case x of S (S O) => A | _ => B val shw = fn x : t => case x of A => "A" | B => "B" fun main (): transaction page = return

zero is two: {[shw (is_two O)]}

one is two: {[shw (is_two (S O))]}

two is two: {[shw (is_two (S (S O)))]}