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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 <xml><body>
<div>
<p>zero is two: {[shw (is_two O)]}</p>
<p>one is two: {[shw (is_two (S O))]}</p>
<p>two is two: {[shw (is_two (S (S O)))]}</p>
</div>
<button onclick={fn _ => let
val m =
"zero is two: " ^ shw (is_two O) ^ "\n" ^
"one is two: " ^ shw (is_two (S O)) ^ "\n" ^
"two is two: " ^ shw (is_two (S (S O)))
in
alert m
end}>click me</button>
</body></xml>
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