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(* Datatypes with a single constructor are normally represented as the value,
i.e. the contructor is an identity function. We optimise the case of
constructors of tuples so that B values are triples containing the
tag, a and b. We MUSTN'T do that for ref. *)
datatype 'a t = T of 'a
type q = {a: string, b: string};
datatype s = A | B of q t | C of int;
let
val x = B(T{a="O", b="K"})
val B(T{a,b}) = x
in
a^b
end;
datatype s = A | B of q ref | C of int;
let
val x = B(ref{a="WRO", b="NG"})
val B r = x
val _ = r := {a="O", b="K"}
val B(ref{a,b}) = x
in
if a^b = "OK" then () else raise Fail "Wrong"
end;
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