structure ROOT =
struct
structure Nat =
struct
datatype nat = Zero_nat | Suc of nat;
end; (*struct Nat*)
structure Codegen =
struct
type 'a null = {Codegen__null : 'a};
fun null (A_:'a null) = #Codegen__null A_;
fun head A_ (y :: xs) = y
| head A_ [] = null A_;
val null_option : 'a option = NONE;
fun null_optiona () = {Codegen__null = null_option} : ('b option) null;
val dummy : Nat.nat option =
head (null_optiona ()) [SOME (Nat.Suc Nat.Zero_nat), NONE];
end; (*struct Codegen*)
end; (*struct ROOT*)