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structure Nat =
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struct
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datatype nat = Suc of nat | Zero_nat;
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end; (*struct Nat*)
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structure Codegen =
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struct
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22386
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type 'a null = {null : 'a};
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fun null (A_:'a null) = #null A_;
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fun head B_ (x :: xs) = x
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| head B_ [] = null B_;
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fun null_option () = {null = NONE} : ('b option) null;
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val dummy : Nat.nat option =
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head (null_option ()) [SOME (Nat.Suc Nat.Zero_nat), NONE];
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end; (*struct Codegen*)
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