This seems to be a compiler bug, but let me know if I've missed something. The behavior I see is that Make_ok1 and Make_ok2 compile fine, but the very similar functor Make_bad does not. I get this compile error:

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Error: Signature mismatch:

Modules do not match:

sig

module C : sig module T : sig end type t = Make(T).t end

module T = C.T

type t = Make(T).t

end

is not included in

sig type t module C : sig type t = t end end

In module C:

Modules do not match:

sig module T : sig end type t = Make(T).t end

is not included in

sig type t = C.t end

In module C:

Type declarations do not match:

type t = Make(T).t

is not included in

type t = t

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And here is the code:

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module type S = sig type t end

module Make (M : sig end) : S = struct type t end

module Make_ok1 (M : sig end) : sig

type t

module A : S with type t = t

end = struct

module A = struct

include Make (struct end)

end

include A

end

module Make_ok2 (M : sig end) : sig

type t

module B : S with type t = t

end = struct

module T = struct end

module B = struct

include Make (T)

end

include B

end

module Make_bad (M : sig end) : sig

type t

module C : S with type t = t

end = struct

module C = struct

module T = struct end

include Make (T)

end

include C

end

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Carl Eastlund