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[Caml-list] Module equivalence across definitions
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Date: -- (:)
From: Lauri Alanko <la@i...>
Subject: [Caml-list] Module equivalence across definitions
[Pardon for possible duplicates]

Hello. Given:


module type T = sig
  type t
end

module A : T = struct
  type t = A
end

module B(X:T) = struct
  type t = B
  let v = B
end

module type CT = sig
  val a : B(A).t
end

module C : CT = struct
  module Aalias = A
  module BA = B(Aalias)
  let a = BA.v
end


I get an error:


Signature mismatch:
Modules do not match:
  sig
    module Aalias : sig type t = A.t end
    module BA : sig type t = B(Aalias).t = B val v : t end
    val a : BA.t
  end
is not included in
  CT
Values do not match: val a : BA.t is not included in val a : B(A).t


But changing "module BA = B(Aalias)" to "module BA = B(A)" makes everything
work.

What gives? I'm used to seeing structural equivalence being used everywhere
in O'Caml's type system, but here simply renaming a module seems to give it
a distinct new identity. Is this a bug or a feature?


Lauri Alanko
la@iki.fi
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