type aliases and recursive modules

["Josh Berdine" <berdine@dcs.qmul.ac.uk>]

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Hi,

 

There's something I'm not understanding about recursive modules.  Consider
the following distilled example:

 

# 

module rec A : sig

  type t = It of ASet.t

  val compare : t -> t -> int

  val get : t -> ASet.t

end = struct

  type t = It of ASet.t

  let compare = compare

  let get = function It(x) -> x

end

 

and ASet : sig

  type t

  val get_its_elements : t -> A.t list

end = struct

  module C = Set.Make(A)

  type t = C.t

  let get_its_elements x = C.elements (A.get x)

end

;;

Characters 350-359:

    let get_its_elements x = C.elements (A.get x)

                                        ^^^^^^^^^

This expression has type ASet.t but is here used with type

  C.t = Set.Make(A).t

#

 

Why doesn't the typechecker know that ASet.t and C.t are the same type?
Anyone know a workaround?

 

This is with the 3.10.0 beta version, but seems to be the same back to 3.07.

 

Cheers,  Josh


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