functor troubles

functor troubles

[Sam Steingold]

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It appears that module functor arguments are needlessly duplicated:

============================================
module A1 = struct
~  module F (M: sig end) = struct
~    type t = T
~  end
~  module I = struct end
~  module M = F (I)
end

module A2 = A1

let f : A1.M.t -> A2.M.t = fun x -> x
============================================

This expression has type A1.M.t = A1.F(A1.I).t but is here used with
type A2.M.t = A1.F(A2.I).t

when I replace "module M = F (I)" with "module M = F (struct end)" it works.

Note that the whole file invokes the functor F precisely once, so it is
not clear why type A2.M.t is defined in terms of F and not as identical
to A1.M.t.
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Re: [Caml-list] functor troubles

[Keiko Nakata]

Hello,

the following thread may be useful to you

http://caml.inria.fr/pub/ml-archives/caml-list/2007/03/80072743d454a8cdc79cb67c110586b0.en.html

With best regards,
Keiko


> It appears that module functor arguments are needlessly duplicated:
> 
> ============================================
> module A1 = struct
> ~  module F (M: sig end) = struct
> ~    type t = T
> ~  end
> ~  module I = struct end
> ~  module M = F (I)
> end
> 
> module A2 = A1
> 
> let f : A1.M.t -> A2.M.t = fun x -> x
> ============================================
> 
> This expression has type A1.M.t = A1.F(A1.I).t but is here used with
> type A2.M.t = A1.F(A2.I).t
> 
> when I replace "module M = F (I)" with "module M = F (struct end)" it works.
> 
> Note that the whole file invokes the functor F precisely once, so it is
> not clear why type A2.M.t is defined in terms of F and not as identical
> to A1.M.t.