Re: [Caml-list] any types in signatures of functor arguments

[Brian Hurt <bhurt@spnz.org>]

On Mon, 24 Oct 2005, Keiko Nakata wrote:

> Hello.
>
> Why I cannot have *any types* in signatures of functor arguments?
> Concretely, the following F is not typable.
>
> module F(X:sig type t = [`A of _ ] val f : t -> int end) =
>  struct
>    let f = function `A x as a -> X.f a | `B -> 0
>  end

I think the problem is that `A holds something, but you're not giving 
Ocaml any idea of what.  For example, the following compiles:

module F(X:sig type 'a t = [`A of 'a ] val f : 'a t -> int end) =
   struct
     let f = function `A x as a -> X.f a | `B -> 0
   end

Hope this helps.

Brian