Aha! That's more like what I was going for, Martin.
I didn't realize you could equate types in a chain like that, permitting
the definition of structure but also equality to another existing type.
That's good stuff.
This list, and OCaml, often amaze me... solutions keep getting better. :)
On Wed, Nov 2, 2011 at 6:41 PM, Martin Jambon <martin.jam...@ens-lyon.org>wrote:
> On 11/02/2011 12:41 PM, Anthony Tavener wrote:
> > I've been struggling with this occasionally...
> >
> > I'm using nested modules to "open" access to select features of a
> > module. My problem is I can't find a way to *expose* types in the parent
> > module through such nested modules.
> >
> > A simplified example of what I'm looking at:
> >
> > module Vec = struct
> >
> > type t = { x: int; y: int }
> > let make x y = {x;y}
> > let add a b = {x=a.x+b.x; y=a.y+b.y}
> >
> > module Type =
> > (* something which has type t = Vec.t,
> > * with exposed structure when "open"ed.
> > * Also note that Vec is not really an
> > * explicit module like this; instead it
> > * is implemented in vec.ml <http://vec.ml> *)
> > end
> >
> > Example usage...
> >
> > let n = Vec.make 2 5
> > open Vec.Type
> > let m = {x=1;y=2}
> > Vec.add m n
>
> I hope I understand the problem correctly.
>
> In order for that code to work, you can do this:
>
> module Vec = struct
>
> type t = { x: int; y: int }
> let make x y = {x;y}
> let add a b = {x=a.x+b.x; y=a.y+b.y}
>
> module Type = struct
> type t' = t = { x: int; y: int }
> type t = t' = { x: int; y: int }
> (* something which has type t = Vec.t,
> * with exposed structure when "open"ed.
> * Also note that Vec is not really an
> * explicit module like this; instead it
> * is implemented in vec.ml <http://vec.ml> *)
> end
> end
>
>
> Or more simply:
>
>
> module Vec = struct
>
> module Type = struct
> type t = { x: int; y: int }
> (* something which has type t = Vec.t,
> * with exposed structure when "open"ed.
> * Also note that Vec is not really an
> * explicit module like this; instead it
> * is implemented in vec.ml <http://vec.ml> *)
> end
>
> type t = Type.t = { x: int; y: int }
> let make x y = {x;y}
> let add a b = {x=a.x+b.x; y=a.y+b.y}
>
> end
>
>
> Now you can open either Vec or Vec.Type and have direct access to the
> record fields.
>
>
> Martin
>
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