[Alice-users] Functors that return environments with Functors

[Chris Rathman]

Was trying to do some stuff with Functors related to bundling operations
around state.  Can't seem to do what I want to do but since it's still an
idea that's not firm, I thought I'd simplify the source of the problem.  The
three examples use a module that sent to or returned from various functors
in the examples:

   signature T =
      sig
         type t
         val s : t list
      end

Nothing too involved.  Just want to see that I can pass a type as well as a
value.  Alice ML does allow me to return a functor via a functor along the
lines of:

   (* This compiles fine *)
   functor Dummy0 () : T =
      struct
         type t = int
         val s = nil
      end

   functor F0 (structure AType : T) =
      struct
         type t = AType.t
         val x = AType.s
         functor Fx () = Dummy0()
      end

Having a taste of this feature, I thought I'd go about the next logical step
and start passing around a module within the returned functor.  I'm not sure
why the compiler is complaining here?  All I'm trying to do is directly
passing the same module I got passed within the parent functor.

   (* This gives me an error:
         module expression does not match functor parameter
         signature:
            structure BType
         is missing 
    *)
   functor Dummy1 (structure BType : T) : T =
      struct
         type t = BType.t
         val s = BType.s
      end

   functor F1 (structure CType : T) =
      struct
         type t = CType.t
         val x = CType.s
         functor Fy () = Dummy1(CType)
      end

Well, having come to a dead end on passing around modules, I stripped down
to the bone the feature that I was really want to get to - self referring
functors.  But it seems that Functors can't be recursive called (if that's
the proper term for the effect that I'm trying to do here.

   (* This gives me an error:
          unknown structure or functor `F2'
    *)
   functor F2 () =
      struct
         type t = int
         val x = 1234::nil
         (* functor Fz () = F2() *)
      end

So what I really wanted to do was have a Functor that is passed a module as
in the second example, and have it return another functor that modifies that
environment as a module parameter to itself.  Kind of a Declarative Functor
if you will.

So, am I just trying to abuse the notion of Functors?  Or is there a way
around these two errors?

Thanks
Chris Rathman