On Sat, Nov 03, 2007 at 11:20:16PM +0100, Michaël Le Barbier wrote:
> In some piece of code, I use functors combined with include as a kind
> of macro facility. In this scheme, it can happen that an identifier is
> exported multiple times from various include directives, this ``name
> collision'' is an error, and I am looking for ways to avoid it
> whithout much annoyance. (OK, this is very vague, details and example
> are coming.)
[...]

I'm not sure if it could be of some help, but here is another scheme
wherein the functor <name>Type.Make does not include its argument PROTO,
so that there is no namespace conflict with type t.
However the PROTO structure can no longer be used anonymously:

    include OrderedType.Make(struct type t let compare : t -> t -> int = Pervasives.compare end)

Gives the error message:

    This functor has type
    functor (PROTO : OrderedType.PROTO) ->
      sig val ge : PROTO.t -> PROTO.t -> bool end
    The parameter cannot be eliminated in the result type.
     Please bind the argument to a module identifier

The module identifier <name>Type_PROTO should be ok.

module OrderedType =
  struct
    module type PROTO =
      sig type t val compare : t -> t -> int end
    module Make
      (PROTO: PROTO) =
      struct let ge t t' = PROTO.compare t t' >= 0 end
  end
module FunnyType =
  struct
    module type PROTO =
      sig type t val compare : t -> t -> int end
    module Make
      (PROTO: PROTO) =
      struct let funny_ge t t' = PROTO.compare t t' >= 0 end
  end
module OrderedType_PROTO =
  struct type t let compare : t -> t -> int = Pervasives.compare end
module FunnyType_PROTO =
  struct type t let compare : t -> t -> int = Pervasives.compare end
include OrderedType.Make(OrderedType_PROTO)
include FunnyType.Make(FunnyType_PROTO)

Which gives:

module OrderedType :
  sig
    module type PROTO = sig type t val compare : t -> t -> int end
    module Make :
      functor (PROTO: PROTO) ->
      sig val ge : PROTO.t -> PROTO.t -> bool end
  end
module FunnyType :
  sig
    module type PROTO = sig type t val compare : t -> t -> int end
    module Make :
      functor (PROTO: PROTO) ->
      sig val funny_ge : PROTO.t -> PROTO.t -> bool end
  end
module OrderedType_PROTO : sig type t val compare : t -> t -> int end
module FunnyType_PROTO   : sig type t val compare : t -> t -> int end
val ge       : OrderedType_PROTO.t -> OrderedType_PROTO.t -> bool
val funny_ge : FunnyType_PROTO.t -> FunnyType_PROTO.t -> bool

HTH,
  Julien.