[Caml-list] Multiparameter functors?

[Caml-list] Multiparameter functors?

[Brian Hurt]

Is it possible to do multi-parameter functors?  What I want to be able to 
so is something like:

module Make(Key: Map.OrderedType, Pri: Map.OrderedType) = struct
	type key = Key.t;;
	type pri = Pri.t;;
	...
end;;

Am I being stupid and just missing something obvious, or is there some 
subtle reason why I shouldn't be doing this?


-- 
"Usenet is like a herd of performing elephants with diarrhea -- massive,
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                                - Gene Spafford 
Brian

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Re: [Caml-list] Multiparameter functors?

[Julien Signoles]

> Is it possible to do multi-parameter functors?  What I want to be able to
> so is something like:
>
> module Make(Key: Map.OrderedType, Pri: Map.OrderedType) = struct
> 	type key = Key.t;;
> 	type pri = Pri.t;;
> 	...
> end;;

module Make(Key: Map.OrderedType)(Pri: Map.OrderedType) = struct
  type key = Key.t
  type pri = Pri.t
  (* ... *)
end

Julien Signoles
-- 
mailto:Julien.Signoles@lri.fr ; http://www.lri.fr/~signoles
"In theory, practice and theory are the same,
but in practice they are different" (Larry McVoy)

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Re: [Caml-list] Multiparameter functors?

[Brian Hurt]

Thanks everyone for your answers.

-- 
"Usenet is like a herd of performing elephants with diarrhea -- massive,
difficult to redirect, awe-inspiring, entertaining, and a source of
mind-boggling amounts of excrement when you least expect it."
                                - Gene Spafford 
Brian

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Re: [Caml-list] Multiparameter functors?

[Julien Demouth]

Hi,

Brian Hurt wrote:
> Is it possible to do multi-parameter functors?  What I want to be able to 
> so is something like:
> 
> module Make(Key: Map.OrderedType, Pri: Map.OrderedType) = struct
> 	type key = Key.t;;
> 	type pri = Pri.t;;
> 	...
> end;;

Of course it's possible but you mustn't use the comma. A functor is just 
a function. The only difference is that it deals with structure whereas 
"normal" functions deal with values. Consider the following example:

module type M = sig type t end

module type N = sig type t end

module type R = sig type u and v end

module Make (U:M) (V:N) : R with type u = U.t and type v = V.t

> Am I being stupid and just missing something obvious, or is there some 
> subtle reason why I shouldn't be doing this?

Every question is good to be asked ;)

Regards,

Julien


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Re: [Caml-list] Multiparameter functors?

[Matt Gushee]

On Sun, Dec 21, 2003 at 07:30:27PM -0500, Brian Hurt wrote:
> 
> Is it possible to do multi-parameter functors?  What I want to be able to 
> so is something like:
> 
> module Make(Key: Map.OrderedType, Pri: Map.OrderedType) = struct
> 	type key = Key.t;;
> 	type pri = Pri.t;;
> 	...
> end;;
> 
> Am I being stupid and just missing something obvious,

Is there anything obvious about functors? ;-)

I've found the following syntax to work:

  module Make =
    functor (Key:Map.OrderedType) -> functor (Pri:Map.OrderedType) ->
      struct
        ....
      end;;

... though I'm not qualified to comment on the merits of doing or not
doing this.

-- 
Matt Gushee                 When a nation follows the Way,
Englewood, Colorado, USA    Horses bear manure through
mgushee@havenrock.com           its fields;
http://www.havenrock.com/   When a nation ignores the Way,
                            Horses bear soldiers through
                                its streets.
                                
                            --Lao Tzu (Peter Merel, trans.)

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Re: [Caml-list] Multiparameter functors?

[David Brown]

On Mon, Dec 22, 2003 at 04:04:15PM -0700, Matt Gushee wrote:

> Is there anything obvious about functors? ;-)
> 
> I've found the following syntax to work:
> 
>   module Make =
>     functor (Key:Map.OrderedType) -> functor (Pri:Map.OrderedType) ->
>       struct
>         ....
>       end;;

This is very similar to currying of functions, except that Ocaml doesn't
give you nice convenient syntax for defining curried functors.  The
application is similar to currying, though.

  module Mine = Make (Keytype) (Pritype)

Dave.

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Re: [Caml-list] Multiparameter functors?

[David Brown]

> On Mon, Dec 22, 2003 at 04:04:15PM -0700, Matt Gushee wrote:
>
> > Is there anything obvious about functors? ;-)
> > 
> > I've found the following syntax to work:
> > 
> >   module Make =
> >     functor (Key:Map.OrderedType) -> functor (Pri:Map.OrderedType) ->
> >       struct
> >         ....
> >       end;;
> 
> This is very similar to currying of functions, except that Ocaml doesn't
> give you nice convenient syntax for defining curried functors.  The
> application is similar to currying, though.
> 
>   module Mine = Make (Keytype) (Pritype)

And, I'm not even right.  Module definitions can also be curried:

  module Make (Key : Map.OrderedType) (Pri : Map.OrderedType) =
    struct
      ...
    end

Dave

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