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[Caml-list] Multiparameter functors?
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Date: 2003-12-22 (23:44)
From: Julien Demouth <julien.demouth@f...>
Subject: Re: [Caml-list] Multiparameter functors?

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 ;)



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