a question about recursiv type defintions and functors like Set.Make?
 Phillip Heidegger
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Date:   (:) 
From:  Phillip Heidegger <heidegger@i...> 
Subject:  a question about recursiv type defintions and functors like Set.Make? 
Hi, I have a question about using the set functor. I need a type like: CODE1: type a = BaseCase of string  BSet of b set  ASet of a set and b = BaseCaseB of string  ASetB of a set In my first implementation I used instead of sets lists and write some functions to manipulate the values of type a and b. But now I need a faster representation for the sets, and I try to use the module "Set". But I didn't find a way using it because of the recursion in the type definition. I would like to write something like: CODE2: type a = BaseCase of string  BSet of BSet.t  ASet of ASet.t and b = BaseCaseB of string  ASetB of ASet.t and module ASet = Set.Make(struct type a let compare x y = ...end) and module BSet = Set.Make(struct type b let compare x y = ...end) (of cause this is not valid OCaml Code, but I hope it helps to understand, what I would like to do). This code did not work because I used the type ASet.t in the definition of a, and the type a in the functor call of ASet. Because modules are not recursive in OCaml, I'm not able to write code like this I think. Now my next approach was not to use the Set module, but change the code of this module, so I get a module with polymorph signature: CODE3: module Set : sig type 'a t val empty : 'a t val is_empty : 'a t > bool val mem : ('a > 'a > int) > 'a > 'a t > bool .... (* nearly all functions need a method compare like mem *) end I can write my type as I desired in CODE1, but I have to pass to all functions, every time I used the set, the compare Function as a parameter. For example: if (mem cmpTypeA element aSet) then ...... Is there a better way to implement this set Module? Is there a way to use the Set functor code? Is there a way to get recursiv moduls in OCaml? How should I solve my problem, if I have recursive modules. If it's possible to solve my problem without using recursive modules, what should I do? greetings, Phillip