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Problem with module inclusion
• Fabrice Marchant
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 Date: 2008-06-04 (14:24) From: Fabrice Marchant Subject: Problem with module inclusion
```  Hi senior list !

Another question about learning OCaml : apologize. It lands here unchanged from Beginners list :

Here is a counter functor : *)

module Counters ( X : Map.OrderedType ) :
sig
module XMap :
sig
type 'a t = 'a Map.Make(X).t
val empty : 'a t
val add : X.t -> 'a -> 'a t -> 'a t
val find : X.t -> 'a t -> 'a
val fold : (X.t -> 'a -> 'b -> 'b) -> 'a t -> 'b -> 'b
val equal : ('a -> 'a -> bool) -> 'a t -> 'a t -> bool
end
type t = int XMap.t
val equal : t -> t -> bool
val zeroes : t
val incr : t -> X.t -> t
val to_list : t -> (X.t * int) list
end
=
struct
module XMap = Map.Make( X )

type t = int XMap.t

let equal = XMap.equal ( = )

let zeroes = XMap.empty

let incr map e =
(try succ (XMap.find e map)
with Not_found -> 1)) map

let to_list map = XMap.fold (fun k d a -> (k, d) :: a ) map []

end

module StringCounters = Counters ( String )

let _ =
let l= ["7"; "8192"; "7"; "199"; "199"; "7"; "7"] in
Printf.printf "[\"%s\"] -> %s\n"
(String.concat "\"; \"" l)
(String.concat " + "
(List.map (fun (k, d) -> (string_of_int d) ^ "x\"" ^ k ^ "\"")
(StringCounters.to_list
(List.fold_left StringCounters.incr StringCounters.zeroes l))))

(* -> 1x"8192" + 4x"7" + 2x"199" *)

(* My problem is I want to reject the 'to_list' function (that isn't specific to counting) from Counters functor to an extension of Map :

So I tried to define : *)

module MapPlus ( Map : Map.S ) = struct
include Map

let to_list map = Map.fold (fun k d a -> (k, d) :: a ) map []
end

(*  before Counters, that would be modified this way :
*)
module Counters ( X : Map.OrderedType ) :
sig
module XMap :
sig
type 'a t = 'a Map.Make(X).t
val empty : 'a t
val add : X.t -> 'a -> 'a t -> 'a t
val find : X.t -> 'a t -> 'a
val fold : (X.t -> 'a -> 'b -> 'b) -> 'a t -> 'b -> 'b
val equal : ('a -> 'a -> bool) -> 'a t -> 'a t -> bool
end
type t = int XMap.t
val equal : t -> t -> bool
val zeroes : t
val incr : t -> X.t -> t
end
=
struct
module XMap = MapPlus ( Map.Make( X ) )

type t = int XMap.t

let equal = XMap.equal ( = )

let zeroes = XMap.empty

let incr map e =