Re: [Caml-list] Forcing a Map type: setting the value type

[Gabriel Scherer <gabriel.scherer@gmail.com>]

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My basic idea was to re-export Map using a constrained type. With David
Mentre's insight that only map-producing functions need to be coerced, I
have the following proposal:

module type MonoMap = sig
  include Map.S
  type elt
  val empty : elt t
  val singleton : key -> elt -> elt t
  val of_enum : (key * elt) Enum.t -> elt t
end

module IntMap
  : MonoMap with type key = int with type elt = int
  = struct
    include Map.Make(Int)
    type elt = int
end

On Mon, May 2, 2011 at 4:46 PM, David MENTRE <dmentre@linux-france.org>wrote:

> Hello Hugo,
>
> 2011/5/2 Hugo Ferreira <hmf@inescporto.pt>:
> > Maybe I did not express myself correctly.
> > The above would also work with any other type for the
> > parameter 'a. I want only integers for it. So:
> >
> > # let m = IntMap.empty;;
>
> Just do:
>
>  # let m : int IntMap.t = IntMap.empty;;
>
> The " : int IntMap.t" type annotation restricts the default "'a
> IntMap.t" of IntMap.empty.
>
> > # let m = IntMap.add 1 "42" m;;
>
> Then:
>
>  # let m = IntMap.add 1 "42" m;;
> Characters 26-27:
>   let m = IntMap.add 1 "42" m;;
>                             ^
> This expression has type int IntMap.t but is here used with type
>  string IntMap.t
>
>
> Best regards,
> david
>
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