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

[Hugo Ferreira <hmf@inescporto.pt>]

David and Gabriel,

On 05/02/2011 04:15 PM, Gabriel Scherer wrote:
> 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
>

Thank you,
Hugo F.

> On Mon, May 2, 2011 at 4:46 PM, David MENTRE <dmentre@linux-france.org
> <mailto:dmentre@linux-france.org>> wrote:
>
>     Hello Hugo,
>
>     2011/5/2 Hugo Ferreira <hmf@inescporto.pt <mailto: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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