[Caml-list] Polymorphic hash tables

[Caml-list] Polymorphic hash tables

[Sébastien Hinderer]

Hi,

Is there a way to just replace OCaml's standard hash function for some
tables?

Here is an example:

module MyHashedType : Hashtbl.HashedType = struct
  type t
  let my_n = 20
  let my_m = 30
  let equal = (=)
  let hash = Hashtbl.hash_param my_n my_m
end

module MyHashtbl = Hashtbl.Make(MyHashedType)

let (mytbl : int MyHashtbl.t) = MyHashtbl.create 100

With this example polymorphism seems to be lost and the compiler does
not accept something like
type t = 'a
to retrieve a generic type as for the standard hash tables.

Any suggestion?

Thanks a lot.
Sébastien.

Re: [Caml-list] Polymorphic hash tables

[Goswin von Brederlow]

On Mon, Feb 09, 2015 at 03:21:07PM +0100, Sébastien Hinderer wrote:
> Hi,
> 
> Is there a way to just replace OCaml's standard hash function for some
> tables?
> 
> Here is an example:
> 
> module MyHashedType : Hashtbl.HashedType = struct
>   type t
>   let my_n = 20
>   let my_m = 30
>   let equal = (=)
>   let hash = Hashtbl.hash_param my_n my_m
> end
> 
> module MyHashtbl = Hashtbl.Make(MyHashedType)
> 
> let (mytbl : int MyHashtbl.t) = MyHashtbl.create 100
> 
> With this example polymorphism seems to be lost and the compiler does
> not accept something like
> type t = 'a
> to retrieve a generic type as for the standard hash tables.
> 
> Any suggestion?
> 
> Thanks a lot.
> Sébastien.

You have to use a functor there.

MfG
	Goswin