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Reference to polymorphic function ?
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Date: -- (:)
From: Ingo Bormuth <ibormuth@e...>
Subject: [SOLVED] Reference to polymorphic function ?

On 2005-09-15 08:48, Jacques Garrigue wrote:
>
> The simplest way to do this is to define a new type:
> 
> type put = {put: 'a -> unit} ;;
> let put = {put = put_to_screen} ;;
> put.put "test";;
> put.put 5;;
> 
Thank you !!! That's exactly what I was looking for.


On 2005-09-14 23:08, Stéphane Glondu wrote:
>
>                                        However, I didn't catch what 
> you want to do with thoses references: maybe there is another way to 
> achieve what you want?
> 

Just for the notes: 

I wrote a serilisation function to pack a quite complex data structure 
into one string. That string is then used to feed a file, socket, 
sha1 or encryption algorithm. 
I want to reduce overhead and directly marshal the values to the 
destination without generating the intermediate string whenever possible.

This is a simple profe of principal prototype :


type data =
  | Int of int
  | Float of float
  | Str of string
;;

type target = 
  | Screen
  | Channel of out_channel
;;

type put =
  {
    str: string -> unit ;
    raw: 'a. 'a -> unit
  }
;;

let serialize data target =
  let put = ref {
        str = ( fun s -> () );
        raw = ( fun v -> () ) } in
  let write_value key value =
    !put.str ( "<" ^ key ^ ">" ) ;
    !put.raw value ;
    !put.str ( "</" ^ key ^ ">" ) in
  let write_data () =
    match data with
     | Int i -> write_value "int" i
     | Float f -> write_value "float" f
     | Str s -> write_value "str" s in
  let init_target =
    match target with
      | Screen -> put := { 
            str = print_string ;
            raw = let f v = print_string ( Marshal.to_string v [] ) in f }
      | Channel chan -> put := { 
            str = output_string chan ;
            raw = let f v = ( Marshal.to_channel chan v [] ) in f } in
  init_target ;
  write_data ()
;;


serialize ( Int 123 ) Screen 
;;

serialize ( Float 3.14 ) Screen 
;;

serialize ( Str "Hello" ) ( Channel ( open_out "/tmp/seri" ) ) 
;;

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