Re: [Caml-list] Reference to polymorphic function ?

[Jacques Garrigue <garrigue@math.nagoya-u.ac.jp>]

From: Ingo Bormuth <ibormuth@efil.de>

> Nevertheless, if I store the polymorphic function in a reference to 
> create a closure for all kinds of output methodeis, any attemps to use
> that function are thwarted by the type interferer.
> 
>     # let put = ref put_to_screen ;;
>     val put : ('_a -> unit) ref = {contents = <fun>}
> 
>     # !put "test" ;;
>     %%%%%%test- : unit = ()
> 
>     # !put 5 ;;
>     This expression has type int but is here used with type string
> 
> How can I keep the interferer from explicitly resolving the type of v ?

You cannot: this would be unsound.
Actually, this is the opposite: you want to tell in advance the
inferer that put is polymorphic, and that only polymorphic values
should be accepeted. 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;;

---------------------------------------------------------------------------
Jacques Garrigue      Nagoya University     garrigue at math.nagoya-u.ac.jp
		   <A HREF=http://www.math.nagoya-u.ac.jp/~garrigue/>JG</A>