[Caml-list] explicit polymorphic type annotation

[William <r.3@libertysurf.fr>]

Hi,

I don't know how to handle this, and can not find how to do it in the 
manual. I would like "func" to be polymorphic :

let f func =
   Printf.printf "%i\n%!" (func (1,2));
   Printf.printf "%f\n%!" (func (1.,2.));;
f fst;;
f snd;;

=>
Characters 85-87:
Printf.printf "%f\n%!" (func (1.,2.));;
                               ^^
Error: This expression has type float but an expression was expected of 
type int


let f (func:('a. 'a * 'a -> 'a)) =
   Printf.printf "%i\n%!" (func (1,2));
   Printf.printf "%f\n%!" (func (1.,2.));;
f fst;;
f snd;;

=>
Characters 15-16:
let f (func:('a. 'a * 'a -> 'a)) =
                ^
Error: Syntax error: type expected.



Could someone show me how to handle this ?

Also, I did not find any relevant chapter in ocaml.org or ocaml 
reference manual to explain how to do. Any pointers ?

Best regards