covariance newb question

[Christophe Papazian <christophe.papazian@gmail.com>]

# type +'a t = 'a -> 'a;;
In this definition, expected parameter variances are not satisfied.
The 1st type parameter was expected to be covariant, but it is invariant


But type t seems to be covariant :

# let f : 'a t = (fun x -> x);;
val f : 'a t = <fun>
# let g : int t = f;;
val g : int t = <fun>

Is there something wrong in my thought ?

thank you,

	Christophe Papazian