[Caml-list] Why doesn't relaxed value restriction apply here?

[Romain Bardou <romain@bardou.fr>]

Hello,

According to the manual 
(http://caml.inria.fr/pub/docs/manual-ocaml/polymorphism.html) and to 
the paper "Relaxing the Value Restriction" 
(http://caml.inria.fr/pub/papers/garrigue-value_restriction-fiwflp04.pdf), 
the relaxed value restriction allows to generalize type variables which 
only appear in covariant positions.

The following code :

     let f = let _ = ref 0 in fun f -> f []

returns the following in the toplevel:

     val f : ('_a list -> '_b) -> '_b = <fun>

In this type, '_a only appears in covariant position. So, why is it not 
generalized?

Sorry if this has been asked already, I could not find anything. I'm 
sure there is a simple explanation. I can't find out whether:
- I'm stupid and '_a actually appears in a non-covariant position;
- I'm stupid and read the rule about relaxed value restriction wrong;
- or the relaxed value restriction which was implemented is not actually 
the one which is described in the manual and in the paper.

Cheers,

-- 
Romain Bardou