Question about polymorphic variants

[Xavier Clerc <xcforum@free.fr>]

Hello,

I have a question concerning polymorphic variants and type inference.
Formulating my question from the example of section 4.2 in the ocaml  
manual (version 3.08), I define a function f:

let f = function
| `On -> 1
| `Off -> 0

which is inferred as: val f : [< `Off | `On ] -> int

Then, I use this function in the following expression :

List.map f

which is in turn inferred as: _[< `Off | `On ] list -> int list


My question is about the meaning of the leading underscore in the  
inferred type (given that I understand the meaning of the underscore  
in an expression such as "Stack.create ()" that is inferred as: '_a  
Stack.t).


Regards,

Xavier Clerc