Re: [Caml-list] Re: module typing issue

[Guillaume Yziquel <guillaume.yziquel@citycable.ch>]

Le Monday 28 Mar 2011 à 09:53:52 (+0200), Alain Frisch a écrit :
> On 03/25/2011 08:01 PM, Guillaume Yziquel wrote:
> >type error = private int
> >
> >external get_error : unit ->  error = "zzz"
> >
> >You get some error level that you can pattern match as an int, and this
> >also enforces that all values of type error come from a call to
> >get_error.
> 
> You need to coerce explicitly from type error to type int (... :>
> int), so this is not really different from defining error as an
> abstract type and exposing a function error->int.
> 
> -- Alain

Yes, doesn't work for private ints. However, it works for stuff like
that, though it's not exactly the same thing as a 'private int':

# type t = private A | B;;
type t = private A | B
# let x : t = Obj.magic 0;;
val x : t = A
# match x with A -> true | _ -> false;;
- : bool = true
# A;;
Error: Cannot create values of the private type t

I thought it also worked on for ints, and in a sense, I'm surprised that
you cannot pattern match private ints as ints without a coercion.

So for enumerating errors coming from C stubs, you can still do it this
way.

-- 
     Guillaume Yziquel