Dawid Toton wrote: > Why not to just forbid too general 'a ref types? See the example from > the page cited above (with explicit quantifier added): > > let f : forall 'a. 'a -> 'a = > let r : 'a option ref = ref None in > fun x -> (* do evil things with the ref cell *) > let y = !r in > let () = r := Some x in > match y with > | None -> x > | Some y -> y > > The problem is that the 'a variable is bound by a general quantifier and > at the same time it is used to give a type to the ref cell. But if this > were forbidden, I see no need for the value restriction at all. For example: > > let g : forall 'a. 'a -> 'a = > fun (x : exists 'b. 'b) -> > let r : 'b option ref = ref None in > (* nothing bad can happen *) > ...
Nothing useful can happen either. You could never read a value back from r and use/return it as an 'a or for anything else. So why would you want to store it there in the first place? Also, I don't quite understand how your type annotations are supposed to match up. If x : exists 'b. 'b, then f can't be forall 'a. 'a -> 'a. /Andreas -- Caml-list mailing list. Subscription management and archives: https://sympa-roc.inria.fr/wws/info/caml-list Beginner's list: http://groups.yahoo.com/group/ocaml_beginners Bug reports: http://caml.inria.fr/bin/caml-bugs
