]> On Thursday, Jul 24, 2003, at 18:28 US/Pacific, Karl Zilles wrote: > james woodyatt wrote: >> I'm specifically excited about the polymorphic generalization of >> covariant parts of expansive expressions. > > I read about this in the changes document, but I'm unable to wrap my > head around it. > > > For instance, if f: unit -> 'a list, "let x = f ()" > > gives "x" the generalized type forall 'a. 'a list, instead of '_a > list > > as before. > > Can someone simplify this for me? Under what circumstances would this > be useful? Sure. I see it with functors. Consider the following example: # module type X = sig type +'a t val f: unit -> 'a t end;; This is a module type I plan to use as the input to a functor. The top responds with this following: module type X = sig type +'a t val f : unit -> 'a t end So, imagine you want to write a functor like so: # module Y(X: X) = struct let x = X.f () end;; Here's what the 3.06 top-level says is the type of that module: module Y : functor (X : X) -> sig val x : '_a X.t end Here's what the 3.07+beta1 version says: module Y : functor (X : X) -> sig val x : 'a X.t end This is so much better. In the 3.06 case, I get a module whose type isn't complete yet. In the 3.07+beta1 case, I get a module whose type is complete. With 3.06, I have to write 'x' as a function that returns a constructed object every time I call it. With 3.07+beta1, I can write 'x' as a value that gets constructed once when the functor is called. -- j h woodyatt <jhw@wetware.com> that's my village calling... no doubt, they want their idiot back. ------------------- To unsubscribe, mail caml-list-request@inria.fr Archives: http://caml.inria.fr Bug reports: http://caml.inria.fr/bin/caml-bugs FAQ: http://caml.inria.fr/FAQ/ Beginner's list: http://groups.yahoo.com/group/ocaml_beginners