On Mon, Jun 7, 2010 at 11:22 AM, Daniel Bünzli
<daniel.buenzli@erratique.ch> wrote:
> That's true and certainly a good argument for the second form if you
> already know the type of your annotations and have such needs. However
> if you want to keep that polymorphic (the annotation is a convenience
> for the client) it results in a type variable per case which becomes
> heavy.

You probably know that already but there is a nice use of object types
as "type-level records" that make that kind of "lots of type
variables" situations tractable :

type 'annot tree =
 | Leaf of 'leaf_annot * string
 | Node of 'node_annot * 'annot tree list
constraint 'annot =
 < leaf : 'leaf_annot;
   node : 'node_annot >