Re: [Caml-list] Polymorphic Variants

["Lukasz Stafiniak" <lukstafi@gmail.com>]

On 1/16/07, Seth J. Fogarty <sfogarty@gmail.com> wrote:
> On 1/16/07, Tom <tom.primozic@gmail.com> wrote:
> >
> >
> > On 16/01/07, Seth J. Fogarty <sfogarty@gmail.com> wrote:
...
> > using records with overloaded fields and subtyping, so that you could have:
> > type top = {common of string}
> > type one_level_deep = {top | my_only of int}
> >
> > type independent = {my_only of string}
> > so this would be possible:
> > let to_str x -> x.common
> >
> > to_str {common = "first"}; to_str {common = "second"; my_only = 0}
> > ?
>
> OCaml does not, as far as I know, have any structural typing for
> records.. and I am not sure this would be at all cleaner. It might
> WORK, but it would be just as ugly, if not uglier.
>
OCaml has objects, which is a heavy-weight solution to the "structural
subtyping for records" problem. Polymorphic variants make one wonder,
if such light-weight solution could exist for records also, and you
conjecture, that it doesn't. What is the minimal nice version of
structural subtyping for records? Is it objects without classes and
field / method separation (but with late binding)?