On Jan 6, 2012, at 07.26 h, Andrej Bauer wrote:
I would be interested to hear what propeties of Ocaml you had to give up to get this interesting extension working? For example, what happens with checking for exhaustivness of match? Caml performs various optimizations in pattern matching, why are those still ok now that new alternatives may appear later?
One such type is already in ML, for historical reasons it happens to be named exn. Consequently, you don't really give up anything, your questions already apply to the exception type. Exhaustiveness simply requires a catch-all in all pattern matches over this type. More difficult is irredundancy, because constructors can be aliased without the type system tracking that (and it cannot across module boundaries). You have to give up there.
Generalising exn this way is an old idea, e.g. we implemented it in Alice ML. The standard reply to requesting such an extension is that it's not really needed, because you can already do everything using exn (though without custom type distinctions, and minus GADTs in OCaml).
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