~/> ocaml -rectypes
         Objective Caml version 3.08.3

   # let rec blackhole x = blackhole;;
   val blackhole : 'b -> 'a as 'a = <fun>

The problem is, though, that almost everything can be typed once you
have unrestricted recursive types (e.g. missing arguments etc), and
consequently many actual errors remain unflagged (which clearly shows
that typing is not only about potential value class mismatches).
Moreover, there are very few practical uses of such a feature, and they
can always be coded easily with recursive datatypes.

It is a pragmatic decision born from experience that you simply do *not
want* to have this, even though you easily could. E.g. for OCaml,
unrestricted recursive typing was removed as default because of frequent
user complaints.

Which is why this actually is a very bad example to chose for dynamic
typing advocacy... ;-)