> This is a good illustration of why -rectypes is not enabled by default.

In my experience, polymorphic recursion is almost always linked to
datatypes whose recursion is itself polymorphic.  As is the case in
Loup's example.

Has there been work in trying to leverage this connection, so that
polymorphic recursion can be automatically inferred by taking advantage of
the implicit type hint provided by the datatype definition?


        Stefan