Most unit forms are supported, including most of the "infer" forms that
infer imports/exports/linkages from the current context.
Notably, none of the structural linking forms for units are supported, and
`define-unit-binding` is also currently unsupported.
The old check was broken for cases with type constructors
with more than one type argument and was also too conservative
in some cases (e.g., when one cycle refers to another cycle of
aliases in a non-recursive manner).
The new check is still conservative, but it allows more types
than before.
Closes GH issue #157
This enables contract generation in the negative
direction (untyped->typed) for row polymorphic types
(basically mixin types).
Depends on `class-seal` and `class-unseal` in
the racket/class library.
This helped for debugging, especially since some of
the comments were inaccurate. Removed contract comments
that aren't more specific than the code contracts.
When exporting row polymorphic functions from TR, just
use absent clauses to ensure that TR won't accidentally
try to add pre-existing fields/methods. No sealing is
needed because the typechecker enforces parameteric use
of the class.
Instead of registering aliases before we find out if they are
recursive or not, register them after that information is found.
That avoids spurious aliases that end up in the type name
environment without the need for a `remove-type-name` operation.
For unions of multiple type aliases the new placeholder
would cause union collapsing incorrectly. Put an uninterned
symbol in the placeholder types to avoid this.
