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.
In the case that a let rhs doesn't return and therefore the
bodies of the let are unreachable, the bodies need to be marked
as ignored for the optimizer.
In addition, don't attempt unboxed let optimization at all
if the return type is Nothing since it probably means some
body expressions have no type.
Closes GH issue #165
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
Because -let-internal wasn't rename-out'd, users would see its name in
syntax error messages. Adding #:context forces the error messages to be
phrased in terms of the given form.
Since these promises re-evaluate their bodies every time they
are forced, allowing them makes `force` not idempotent and not
safe to treat as a path.
This change is slightly backwards-incompatible, since programs
that previously passed `delay/name` promises across the typed
boundary will now fail at runtime. The alternative is also
incompatible: stop treating `force` as a path. Since `delay/name`
is quite obscure, this approach seems like the safer choice.
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.
