* A new `racket/undefined` library exports `undefined` as the value
currently produced by
(letrec ([x x]) x)
This library anticipates a future where that expression will raise
an exception. The `racket/undefined` library will continue to offer
the `undefined` value as a bridge between versions and as a last
* The drawing and GUI libraries provide improved support for
high-resolution bitmaps and their use on Retina displays. For
example, `read-bitmap` includes a `#:try-@2x?` option to trigger
substitutions through the usual "@2x" naming convention.
* Check Syntax cooperates with Typed Racket to show arrows and other
Check Syntax highlighting even when there is a type error.
* Functions provided via contract-out that have first-order contracts
* The contract boundary between typed/untyped modules is much less
expensive. Typed Racket now avoids generating contracts for places
where contracts failures cannot happen.
* Occurrence typing now works better with when/unless. Example:
(let ((x (read)))
(unless (number? x) (error 'bad-input))
* Types in Typed Racket are now pretty-printed.
* Function types can now be written in prefix style, which is now
preferred and is used for printing. Infix function types are still
accepted for backwards compatibility.
* A new `->*' type constructor is used for writing types for functions
with optional and keyword arguments. The notation is similar to the
matching contract combinator.
* Typed Racket forms do not have a `:' suffix by default now. For
example, the `struct' form replaces `struct:'. The suffixed versions
are all provided for backwards compatibility.
* Typed Racket now has preliminary support for classes and
objects. However, it is still experimental and the APIs are subject
* Type aliases in Typed Racket now support recursion and mutual
recursion. For example, `(define-type (MyList X) (U Null (Pair X
(MyList X))))' is now a valid type alias.
* Plot correctly renders intersecting 3D graphs and non-grid-aligned
* Elements in plots output in PDF/PS format have the same relative
scale as in other formats. In particular, it is not necessary to
adjust `plot-font-size` to make PDF plots look the same as PNG.