Log Message:
Update to Racket 6.0.1

Changes in version 6.0.1

* 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 resort.

* 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 perform better.

* 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))
      (add1 x))

* 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 to change.

* 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 3D rectangles.

* 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.

Changes in version 6.0

Racket 6.0 has a new package system, including a catalog of
hundreds of already-available packages. Please visit

   http://pkgs.racket-lang.org/

for an overview of the packages.

Racket versions 5.3.4 through 5.3.6 included "beta" versions of the
package system. Racket version 6.0 incorporates many improvements
suggested by preliminary experiences in those versions:

  * A package is treated as a single collection by default, so it is
    even easier to use a GitHub repository as a package. Get started
    quickly:
      http://docs.racket-lang.org/pkg/getting-started.html

  * DrRacket includes a new package manager GUI, available via the
    File|Package Manager ... menu item. The GUI is also available
    as a stand-alone program via the "gui-pkg-manager" package.

  * The main Racket distribution has been separated into about 200
    packages. The Racket installer combines the core system with
    bundled versions of these packages.

    Alternatively, you may now install a Minimal Racket distribution
    --- which is about 1/10 the size of the main distribution --- and
    add only those packages that you need.

  * Package installation supports pre-built packages that include
    compiled byte code and rendered documentation, meaning packages can
    be installed quickly when built versions are available. All
    packages in the main distribution are available in pre-built form.

The recent 5.92 and 5.93 releases served as release candidates for 6.0,
and 6.0 includes a few additional repairs related to the package
system.

Further improvements to the package system are in the works, notably
including package documentation on the package-catalog web site.

COMPATIBILITY NOTE: PLaneT, the previous Racket package system, will
remain in place for the foreseeable future, but we expect all package
work to shift to the new system.

Beyond the package system, this release brings a number of other
changes:

  * Racket's HTML documentation has a new and improved look, thanks to
    Matthew Butterick.

  * The documentation includes a style guide, "How to Program Racket"
    http://docs.racket-lang.org/style/

  * Racket's JIT compiler supports the ARM architecture.

  * Racket supports the Mac's Retina display mode.

  * The performance of the Typed Racket compiler improved by 50% on
    some typed programs.

  * The profiler provides a new mode that uses the errortrace library
    to produce fine-grained profiles.

  * A new contract profiler reports how much time programs spend
    checking contracts, and which contracts are most expensive.

  * The math/flonum library exports fast 105-bit precision operations.

  * Check Syntax handles generated identifiers, especially those
    introduced by struct (e.g. field selectors) and Redex (e.g., e_1,
    e_2)

  * 2htdp/batch-io includes functions for dealing with html/xml in
    files and web sites as X-expressions plus conveniences for
    web-based graph traversals.

  * The `gen:set' generic interface extends set operations to work on
    user-defined types that implement set methods, as well as on other
    set-like built-in types, such as lists.

  * Picts support conversion to SVG format.

  * Under unix, Racket provides desktop entries (.desktop files) for
    its graphical executables.