Vincent St-Amour | 23 Jul 01:51 2016

Racket v6.6

Racket version 6.6 is now available from

- The new Macro Profiler command-line tool (`raco macro-profiler`) shows
  how macros contribute to the final expanded code size of a program.

- Typed Racket supports intersection types. This allows the type system
  to track more information, and for programmers to express more precise

- Typed Racket produces up to 4x smaller compiled files compared with
  Racket 6.5, reducing the size of the Racket distribution by 50M.

- Typed Racket issues warnings in cases where the contract generated for
  `Any` was not strict enough in the past. These warnings will become
  errors in a future release. Warnings are enabled via View -> Show Log
  in DrRacket, and shown by default on command-line Racket.

- Typed Racket enforces uses of `cast` more correctly, by checking both
  the "casted-to" and "casted-from" types. Previously, only the former
  were checked. In some cases, this will produce contract errors in
  programs that did not have errors before.

- `syntax-parse` raises an error when an ellipsis pattern has an empty
  match rather than diverging, and it logs a warning when it statically
  detects a nullable pattern, such as `((~seq) ...)`. In the next version
  of Racket, it will reject the pattern instead, and it will remove
  special handling that currently makes some uses of such patterns
(Continue reading)

Ryan Culpepper | 8 Feb 17:13 2016

Racket v6.4

Racket version 6.4 is now available from

- We fixed a security vulnerability in the web server.  The existing
   web server is vulnerable to a navigation attack if it is also
   enabled to serve files statically; that is, any file readable by
   the web server is accessible remotely. For more information see

- DrRacket's scrolling is faster.

- Incremental garbage-collection mode can eliminate long pauses in a
   program. For example, incremental mode is useful for avoiding pauses
   in games and animations.

   Programs must specifically request incremental mode with
   `(collect-garbage 'incremental)`, but libraries such as
   `2htdp/universe` include the request as part of the library's

- The default package catalog is an HTTPS address instead of HTTP, and
   package operations properly validate server certificates when using

- Documentation may define their own categories for the manual top-
   level page by using strings, rather than only symbols that name
   pre-defined categories.

(Continue reading)

Sam Tobin-Hochstadt | 8 Feb 17:17 2016

Racket Web Server Security Vulnerability

We recently discovered a serious security vulnerability in the Racket
web server, which can lead to unintended disclosure of files on the
machine running the web server. This vulnerability is fixed in Racket
version 6.4, just released, and we encourage people to upgrade to that

The vulnerability affects web servers that serve static files using
the `#:extra-static-files` option, including the default value of this
option. If you do not use the Racket web serve to serve static files,
or you do so via a mechanism that does not use the `make-url-≥path`
function, then you are likely not vulnerable. Affected web serves will
allow specially-crafted URLs to access files outside of the specified
paths, potentially exposing any file that the web server process is
able to read.

If you cannot immediately upgrade to version 6.4, we have provided a
package catalog with updated versions of the "web-server-lib" package
for versions of Racket back to 6.0. That catalog is located at

To use it to upgrade your Racket installation, add it as a catalog
using `raco pkg config`. To make this process easier, you can download
the Racket script available at Then run:

  $ racket add-catalog.rkt
  $ raco pkg update -i web-server-lib

On some systems, this may need to be run with administrator or
(Continue reading)

Ryan Culpepper | 10 Aug 23:54 2015

Racket v6.2.1

Racket version 6.2.1 is now available from

Version 6.2.1 patches the recent v6.2 release in three small ways:

* For the How to Design Programs teaching languages, DrRacket offers
   an option to use the old style for printing the constants `true`,
   `false`, and `empty` instead of `#true`, `#false`, and `'()`.

* The teaching languages come with some additional functions to match
   the August 2015 stable release of HtDP 2nd edition.

* A repair to the compiler avoids an infinite loop at compile time for
   certain expressions that should loop forever at run time.

Feedback Welcome
  Racket Announcements list:

Ryan Culpepper | 20 Jun 05:21 2015

Racket v6.2

Racket version 6.2 is now available from

With this release we are taking a major step forward to get our user
community even more involved than in the past. Over the past six months,
we have re-organized the Racket code base into a small core code repo
and many other package repos, all found on GitHub. If you have time and
if you wish to get involved, please take a look at the GitHub repos and
find your favorite places to learn, fix, and enhance our world.

The core repo is at, and the
package repos are listed at

core repo

* The package manager supports a direct references to Git repositories
   via "git://[...]", "http://[...].git", and "https://[...].git" URLs.
   (Previously, only references to GitHub were supported.)

* A `--clone` option for `raco pkg install` or `raco pkg update`
   facilitates Git-based package development. If a package X has a Git
   repository source, installing and updating the package pulls from the
   repository in a read-only mode. Using `raco pkg update --clone X`
   switches the local installation to a repository checkout that is
   suitable for modifying the package implementation, issuing pull
   requests, pushing changes, and so on.

   Using `raco pkg update --lookup X` switches the package back to the
   default installation mode.
(Continue reading)

Ryan Culpepper | 4 Nov 16:46 2014

Racket v6.1.1

Racket version 6.1.1 is now available from

* The MAC OS X YOSEMITE compatibility problems are fixed. We
   bundled a patched Pango text-drawing library with Racket.

* The WINDOWS [32-bit] releases fixes the window-update crashes.
   We bundled a patched Cairo drawing library with Racket.

* TYPED RACKET closes two safety holes in the exception system.
   The revised type system restricts `raise' to send only
   instances of the `exn' structure type and flat data to
   handlers. It also checks exception handlers properly.
   NOTE: Previously well-typed programs may fail to typecheck.

* TYPED RACKET'S typed regions support casts and predicates.

* 2HTDP/IMAGE'S notion of equality ignores an image's baseline.

* The PACKAGE MANAGER supports a binary library installation mode,
   which allows users to install packages without source or
   documentation.  Use the `--binary-lib' option with `raco pkg

* The new DRRACKET-TOOL-LIB package factors out parts of DrRacket's
   IDE so that they can be reused with other editors, such as Emacs.

* The COMPILER'S use-before-defined analysis has been repaired for
   certain forms of nested `letrec', some `let' forms, and some
(Continue reading)

Ryan Culpepper | 2 Aug 20:35 2014

Racket v6.1

PLT Design Inc. announces the release of Racket version 6.1 at

The MAJOR INNOVATION concerns local recursive variable definitions.
Instead of initializing variables with an `undefined' value, Racket
raises an exception when such a variable is used before its definition.
(Thanks to Claire Alvis for adapting Dybvig's "Fixing Letrec" work.)

Since programs are rarely intended to produce #<undefined>, raising an
exception provides early and improved feedback. Module-level variables
have always triggered such an exception when used too early, and this
change finally gives local bindings --- including class fields --- the
same meaning.

This change is backwards-incompatible with prior releases of Racket.
Aside from exposing a few bugs, the change will mainly affect programs
that include

(define undefined (letrec ([x x]) x))

to obtain the #<undefined> value. In its stead, Racket provides the same
value via the `racket/undefined' library (which was introduced in the
previous release). Programmers are encouraged to use it in place of the
pattern above to obtain the "undefined" value.

The release also includes the following SMALL CHANGES:

* PLUMBERS generalize the flush-on-exit capability of primitive output
   ports to enable arbitrary flushing actions and to give programmers
(Continue reading)

Ryan Culpepper | 8 May 22:50 2014

Racket v6.0.1

Racket version 6.0.1 is now available from

* 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- <at> 2x?` option to trigger
   substitutions through the usual " <at> 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:
(Continue reading)

Ryan Culpepper | 27 Feb 00:01 2014

Racket v6.0

Racket version 6.0 is now available from

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

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

   * 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
(Continue reading)

Eli Barzilay | 10 Aug 14:59 2013

Racket v5.3.6

Racket version 5.3.6 is now available from

Racket v5.3.6 is a bug-fix release.  It eliminates errors from
v5.3.5 that people have found over the summer.

Feedback Welcome,

          ((lambda (x) (x x)) (lambda (x) (x x)))          Eli Barzilay:
                             Maze is Life!
  Racket Announcements list:

Eli Barzilay | 18 Jun 13:20 2013

Racket v5.3.5

Racket version 5.3.5 is now available from

This is a special-purpose release to match the arrival of "Realm of
Racket" in bookstores.  Racket v.5.3.5 adds a single `realm'
collection to the v5.3.4 release.  The new collection contains the
source code that readers of Realm may wish to use for experiments.

Feedback Welcome,

          ((lambda (x) (x x)) (lambda (x) (x x)))          Eli Barzilay:
                             Maze is Life!
  Racket Announcements list: