Racket v6.7

Racket version 6.7 is now available from http://racket-lang.org/

  • Racket supports building graphical applications on Android through the racket-android project: https://github.com/jeapostrophe/racket-android
  • The Racket REPL comes with line-editing, command and result history, and various meta-commands out of the box, via the racket/interactive module. See the racket/interactive and xrepl documentation for details.
  • The package system supports authentication when installing packages from git, using the raco pkg config git-checkout-credentials configuration option.
  • HTTP libraries, as well as raco pkg, support proxying via HTTP CONNECT.
  • Typed Racket provides typed versions of racket/os and racket/db/sqlite.
  • The PLT_COMPILED_FILE_CHECK environment variable provides more fine-grained control over when .zo files are consulted.
  • The documentation search supports searching for #langs and #readers via the "L:" and "R:" search prefixes.
  • The file/glob module implements globbing for path-strings.
  • Optimizations in the bytecode compiler improve performance for structure, list, string, and byte-string operations.
The following people contributed to this release:
Alex Knauth, Alex Harsanyi, Alexis King, Andrew Kent, Asumu Takikawa, Ben Greenman, Brian Lachance, Chongkai Zhu, Daniel Feltey, Georges Dupéron, Gustavo Massaccesi, Jay McCarthy, John Clements, Jonathan Schuster, Leif Andersen, Marc Burns, Matthew Butterick, Matthew Flatt,
Matthias Felleisen, Mike Sperber, Robby Findler, Rohin Shah, Ryan Culpepper, Sam Tobin-Hochstadt, Spencer Florence, Stephen Chang, Stephen De Gabrielle, Tim Brown, Tony Garnock-Jones, Vincent St-Amour, WarGrey Gyoudmon Ju, and William J. Bowman.

Feedback Welcome


Racket v6.6

Racket version 6.6 is now available from http://racket-lang.org/

  • 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 types.
  • 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 terminate.
  • htdp/dir: The create-dir function delivers data information for files in a new field. The domain of its functions are backwards compatible.

The following people contributed to this release:
Alex Knauth, Alexander Shopov, Alexis King, Andrew Kent, Asumu Takikawa,
Ben Greenman, Bernardo Sulzbach, Brian Lachance, Chris Jester-Young, Dan
Feltey, Eric Dobson, Georges Dupéron, Gustavo Massaccesi, James Bornholt,
Jay McCarthy, John Clements, Leandro Facchinetti, Leif Andersen, Maksim
Kochkin, Matthew Flatt, Matthias Felleisen, Mike Sperber, Paul Stansifer,
Pedro Caldeira, Philip McGrath, Robby Findler, Ryan Culpepper, Sam
Tobin-Hochstadt, Spencer Florence, Stephen Chang, Stephen De Gabrielle,
Tim Brown, Tony Garnock-Jones, Vincent St-Amour, WarGrey Gyoudmon Ju,
William J. Bowman, and Zeina Migeed.

Feedback Welcome


Racket v6.5

Racket version 6.5 is now available from http://racket-lang.org/

  • Typed Racket and the racket/contract library generate code with lower overhead, speeding up typed/untyped interaction in a number of gradual typing programs we studied.
  • Macros written using syntax-parse automatically emit more accurate error messages.
  • The contract profiler captures costs from more contract combinators, including all those in the main distribution.
  • Hash table and set iteration, via both existing and new non-generic sequences, is more performant, up to twice as fast on microbenchmarks.
  • The Racket optimizer detects many more optimization opportunities, including when variables always hold numbers.
  • The db library supports single-result CALL statements in MySQL.
  • The net/dns library supports SRV records.
  • The racket/unix-socket library supports listen and accept operations.

The following people contributed to this release:
Adrien Tateno, Alex Knauth, Alexander Shopov, Alexis King, Andrew Kent, Asumu Takikawa, Ben Greenman, Chen Xiao, Chris Jester-Young, Daniel Feltey, Eric Dobson, Georges Dupéron, Gustavo Massaccesi, Ian Harris, Jay McCarthy, Jens Axel Søgaard, John Clements, Leandro Facchinetti, Lehi Toskin, Leif Andersen, Łukasz Dąbek, Marc Kaufmann, Matthew Flatt, Matthias Felleisen, Michael McConville, Mike Sperber, Paul Stansifer, Philippe Meunier, Robby Findler, Rodrigo Setti, Ryan Culpepper, Sam Caldwell, Sam Tobin-Hochstadt, Sorawee Porncharoenwase, Spencer Florence, Stephen Chang, Tony Garnock-Jones, Vincent St-Amour, WarGrey Gyoudmon Ju, and William J. Bowman.

Feedback Welcome


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 version.

The vulnerability affects web servers that serve static files using the #:extra-files-paths 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 here. Then run:

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

If you need advice on updating Racket installations older than version 6.0, please let us know and we will provide them.

To test that your Racket installation is fixed, you can run the program here. It will print whether your installation is out of date.

Racket v6.4

Racket version 6.4 is now available from http://racket-lang.org/

  • 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 this post.
  • 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 implementation.
  • The default package catalog is an HTTPS address instead of HTTP, and package operations properly validate server certificates when using HTTPS.
  • Documentation may define their own categories for the manual top-level page by using strings, rather than only symbols that name pre-defined categories.
  • The Racket cheat sheet is included in the main distribution.
  • DrRacket is available in Bulgarian, thanks to Alexander Shopov.
  • The contract Typed Racket generates for the Any type is more permissive, allowing more typed/untyped programs to work without contract errors.
  • Redex supports binding specifications; describe which variables bind in which expressions and your metafunctions and reduction relations automatically become scope-sensitive. Thanks to Paul Stansifer for this improvement.
  • All pict functions accept pict-convertibles. This allows for transparent interoperability between pict and libraries like 2htdp/image.
  • The raco profile and raco contract-profile commands provide easy access to profiling tools, without requiring program modifications.
Feedback Welcome


Racket v6.3

Racket version 6.3 is now available from http://racket-lang.org/

  • Racket's macro expander uses a new representation of binding called "set of scopes". The new binding model provides a simpler explanation of how macros preserve binding, especially across module boundaries and in hygiene-bending expansions. The new expander is mostly compatible with existing Racket macros, but there are some incompatibilities. For the formally inclined, a research paper on this macro system will appear at POPL next year: http://www.cs.utah.edu/plt/scope-sets/
  • Racket's GUI library now uses Gtk+ 3 when available, instead of Gtk+ 2. Set the PLT_GTK2 environment variable to select Gtk+ 2.
  • Added a new Redex tutorial based on a week-long workshop in SLC.
  • Better syntax error checking for Redex patterns that do not use holes correctly.
  • The blueboxes are more agressive about finding names to look up in the docs, meaning they are useful much more often.
  • Submodules are now fully supported in Typed Racket. Previously, some uses of submodules would produce internal errors, making it hard to module+ test and module+ main effectively in Typed Racket. The switch to the set-of-scopes expander fixed these problems, and submodules are now happily at home in Typed Racket.
  • The typed/racket/unsafe library provides import and export forms that circumvent contract generation. This improves performance for typed-untyped interaction at the cost of safety and debuggability.
  • Typed Racket provides experimental support for units (from racket/unit).
  • The experimental define-new-subtype form allows overlaying finer distinctions between otherwise identical types, similar to Haskell's new type.
  • The Promise type constructor changes in a backwards-incompatible way to exclude promises created with promise/name.
  • The unstable-* packages are out of the main distribution. Most of their contents have been either merged with established Racket libraries or spun off as their own packages. This change is backwards compatible for packages that properly list their dependencies. Full details: http://blog.racket-lang.org/2015/10/retiring-unstable.html
  • edu: big-bang supports a display-mode clause so that world programs can take over the entire screen.
Feedback welcome


Retiring unstable

Some of you may be familiar with the unstable collection, whose
purpose was to serve as a staging ground for new APIs that hadn't yet
found a more permanent home. With the advent of the package system,
packages can serve that same purpose, which removes the need for a
dedicated unstable collection provided by the main distribution.

For this reason we are moving unstable-* packages out of the main

For backwards compatibility, the packages remain available from the
package catalog. Packages that properly list their dependencies (as they
should! it's an error not to!) are unaffected by this change. Packages
that are missing dependencies may need to be adjusted to include the
appropriate unstable dependencies.

The unstable packages contained many useful functions and APIs, and we
merged many of them into established Racket libraries. Others were spun
off as their own packages. The remaining APIs, which we judged too
narrow or too immature, we left in unstable packages, where they are
still available in their original form. In all cases, the original
unstable libraries continue to export the same bindings they always
did, to ensure backwards compatibility.

For completeness, here is a list of the fate of each unstable library
that used to be part of the main distribution.

  • unstable/2d

    • Moved to the 2d package.
  • unstable/arrow

    • Left in unstable-lib.
  • unstable/automata

    • Moved to the automata package.
  • unstable/bytes

    • Left in unstable-lib.
  • unstable/class-iop

    • Moved to the class-iop package.
  • unstable/contract

    • Moved non-empty-string? to racket/string.
    • Moved port-number? and tcp-listen-port? to racket/tcp, the
      latter renamed to listen-port-number?.
    • Moved if/c, failure-result/c, predicate/c and
      rename-contract to racket/contract.
    • Moved treeof to plot/utils.
    • Moved sequence/c to racket/sequence.
    • Left path-piece?, maybe/c, truth/c in unstable-contract-lib.
  • unstable/custom-write

    • Moved make-constructor-style-printer to racket/struct.
    • Left prop:auto-custom-write in unstable-lib.
  • unstable/debug

    • Left in unstable-debug-lib.
  • unstable/define

    • Left in unstable-lib.
  • unstable/error

    • Left in unstable-lib.
  • unstable/find

    • Left in unstable-lib.
  • unstable/flonum

    • Superceded by math/flonum. Left in unstable-flonum-lib.
  • unstable/function

    • Merged with racket/function.
  • unstable/future

    • Merged with racket/future.
  • unstable/gui/notify

    • Moved to framework/notify, with naming changes.
  • unstable/gui/pict

    • Moved color/c, light, dark, red, orange, yellow, green,
      blue, purple, black, brown, gray, white, cyan, and
      magenta to pict/color.
    • Moved show, hide, pict-if, pict-cond, and pict-case to
    • Merged scale-to with pict's scale-to-fit.
    • Merged ellipse/border, circle/border, rectangle/border,
      rounded-rectangle/border with pict's ellipse, circle,
      rectangle, and rounded-rectangle, respectively.
    • Merged pin-label-line, pin-arrow-label-line, and
      pin-arrows-label-line with pict's pin-line, pin-arrow-line,
      and pin-arrows-line, respectively.
    • Moved blur, shadow, and shadow-frame to pict/shadow.
    • Moved unstable/gui/pict/align to ppict/align, in the ppict
    • Left color, pict-match, pict-combine, with-pict-combine,
      fill, strike, shade, blur-bitmap!, arch,
      draw-pict-centered, backdrop, cross-out, and
      make-plt-title-background in unstable-lib.
  • unstable/gui/ppict

    • Moved to the ppict package.
  • unstable/gui/prefs

    • Moved to framework/preferences, with naming changes.
  • unstable/gui/redex

    • Left in unstable-redex.
  • unstable/gui/scribble

    • Left in unstable-lib.
  • unstable/gui/slideshow

    • Moved with-size, with-scale, big, small, with-font,
      with-style, bold, italic, subscript, superscript, caps,
      and blank-line to slideshow/text.
    • Moved slide/staged, staged, stage, stage-name, at,
      before, after, before/at, after/at to the staged-slide
    • Left column, columns, column-size, two-columns,
      mini-slide, tabular, reveal, revealing-slide, and
      items-slide in unstable-lib.
  • unstable/gui/snip

    • Left in unstable-lib.
  • unstable/hash

    • Merged with racket/hash.
  • unstable/latent-contract

    • Left in unstable-latent-contract-lib.
  • unstable/lazy-require

    • lazy-require has been in racket/lazy-require for some time.
    • Left begin-on-demand in unstable-lib.
  • unstable/list

    • Moved check-duplicates, remf, remf*, group-by,
      cartesian-product, list-update, and list-set to racket/list.
    • Moved list-prefix?, take-common-prefix, drop-common-prefix,
      and split-common-prefix to racket/list, with slight API changes
      to harmonize with Racket's list API.
    • Left filter-multiple, extend, map/values, and map2 in
  • unstable/logging

    • Moved with-intercepted-logging and with-logging-to-port to
    • Left start-recording and stop-recording in unstable-lib.
  • unstable/macro-testing

    • Moved to syntax/macro-testing.
  • unstable/markparam

    • Moved to the markparam package.
  • unstable/open-place

    • Moved open-place to racket/place, and renamed it place/context.
  • unstable/options

    • Moved to the option-contract package.
  • unstable/parameter-group

    • Moved to the parameter-group package.
  • unstable/pretty

    • Merged pretty-format/write, pretty-format/display, and
      pretty-format/print with racket/pretty's pretty-format.
    • Left break-lines in unstable-pretty-lib.
  • unstable/recontract

    • Merged with racket/contract some time ago.
  • unstable/sandbox

    • Merged with scribble/eval.
  • unstable/sequence

    • Moved in-syntax and in-slice to racket/sequence.
    • Left in-pairs, in-sequence-forever, and sequence-lift in
  • unstable/socket

    • Moved to the unix-socket package.
  • unstable/string

    • Left in unstable-lib.
  • unstable/struct

    • Moved struct->list to racket/struct.
    • Left make in unstable-lib.
  • unstable/syntax

    • Moved make-variable-like-transformer to syntax/transformer.
    • Moved syntax-source-directory and syntax-source-file-name to
    • Left explode-module-path-index, phase-of-enclosing-module,
      format-unique-id, syntax-length, and syntax-within? in
  • unstable/temp-c

    • Moved to the temp-c package.
  • unstable/time

    • Left in unstable-lib.
  • unstable/wrapc

    • Moved to syntax/contract.