PLT Redex Summer School, Call for Participation

LOCATION: University of Utah, Salt Lake City
DATES: July 27 - July 31, 2015

PLT Redex is a lightweight, embedded DSL for modeling programming
languages, their reduction semantics, and their type systems. It comes with
an IDE and a toolbox for exploring, testing, debugging, and type-setting
language models. The PLT research group has successfully used Redex to
model and analyze a wide spectrum of published models.

The summer school will introduce students to the underlying theory of
reduction semantics, programming in the Redex language, and using its
tool suite effectively.  The course is intended for PhD students and
researchers in programming languages. Enrollment is limited to 25

While the workshop itself is free, attendees must pay for travel, room, and
board. We expect room and board to be around $500, assuming an arrival in
the evening of Sunday July 26 and leaving Friday July 31 or August 1.
Partial financial support for PhD students is available.

To register, send email to Matthew Flatt (mflatt@cs.utah.edu). If you
are a PhD student and requesting financial support, CC your advisor
and ask for a one-line confirmation email.


  Matthias Felleisen, Robert Bruce Findler, Matthew Flatt.
  Semantics Engineering with PLT Redex. MIT Press, 2012.

  Casey Klein, John Clements, Christos Dimoulas, Carl Eastlund,
  Matthias Felleisen, Matthew Flatt, Jay McCarthy, Jon Rafkind, Sam
  Tobin-Hochstadt, Robert Bruce Findler. Run Your Research: On the
  Effectiveness of Lightweight Mechanization. POPL 2012.


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 control over the timing of flushes (i.e., a composable atexit). New functions include current-plumber, plumber-add-flush!, and plumber-flush-all.
  • Contracts: the contract system's random testing facility has been strengthened so that it can easily find simple mistakes in contracted data structure implementations (e.g. an accidental reverse of a conditional in a heap invariant check).
  • Redex: the semantics of mis-match patterns (variables followed by _!_) inside ellipses has changed in a backwards-incompatible way. This change simplifies the patterns' semantics and increases the usefulness of these patterns.
  • Teaching languages: check-random is an addition to the preferred unit testing framework in the teaching languages. It enables the testing of students' functions that use random-number generation. (Thanks to David Van Horn (UMaryland) for proposing this idea.)
  • Upgraded and normalized versions of graphics libraries and dependencies (Pango, Cairo, GLib, etc.) that are bundled with Racket on Windows and Mac OS X. For example, FreeType support is consistently enabled.
  • Typed Racket: its standard library includes contracted exports from the Racket standard library, such as the formatting combinators of racket/format. It also supports Racket's asynchronous channels; see the typed/racket/async-channel library.
  • SSL: The openssl library supports forward secrecy via DHE and ECDHE cipher suites (thanks to Edward Lee) and Server Name Indication (thanks to Jay Kominek).
  • The mzlib/class100 library has been removed. Use racket/class instead.


Scheme Workshop 2014

DEADLINE: 5 September 2014, (23:59 UTC-12)
WEBSITE: http://homes.soic.indiana.edu/jhemann/scheme-14/
LOCATION: Washington, DC (co-located with Clojure/conj)
DATE: 19 November 2014

The 2014 Scheme and Functional Programming Workshop is calling for

Submissions related to Scheme and functional programming are welcome
and encouraged. Topics of interest include but are not limited to:

  • Program-development environments, debugging, testing
  • Implementation (interpreters, compilers, tools, benchmarks, etc)
  • Syntax, macros, and hygiene
  • Distributed computing, concurrency, parallelism
  • Interoperability with other languages, FFIs
  • Continuations, modules, object systems, types
  • Theory, formal semantics, correctness
  • History, evolution and standardization of Scheme
  • Applications, experience and industrial uses of Scheme
  • Education
  • Scheme pearls (elegant, instructive uses of Scheme)

We also welcome papers related to dynamic or multiparadigmatic
languages and programming techniques.

Full papers are due 5 September 2014.
Authors will be notified by 10 October 2014.
Camera-ready versions are due 24 Oct 2014.
All deadlines are (23:59 UTC-12), "Anywhere on Earth".

For more information, please see:


See you there!


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-@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.


Registration for (fourth RacketCon)

Registration for (fourth RacketCon) is now open. Tickets are 30$.


(fourth RacketCon) will be held on September 20th, and will be co-located with Strange Loop in St. Louis.

RacketCon is a yearly event where members of the Racket community get together, featuring talks and demos about the things you do with Racket.

To get you excited, here's a sneak peek at the roster of speakers so far:

  • Michael Fogus (keynote)
  • Matthew Butterick
  • Matthew Flatt
  • Jay McCarthy
  • Daniel Prager
  • Neil Toronto
We still have room for more speakers. If you've built something cool with Racket, we want to hear about it! Hope to see you there! Vincent, for the Racket team


The new Racket home page

Racket now has a new look for its web presence. You can see it at http://racket-lang.org (modulo DNS propagation).

The new pages improve on the old in several ways:

  • More information is now on the front page.
  • The site works much better small devices, such as phones.
  • It's easier to find important parts of the site, like the package directory.
  • The download process is more streamlined -- now it's only 2 clicks.

We also wanted to have a new look, and a description that talks about why Racket is exciting.

Finally, we've taken this opportunity to shift our web hosting entirely to Amazon S3, for which Greg Hendershott's aws package has been very helpful.

While the new pages have been under development for quite a while, we're still happy to take bug reports, suggestions and (especially) patches: all of the site can be found here:
with the framework for building the site here:

The site is built using Eli's scribble/html library, which is very nice to use.

I'd especially like to thank Eli and Matthew for their help with this -- going from my hacked-up HTML prototype to the smooth-building and well-organized code we have now has taken lots of work.



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 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".
  • 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; e.g., see http://bit.ly/1d0Ye4z
  • 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.