(Racket Tasks On Rosetta Code)

Since (and even before) Asumu Takikawa’s post “200!” at the beginning of March 2013, folk have been beavering away, implementing tasks on Rosetta Code. And on November 15th 2014:

800 tasks have now been Implemented1 in Racket on the Rosetta Code website!

Before I go any further it must be said that, without a doubt… this is awesome! This achievement represents a lot of work, and a lot of code. And everyone who has participated should be thanked and congratulated for getting this far.

So thank you. And well done!


Racket v6.1.1

Racket version 6.1.1 is now available from http://racket-lang.org/

  • 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 install.
  • 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 uses of set! or with-continuation-mark.
  • The compiler performs additional bytecode optimizations. Thanks to Gustavo Massaccesi.
  • The CML library comes with a new replace-evt event constructor. Thanks to Jan Dvořák.
  • Redex's benchmark suite comes with a description of the benchmark programs.
  • Redex's metafunctions can be typeset using the "large left brace" notation for conditionals.
  • The contract library comes with an improved contract-stronger?. Its error messages note that the contract itself might be wrong.
  • The GUI library is DPI-aware on Windows.
  • The openssl library supports Server Name Indication for servers. Thanks to Jay Kominek.
  • The syntax/parse library allows the definition of new pattern forms via pattern expanders, similar to match expanders. Thanks to Alex Knauth.
  • OpenGL on Linux no longer depends on libgtkgl, and core profiles are supported (see set-legacy?).
  • The teaching languages' unit test framework supports check-satisfied, a construct for checking whether a result satisfies a predicate, e.g.:
    (check-satisfied (sort l) sorted?)
Feedback Welcome


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