[Racket announcement] Racket v7.2

Racket version 7.2 is now available from

    http://racket-lang.org/

Racket-on-Chez is done in a useful sense, but we'll wait until it gets
better before making it the default Racket implementation. For more
information, see

    http://blog.racket-lang.org/2019/01/racket-on-chez-status.html

In addition, the Racket 7.2 release includes the following improvements,
which apply to both implementations:

- The contract system supports collapsible contracts, which avoid
  repeated wrappers in certain pathological situations. Thanks to Daniel
  Feltey.

- Quickscript, a scripting tool for DrRacket, has become part of the
  standard distribution. Thanks to Laurent Orseau.

- The web server's built-in configuration for serving static files
  recognizes the ".mjs" extension for JavaScript modules.

- The `data/enumerate` library supports an additional form of
  subtraction via `but-not/e`, following Yorgey and Foner's ICFP'18
  paper. Thanks to Max New.

- The `letrec.rkt` example model in Redex has been changed to more
  closely match Racket, which led to some bug fixes in Racket's
  implementation of `letrec` and `set!`.

- The racklog library has seen a number of improvements, including fixes
  to logic variable binding, logic variables containing predicates being
  applicable, and the introduction of an `%andmap` higher-order predicate.

The following people contributed to this release:
Akihide Nano, Alex Feldman-Crough, Alexander McLin, Alexander Shopov,
Alexis King, Alex Knauth, Andrew Kent, Asumu Takikawa, Ben Greenman,
Bogdan Popa, Caner Derici, Chongkai Zhu, Dan Feltey, Darren Newton, Gan
Shen, Greg Hendershott, Gustavo Massaccesi, Jay McCarthy, Jens Axel
Søgaard, John Clements, Jordan Johnson, Kevin Robert Stravers, Leif
Andersen, Leo Uino, Matt Kraai, Matthew Butterick, Matthew Flatt,
Matthias Felleisen, Max New, Michael Burge, Mike Sperber, Paul
C. Anagnostopoulos, Paulo Matos, Philip McGrath, Robby Findler, Ronald
Garcia, Ryan Culpepper, Ryan Kramer, Sam Tobin-Hochstadt, Shu-Hung You,
Sorawee Porncharoenwase, Spencer Florence, Stephen Chang, and Vincent
St-Amour

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