[Racket announcement] Racket v6.12

From: Vincent St-Amour (stamourv at eecs.northwestern.edu)
Date: Fri Jan 26 18:08:33 EST 2018		 
Racket version 6.12 is now available from

    http://racket-lang.org/

* Changed the way some unsafe operations are exposed via `ffi/unsafe`
  libraries to help smooth a future transition to a new runtime system.

* The `syntax-parse` form supports unwinding side-effects when it
  backtracks, both explicitly with `~undo` patterns and implicitly
  with the built-in managed state (using `syntax-parse-state-ref`,
  etc).

* The `db` library supports SCRAM-SHA-256 authentication for backends
  running PostgreSQL 10 or later. Client support for SCRAM and other
  SASL mechanisms is provided by the new `sasl` library.

* The `lazy-require-syntax` form supports lazy loading of macro
  transformers. Note that the macros must obey certain implementation
  constraints (see the `lazy-require-syntax` documentation).

* Typed Racket no longer enforces types like (U String (Boxof String))
  with the any/c contract. This fixes a type soundness issue, but may
  affect performance. Please submit a bug report if you find a program
  that runs significantly slower on v6.12 than earlier versions.

* Typed Racket's type instantiation (`inst`) uses Any for omitted type
  arguments, allowing APIs to add additional type variables to functions
  without breaking existing programs.

* `for/fold` users can customize the final result of a loop's computation
  using the `#:result` keyword.

* The `--deps` option to `raco test` tests the packages the argument
  packages depends on, in addition to testing the packages themselves.
  For example, `raco test -p --deps pkg1 pkg2` tests all files from
  `pkg1`, `pkg2`, and all of their dependencies.

The following people contributed to this release:
Alexander Shopov, Alexis King, Andrew Gwozdziewycz, Andrew Kent, Ben
Greenman, Chung-chieh Shan, Conor Finegan, Daniel Feltey, Daniel
Mendler, Eric Dobson, Gabriel Ebner, Greg Cooper, Greg Hendershott,
Gustavo Massaccesi, Huma Zafar, Jack Firth, James Bornholt, Jay
McCarthy, John Clements, Kimball Germane, Leif Andersen, Matias
Eyzaguirre, Matthew Butterick, Matthew Flatt, Matthias Felleisen,
Michael Ballantyne, Mike Sperber, Milo Turner, Robby Findler, Rommel
Martinez, Ryan Culpepper, Sam Tobin-Hochstadt, Shu-Hung You, Soulaïmane
Sahmi, Spencer Florence, Stephen De Gabrielle, Vincent St-Amour, Wesley
Kerfoot, and William G Hatch.

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