v6.1 announcement text

pkgs/plt-services/meta/announcements/v6.1.txt

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+1407000198
+Racket 6.1
+
+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.