[PLT announcement] PLT Scheme v4.2.2

From: Eli Barzilay (eli at barzilay.org)
Date: Sun Oct 4 16:16:17 EDT 2009

PLT Scheme version 4.2.2 is now available from


* DrScheme now, by default, compiles all of the files that are
  loaded when it runs a program and saves the compiled files in the
  filesystem.  This should lead to faster load times (not faster
  runtimes) since it avoids re-compiling files whose dependencies
  have not changed.

* New Scribble libraries and documentation make it easier to get
  started with Scribble, especially for uses other than PLT
  documentation.  DrScheme now has better indentation and syntax
  coloring support for Scribble languages (and generally all @-exp
  based languages).

* The new `syntax/keyword' library provides support for macros with
  keyword options.  A new quick start guide has been added to the
  documentation for the `syntax/parse' library.

* Added support for abstract contracts via the #:exists keywords.
  This is an experiment to add support for data hiding to the
  contract system.

* Added `in-producer': a sequence expression makes it easy to
  iterate over producer functions (e.g., `read').  A new
  `scheme/generator' library creates generators that can use a
  (parameterized) yield function.

* HtDP langs: several primitives now consume 0 and 1 arguments in
  ISL (and up), including `append', `+' and `*'.  In addition,
  `make-list' was added to the primitives.

* The API to Universe has a number of new constructs.  All Universe
  programs should run unchanged.  The most important change is the
  addition of `animate' as an alternative name for `run-simulation'.
  In addition, adding the clause `(state true)' to a world
  description now pretty-prints the state of the world into a
  separate canvas.

* A number of changes were made to the DeinProgramm / DMdA language
  levels: The `check-property' and `contract' forms were added,
  `define-record-procedures-parametric' has changed.  See the
  documentation for details.

* The test engine in the HtDP languages no longer warns programmers
  when the Definitions window has no tests.

* ProfessorJ (and related code) is no longer included in the PLT
  distributions.  It may re-appear in the future as a PLaneT package.

[Note that mirror sites can take a while to catch up with the new

Feedback Welcome,
          ((lambda (x) (x x)) (lambda (x) (x x)))          Eli Barzilay:
                    http://barzilay.org/                   Maze is Life!

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