[PLT announcement] PLT Scheme v4.2.4

From: Eli Barzilay (eli at barzilay.org)
Date: Thu Jan 28 21:32:33 EST 2010

PLT Scheme version 4.2.4 is now available from


* The `scheme/flonum' and `scheme/fixnum' libraries provide flonum-
  and fixnum-specific operations.  In the case of flonum-specific
  operations, the JIT compiler can recognize combinations of
  operations (including local bindings) and improve performance by
  "unboxing" intermediate results.

* The `scheme/unsafe/ops' library provides arithmetic and other
  operations that are implemented without dynamic checks.  Avoiding
  checks can sometimes improve performance, but at the expense of

* `2htdp/universe': We have severed the connection between universe
  and an image library and made a few other, minor changes.  Most
  programs will now have to change to require the `htdp/image'
  library explicitly.  For the full details, see the new Porting
  World Programs section of the documentation:

* The `2htdp/image' library continues to grow.  In this release, it
  is supported by `2htdp/universe', equality changed to be based on
  how the images are drawn, cropping and curves were added, and
  support for more kinds of pens were added.

* `htdp/world': The old world teachpack remains deprecated.  HtDP/2e
  exclusively uses the new 2htdp/universe library.  For backwards
  compatibility, the world teachpack will remain in the distribution
  until the coming summer.

* The `scheme/class' library now provides `this%', which refers to
  the class of the current object (i.e. `this').

* `scheme/generator' has convenient functions for infinite
  generators, and for converting a generator to a sequence for

* PLT Scheme's add-on directory can be customized by the
  $PLTADDONDIR environment variable or `--addon'/`-A' command-line
  flags.  This controls where downloaded Planet packages and their
  compiled Scribble documentation are installed.

* Additional extensions include: saving `errno' in foreign calls,
  much improved `sort' speed, normalized results from
  `procedure-arity', and more.

[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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