[PLT announcement] PLT Scheme v4.2

From: Eli Barzilay (eli at barzilay.org)
Date: Mon Jun 1 14:24:45 EDT 2009

PLT Scheme version 4.2 is now available from


Internally, this version includes a conversion from C++ to Scheme
for part of the GUI toolbox --- specifically, 25k lines of code
that implement the general text and pasteboard editor.  This
conversion is a start on a larger reimplementation of the GUI
toolbox.  Although we believe that this change will help make PLT
Scheme better in the long run, we must expect bugs in the short
term due to porting errors.  Users should therefore be aware of
the change, even though the new implementation is meant to behave
the same as previous versions.

* A new statistical profiler is now available; see the "profiler"
  manual for more information.  Currently, the profiler supports
  only textual output, but future plans include a GUI interface
  and DrScheme integration.

* The `world' teachpack is now deprecated.  Its replacement
  `universe' has a new interface that uses strings instead of
  symbols and characters.

* Web-server: Native continuations in the stateless servlet
  language support capturing continuations from untransformed
  contexts; soft state library for stateless servlets.

* DrScheme's Stepper can now jump to a selected program

* New in `scheme/base': `hash-has-key?', `hash-ref!',
  `in-sequences', `in-cycle'.  New in `scheme': `count',
  `make-list' (from `scheme/list'), `const' (from

* Some performance improvements, including faster start-up for small
  programs. The latter is a result of delaying module invocations at
  higher phases (compile time, meta-compile time, etc.) until
  compilation is demanded at the next lower phase; this on-demand
  instantiation is per-phase, as opposed to per-module within a phase.

[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://www.barzilay.org/                 Maze is Life!

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