[PLT announcement] PLT Scheme v4.2.1

From: Eli Barzilay (eli at barzilay.org)
Date: Thu Jul 30 08:06:45 EDT 2009

PLT Scheme version 4.2.1 is now available from


* This is the last release that includes ProfessorJ. As of the
  next release, Kathy Gray who created and maintained the
  Professor will move the code to planet and maintain only at a
  minimal level.

* Typed Scheme 2.0 extends the type system significantly, making
  it more expressive.  For example, predicates applied to
  selectors, such as (number? (car x)), are meaningful to the type

* Faster installation of Planet packages that trigger install of
  other Planet packages, because the documentation index is
  updated only once after a group of packages is installed.

* The `syntax/parse' library provides macro writers with an
  enhanced syntax pattern matcher that reports errors based on the
  patterns' declared classes of syntax.

* Identifier mappings following the v4 dictionary interface and
  naming conventions are available from the `syntax/id-table'

* Redex: added `define-relation' and generalized patterns that
  appear in "where" clauses to use the full Redex pattern matcher.
  (This is a backwards incompatible change, but one often
  requested; see the Redex release notes for details.)

* The Web Server's serializable closures are now available for
  other purposes through the web-server/lang/serial-lambda

* Teachpacks: small changes to universe portion of the
  "universe.ss" API, plus the addition of a form for launching
  many (communicating) worlds simultaneously.  Bug fixes
  concerning conversion to strings.

* It is now possible to create custom scribble readers with a
  command characters different than `@', see
  `make-at-reader/inside' and `make-at-reader'

* Note: this is likely to be the last release that includes a
  solaris distribution.  If you need these builds, or if you have
  access to a (Sparc) Solaris machine than can be used in PLT
  builds, then please let me know.

[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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