PLT Scheme v4.2.1

PLT Scheme version 4.2.1 is now available from

  http://plt-scheme.org/

• 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 system.
• 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 library.
• 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 library.
• 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.