Fixed Racket v5.2.1 Installers

Dear Racketeers,

We have just released a DrRacket version 5.2.1 that starts fine today.  The fixed version has replaced the 5.2.1 installers.  This version and the original 5.2.1 differ only in this one fix.

Racket v5.2.1

Racket version 5.2.1 is now available from

http://racket-lang.org/

Release Highlights:

• Performance improvements include the use of epoll()/kqueue() instead of select() for the Racket thread scheduler, cross-module inlining of small functions, and the use of SSE instead of x87 for JIT-compiled floating-point operations on platforms where SSE is always available (including x86_64 platforms). A related change is the interning of literal numbers, strings, byte strings, characters, and regexps that appear in code and syntax objects.
• DrRacket uses a set of composable ray-traced icons available from the new images library collection.
• Typed Racket's typecheck-fail form allows macro creators to customize the error messages that Typed Racket produces. This is especially useful when creating pattern matching macros.
• The performance of Redex's matcher has been substantially improved; depending on the model you should see improvements between 2x and 50x in the time it takes to reduce terms.
• Plots look nicer and are more correct at very small and very large scales. New features include customizable dual axis ticks and transforms (e.g., log axes, date and currency ticks, axis interval collapse and stretch), stacked histograms, and 3D vector fields. The legacy fit function and libfit have been removed.
• The 2htdp/universe library's big-bang form supports an experimental game pad key handler.
• The db library now supports nested transactions and PostgreSQL arrays. Bugs involving MySQL authentication and memory corruption in the SQLite bindings have been fixed.
• The Macro Stepper tool in DrRacket no longer executes a program after expanding it.
• In the DMdA teaching languages, infinite recursive signatures ("streams", for example) with no intervening mixed are now supported, and the signatures of record definitions without fields now have generators for use with property.
• MysterX's ActiveX support is deprecated and will be removed in the next release. MysterX's core COM functionality will become deprecated in the next release, but COM functionality will be supported for the foreseeable future as a compatibility layer over a forthcoming ffi/com library.

Racket v5.2

Racket version 5.2 is now available from

http://racket-lang.org/

Release Highlights:

• DrRacket comes with an experimental, on-line check syntax tool, although this new tool is disabled default. See below for more information.
• The new db library offers a high-level, functional interface to popular relational database systems, including PostgreSQL, MySQL, and SQLite, as well as other systems via ODBC.
• A new XREPL collection provides convenient commands for a plain racket REPL. It is particularly convenient for people who prefer console-based work and alternative editors. See also the new chapter on command-line tools and other editors at the end of the Racket Guide.
• The plot collection has been reimplemented in Racket. It now offers PDF output, log axes, histograms, and more. Some code that uses plot will still work, and some will need light porting. The plot/compat module offers expedient backward compatibility.
• DrRacket uses more conventional key bindings: C-t creates a new tab, C-w closes the current one, and C-r runs the definitions. On Mac OS X, the Command key is used. See “Defining Custom Shortcuts” in the DrRacket manual for an example that uses the old key bindings.
• The new raco link command registers a directory as a collection, which allows the collection directory to reside outside the “collects” tree and without changing the PLTCOLLECTS environment variable.
• Typed Racket:
  • Typed Racket provides static performance debugging support to show which code gets optimized and point out code that does not. Use the “Performance Report” button in DrRacket.
  • More intuitive types in printouts in the REPL and in error messages. Use :query-result-type to explore types, or :print-type for a full printout.
  • Typed Racket now supports defining function with optional arguments using the same syntax as Racket.
• Redex now supports specifying (and testing and automatically typesetting) judgment forms including type systems and SOS-style operational semantics.
• Fixed several GUI problems, including problems on Ubuntu 11.10 (GTK+ 3) and 64-bit Mac OS X.
• Internal-definition expansion has changed to use let* semantics for sequences that contain no back references. This change removes a performance penalty for using internal definitions instead of let in common cases, and it only changes the meaning of programs that capture continuations in internal definitions. Internal definitions are now considered preferable in style to let.
• Support for begin-for-syntax has been generalized; modules may now define and export both value bindings and syntax bindings (macros) at phase 1 and higher.

  Due to a bug, phase 1 syntax (or higher) is not available in DrRacket's #lang-based REPL. A simple workaround is to disable debugging in DrRacket (see “no debugging” radio button in detailed language dialog).

Additional Items:

• The racket/gui library (and Slideshow) provides more support for multiple-screen displays.
• DrRacket remembers whether an opened file used LF or CRLF line endings, and will continue using the same. When creating a new file, a preference determines how it is saved.
• net/url can now follow HTTP redirections.
• The LNCS and JFP class files are no longer distributed with Racket. Instead, they are downloaded on demand.
• The Algol language implementation is now available as a plain language using #lang algol60.
• The Racket-to-C compiler (as accessed via raco ctool or mzc) has been removed; Racket's JIT has long provided better performance, and the FFI provides better access to C libraries.
• Contracts can be applied to exports with the new contract-out form within provide, instead of a separate provide/contract form. (The new contract-out form is implemented as a new kind of “provide pre-transformer”.)
• The date* structure type is an extension of date with nanosecond and time-zone-name fields.
• New looping constructs: for/sum and for/product.
• Direct calls to keyword-accepting functions are now optimized to eliminate the overhead of keywords. In addition, the compiler detects and logs warnings for keyword-argument mismatches.
• The libfit interface is available from plot/deprecated/fit, and will be removed in the near future.
• The Unix installer has been re-done, and it is now more robust.
• The built-in reader and printer support for Honu is removed. (This functionality is re-implemented in Racket.)

On-line Check Syntax:

DrRacket now provides an on-line version of the syntax check tool, which means that syntax checking runs automatically while you continue to edit a program. With this tool enabled, its annotations (e.g., binding arrows) and actions (e.g., the renaming refactoring and direct documentation links) are almost always available.

We have noticed that on-line syntax checking renders DrRacket unstable on occasion, perhaps because it relies on relatively new support for parallelism. Occurrences of the problem are rare, but they are not rare enough, which is why we have disabled the tool by default. At the same time, current users of the tool find it so valuable that we felt it should be included in the release. We expect to track down the remaining problems and enable the tool by default in near-future release.

To enable on-line syntax checking (for #lang-based programs only), click on the red dot in the bottom right of DrRacket's window. To turn it off, click there again.

Racket v5.1.3

Racket version 5.1.3 is now available from

  http://racket-lang.org/

This is a bugfix release, resolving the DrRacket issue with the contour view. In addition, two tex files with problematic licensing were removed.

Racket v5.1.2

Racket version 5.1.2 is now available from

  http://racket-lang.org/

• The download page includes 64-bit installers for Mac OS X, Windows, and two Debian flavors. Racket now supports OS X Lion.
• Racket now includes a new racket/place library to support parallelism, complementing racket/future. Racket's parallel build process is now based on places instead of multiple OS processes.
  Places support share-nothing parallelism and message-passing communication. Compared to futures, places are heavyweight, but they have a simpler performance model.
• The syntax-certificate system has been replaced by a syntax-taint system. Both certificates and taints were designed to protect otherwise inaccessible bindings from abuse when they appear in macro expansions. Taints are simpler and lighter, and the switch closes known holes in the certificate system. Macros that are not implemented with syntax-rules or define-syntax-rule, however, must explicitly use syntax-protect to protect their expansions from abuse.
• The net/url library supports HTTPS connections, but beware that by default all sites are accepted (equivalent to ignoring a browser's warnings about untrusted certificates).
• Error messages in the student languages use a simplified vocabulary and consistent phrasings. If you maintain curriculum material or teachpacks then please consider updating. See the “Error Message Composition Guidelines” section in the documentation for details.
• Typed Racket: almost all core Racket data structures and operations are now accessible in Typed Racket (most of this work is due to prolific contributor Eric Dobson). The performance of the typechecker has been significantly improved.
• The scriblib/bibtex library supports BibTeX-formatted citation databases in Scribble documents. BibTeX can be tricky to parse, so please report failed entries as bug reports.
• The for forms now support an #:unless clause, and a nonnegative integer can be used as a sequence. The new compose1 function creates single-valued composition functions. The racket/function library now provides identity, thunk, and thunk*.
• The license has been clarified: we now use LGPLv2.1 uniformly. (The license file used to specify LGPLv2, contrary to the download pages.)

Racket v5.1.1

Racket version 5.1.1 is now available from

  http://racket-lang.org/

• The new racket/stream library provides stream-first, stream-rest, a lazy stream-cons, and so on. Streams are a subtype of sequences, so they work in for forms. Some sequence generators, such as in-range, now produce streams. A racket/sequence library replaces the old racket/stream library.
• The new racket/syntax library contains facilities useful for writing macros. The new syntax/srcloc and syntax/location libraries provide support for manipulating source locations.
• The racket/gui library now supports multi-column list boxes and scrolling panels.
• The new ffi/file library is useful for writing foreign library bindings that cooperate with Racket's security guard mechanism.
• Generators from the racket/generator library can now have formal arguments that are used when the generator is fired up.
• Single-precision floating-point support is now enabled by default. Single-precision floats print differently from their default double-precision counterparts, new primitives convert between the two precisions, and new reader syntax supports single-precision literals.
• JIT improvements include a small change to aid x86 branch prediction on function-call returns, which can speed up some programs significantly.
• Typed Racket:
  • The numeric tower has been entirely overhauled. TR programs can now use more precise types than before, and check more numeric properties, such as sign or range properties.
  • Fixnum optimizations have been improved and should apply more broadly.
  • The performance of the typechecker has been improved. In particular, dispatch on large union types should typecheck much faster than before.
• The Stepper can now step through Lazy Racket programs.
• The racket/future library includes fsemaphore values, the future primitive no longer freezes futures (so a future can spawn new futures), and future log messages are more informative.
• PLaneT development links are now version-specific.
• The 2htdp/image library now includes overlay/align, underlay/align, overlay/align/offset and underlay/align/offset.
• The network protocol for universes in 2htdp/universe has changed, so that v5.1.1 is incompatible with earlier versions.
• The "DrScheme" application (which simply ran DrRacket in the last few releases) has been removed. The "MrEd" GUI executables for Windows and Mac OS X have also been removed, although the "mred" console executable remains for Unix and Mac OS X to support old scripts.

Racket v5.1

Racket version 5.1 is now available from

  http://racket-lang.org/

The most significant change in version 5.1 is a rewrite of the GUI library. Unix/X users will see the biggest difference with this change, because DrRacket and all Racket GUI programs now take on the desktop theme for menus, buttons, and other GUI widgets.

In the long run, Racket GUI programs on all platforms will improve as a result of the library rewrite. In the short run, beware that this first release of a new library will inevitably include a new set of bugs.

Version 5.1 changes in more detail:

• The racket/draw library—which implements the drawing half the GUI toolkit—can be used independent of the racket/gui/base library and without a graphics display (e.g., without an X11 connection).
  The new library has one small incompatibility with the old GUI toolbox: 'xor drawing is no longer supported. The new library has many additional features: rotation and general affine transformations, PDF and SVG drawing contexts, gradients, and alpha-channel bitmaps.
• The GRacket executable is no longer strictly necessary for running GUI programs, because the racket/gui/base library can be used from Racket. To the degree that a platform distinguishes GUI and console applications, however, the GRacket executable still offers some additional GUI-specific functionality (e.g., single-instance support).
  The new racket/gui/base library includes small incompatibilities with the old GUI toolbox: the send-event, current-ps-afm-file-paths, and current-ps-cmap-file-paths functions have been removed. The racket/gui/base library re-exports racket/draw, so it includes the same drawing functionality as before (except for 'xor drawing).
• The new racket/snip library can be used independently of racket/gui/base to work with graphical editor content (e.g., images in student programs). Like racket/draw, the racket/snip library is re-exported by racket/gui/base.
• The Web Server includes a backwards incompatible change that prevents X-expressions and lists of bytes from being directly returned from servlets. This change will increase performance for those types of responses and allow easier experimentation with response types. Please see "collects/web-server/compat/0/README" in the installation to learn about porting your servlets forward. Don't worry. It's easy.
• The new raco demodularize tool collapses a module's dependencies into a single module comprising the whole program. This transformation currently provides no performance improvement, but is the basis for cross-module optimization and dead-code elimination tools to come. The transformation is currently useful for static analysis of whole Racket programs.
• The picturing-programs teachpack, formerly installed via PLaneT, is now bundled with the standard distribution. Use the teachpack with (require picturing-programs) instead of (require installed-teachpacks/picturing-programs). The old PLaneT-based installation procedure still works, but it now merely installs a stub that invokes the bundled version.
• Slideshow picts, racket/draw bitmaps, and images created with 2htdp/image can now be used directly in Scribble documents. More generally, the new file/convertible protocol enables any value that is convertible to a PNG and/or PDF stream to be used as an image in a Scribble document.
• The Same game sports a new look and an improved scoring system. (The current known high score is 12,429; can you beat that?)

Racket v5.0.2

Racket version 5.0.2 is now available from

  http://racket-lang.org/

• Typed Racket's optimizer is now turned on by default; error messages have been simplified and clarified.
• Contracts: contracts on mutable containers allow functions or other higher order values, and contracts are checked when updating or dereferencing the containers. The new contracts are slower than the old ones, so the old check-once functionality is still available.
  A new dependent function contract combinator, ->i, properly assigns blame for contracts that violate themselves and the generated wrappers are more efficient than ->d. (Although it does more checking so your contracts may be faster or slower).
  See the docs for box/c, hash/c, vector/c, vectorof and ->i for more details.
• The when, unless, cond, case, and match forms (in racket/base and derived languages) now allow immediate internal definitions.
• Web server: the formlets library provides more HTML form elements; make-xexpr-response supports a preamble for DTD declarations; serve/servlet supports stateless servlets.
• New WebSocket implementation, see net/websocket for details.
• The new data collection contains implementations of several data structures, including growable vectors and order-based dictionaries.
• racket/match is now significantly faster.
• The Racket documentations are built in parallel by default.
• The stepper is now compatible with programs using the Universe teachpack.
• 2htdp/image: pinholes are now supported in the library (if you don't use pinhole primitives you will not see them); a number of new triangle functions added; supports conversion of images to color lists and back. Also, cropping has been improved for scenes; see the documentation section on the nitty-gritty of pixels for details.
• Signatures have been moved to ASL, BSL, BSL+, ISL, and ISL+ (HtDP teaching languages) no longer support checked signatures.
• Student languages: one-armed check-error in all levels; ASL is extended with hash operations, and define-datatype.
• DMdA languages: Checking for parametric signatures is now eager. This catches errors earlier, but retains the asymptotic complexity properties; signatures for record types now have generators; list-of and any signatures are now provided.

Racket v5.0.1

Racket version 5.0.1 is now available from

  http://racket-lang.org/

• Datalog is a lightweight deductive database system with Racket integration. It is now available in the datalog collection and with #lang datalog.
• Racklog provides Prolog-style logic programming in Racket, adapted from Dorai Sitaram's Schelog package. It is available in the racklog collection and now as #lang racklog.
• By default make install and raco setup compile collections in parallel on all available processors. (Use raco setup -j 1 to disable, if necessary.)
• Changes (as part of 5.0) in the racket language compared to the scheme language: constructor-style printing, a struct alternative to define-struct that fits more naturally with match and constructor-style printing, bytecode-dependency management via SHA-1 hashes instead of just timestamps (where the openssl/sha1 library provides the SHA-1 hash function), a reorganization of scheme/foreign into ffi/unsafe and associated libraries, and new printing functions eprintf and displayln. Also, a generator from racket/generator is required to have the form (generator () body ...), which supports a planned extension to let a generator accept arguments.
• Changes to the racket language (since 5.0): internal-definition positions allow mixing expressions with definitions, full continuations can escape past a continuation barrier, custodians can attempt to terminate subprocesses and subprocess groups (see current-subprocess-custodian-mode, subprocess-group-enabled), the JIT supports additional unboxing flonum operations and unsafe variants, ffi/unsafe provides an asychronous-call mechanism to deal with foreign threads, a new "." modifier for format string directives (e.g., "~.s" and "~.a") limits the respective output to (error-print-width) characters.
• The core type system of Typed Racket has been substantially revised. In particular, Typed Racket can now follow significantly more sophisticated reasoning about the relationships between predicates. Additionally, Typed Racket now allows variable arity types in more places, allowing programmers to specify variable-arity lists.
• We are working on an optimizing version of Typed Racket that takes advantage of type information for certain classes of programs. This project is a work in progress. For those interested, see the documentation for #:optimized.
• The web-server/formlets library adds a formlet* form that allows dynamic formlet construction, as opposed to formlet which requires syntactic Xexprs and static formlets. Several new library formlets are added.
• The syntax/parse library has new support for matching literals at different phases using the #:phase argument for literals and literal sets.
• RackUnit now includes a GUI test runner as rackunit/gui.
• The 2htdp/image library now includes flip-vertical and flip-horizontal operations that mirror images (vertically and horizontally).

Racket

PLT is happy to announce the release of Racket, available from

  http://racket-lang.org/

With Racket, you can script command shells and web servers; you can quickly prototype animations and complex GUIs; regexps and threads are here to serve you. To organize your systems, you can mix and match classes, modules or components. Best of all, you start without writing down types. If you later wish to turn your script into a program, equip your Racket modules with explicit type declarations as you wish. And Racket doesn't just come as a typed variant; you can also write your modules in a purely functional and lazy dialect.

Racket comes in so many flavors because Racket is much more than a standard scripting language or a plain programming language. Racket supports language extensibility to an unequaled degree. A Racket programmer knows that making up a new language is as easy as writing a new library.

To help you start quickly, Racket includes batteries in all shapes and sizes, most importantly, extensive documentation and all kinds of libraries.

Racket occupies a unique position between research and practice. It inherits many major ideas from language research, among them type safety (when the type system says that x is a number, then at runtime it always is a number) and memory safety (when some memory is reclaimed by the garbage collector it is impossible to still have a reference to it). At the same time, user demand governs rigid adherence to purely theoretical principles.

Racket, formerly PLT Scheme, is a product of over 15 years of development. Although Racket starts with a mature software base and an established user community, its new name reflects our view that this is just the beginning of Racket's evolution.

PLT Scheme v4.2.5

PLT Scheme version 4.2.5 is now available from

  http://plt-scheme.org/

• PLT now supports multi-core parallelism via futures. Futures create tasks that run in parallel, as long as the tasks stay in the "fast path" of the runtime system. For more information, see the guide.
• Our unit testing framework, schemeunit, is now included in the distribution. A graphical test runner is available via schemeunit/gui.
• The support languages for the "Programming Languages: Application and Interpretation" textbook by Shriram Krishnamurthi are now part of PLT Scheme. In addition the PLAI GC language comes with a random mutator generator (to help test collectors) and an improved heap visualizer.
• New Russian and Ukranian translations, thanks to Sergey Semerikov.
• A number of improvements to Redex's typesetting facilities.
• Typed Scheme users can now automatically generate predicates from types with define-predicate. Typed code can be inserted in untyped modules by requiring with-type from typed/scheme.
• The scheme/class library now provides contract combinators for classes (class/c) and objects (object/c). See the Reference and Guide for details. Also, a backwards-compatible object-contract version of object/c has replaced the old object-contract combinator.
• Writing new kinds of contracts is now easier with keyword-based constructors (make-contract and make-flat-contract), a simpler set of structure properties (prop:contract and prop:flat-contract), and the introduction of blame objects for tracking contract metadata.
• The Scheme-implemented bytecode reader fails less often. This is used by "mzc --decompile". The Scheme-implemented bytecode writer uses the compact bytecode format and fails less often. This may be used in the future for Scheme-implement bytecode processors.
• The language dialog now suggests using "#lang" more strongly as the default language. DrScheme no longer uses the term `Module language'.

PLT Scheme v4.2.4

PLT Scheme version 4.2.4 is now available from

  http://plt-scheme.org/

• 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 safety.
• 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 iteration.
• 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.

PLT Scheme v4.2.3

PLT Scheme version 4.2.3 is now available from

  http://plt-scheme.org/

• The unit test framework for the teaching languages provides check-member-of and check-range for checking "random functions", i.e., "functions" that may produce several different results for one and the same argument.
• Added a new image library, 2htdp/image. Significant changes from htdp/image:
  • copying and pasting does not introduce jaggies
  • equal? comparisons are more efficient
  • added rotation & scaling
  • got rid of pinholes (new overlay, beside, above functions based on bounding boxes)
• The scheme/vector library provides common vector operations (also reprovided by scheme).
• The scheme/promise library provides several new kinds of promises with alternatives execution strategies.
• New port-reading utilities: in-port, port->list, file->list.
• A new require-macro, path-up, for requiring a file that is higher in the directory tree.

PLT Scheme v4.2.2

PLT Scheme version 4.2.2 is now available from

  http://plt-scheme.org/

• 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.

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.

PLT Scheme v4.2

PLT Scheme version 4.2 is now available from

  http://plt-scheme.org/

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 expression.
• New in scheme/base: hash-has-key?, hash-ref!, in-sequences, in-cycle. New in scheme: count, make-list (from scheme/list), const (from scheme/function).
• 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 downloads.] Feedback Welcome.

PLT Scheme v4.1.5

PLT Scheme version 4.1.5 is now available from

  http://plt-scheme.org/

• Web Server:
  • new URL-based dispatching library web-server/dispatch,
  • customizable continuation serialization policies for the stateless web language web-server/stuffers,
  • abstraction of serve/servlet to build simpler dispatchers web-server/servlet-env,
  • HTTP Digest authentication support web-server/http/digest-auth,
  • built-in cookie support in web-server/http/cookie and web-server/http/cookie-parse,
  • highlighting and pretty-printing of errors in Xexpr constructions,
  • load control dispatcher for limit concurrent sessions web-server/dispatchers/limit.
• Scribble:
  • Literate programming is now available using the new scribble/lp language.
  • A new at-exp language makes it convenient to use the scribble reader's @-expressions for general code.
  • The scribble/text preprocessor language has been extended to deal with indentation and other formatting issues.
  • The "scribble" command-line tool accepts a --pdf flag to render PDFs (via pdflatex).
• DrScheme now provides feedback when PLaneT downloads and installs new packages.
• Units & Contracts:
  • Elements of unit signatures can now be associated with contracts via the contracted signature form.
  • A contract combinator for units, unit/c, has been added.
  • The new with-contract form provides a nestable submodule contract boundary, protecting a group of definitions from the surrounding code with contracts.
  • The define/contract form has been reworked and new define forms have been added: define-struct/contract and define-unit/contract.
• Language levels and teachpacks from the DeinProgramm project for the German textbook "Die Macht der Abstraktion" by Herbert Klaeren and Michael Sperber have been added.
• Misc:
  • Typed Scheme now comes with several more pre-wrapped libraries, found in the typed collection.
  • The xml and html collections are now contracted.
  • Binding parsing in net/cgi now interacts with net/uri-codec's configuration parameters.
  • DrScheme captures logging output.
  • Check syntax: it is now possible to tack arrows crossing the currently selected text.
  • New bitwise-bit-field function.
• The usual pile of bugfixes. (Notable: scheme/package works, deflate compression fixed, DrScheme language dialog issue resolved, match fixes, Windows networking, and much more.)

[Note that mirror sites can take a while to catch up with the new downloads.] Feedback Welcome.

PLT Scheme version 4.1.4 is now available from

  http://plt-scheme.org/

• New libraries include `scheme/package' (for nestable static modules) and `ffi/objc' (support for Objective-C).
• New teaching support includes a "universe.ss" teachpack for connecting "worlds" over a network.
• Redex now supports automatic test-case generation. Specify a predicate that should hold of your reduction system, and Redex will attempt to falsify it. See 'redex-check' in the manual for more details.
• Improvements to the run-time system include better and more reliable memory-limit tracking, function contracts that preserve tail recursion in many cases, native debugging backtraces on x86_64, and performance improvements.
• Improved libraries include enhancements to `scheme/sandbox', better handling of zero-sized matches by `regexp-split' and friends, an `equal<%>' interface for specifying equality on class instances (and more general support for attaching properties to interfaces), equality (via `equal<%>') for image objects, and refinements to `scheme/foreign' to support atomic operations and function-pointer conversions.

[Note that mirror sites can take a while to catch up with the new downloads.] Feedback Welcome.

PLT Scheme v4.1.3

PLT Scheme version 4.1.3 is now available from

  http://plt-scheme.org/

This is a bug-fix release. Notable changes:

• Web Server:
  • Documentation rewritten to separate servlet APIs and server extension APIs
  • HTTPS supported on the "plt-web-server" command-line with "--ssl" option
  • Stateless servlets supported in default configuration through 'stateless interface-version
  • `web-server/servlet-env' supports top-level servlets through #:servlet-path
  • Servlets are served from anywhere in the htdocs directory by default
  • A template system based on the Scribble syntax has been added, see web-server/templates in the documentation
  And many other internal modifications to make extension easier!

[Note that mirror sites can take a while to catch up with the new downloads.] Feedback Welcome.

PLT Scheme version 4.1.2 is now available from

  http://plt-scheme.org/

This is a bug-fix release. [Note that mirror sites can take a while to catch up with the new downloads.] Feedback Welcome.