Racket 6.3 发布，更新如下：
Racket's macro expander uses a new representation of binding called "set of scopes". The new binding model provides a simpler explanation of how macros preserve binding, especially across module boundaries and in hygiene-bending expansions. The new expander is mostly compatible with existing Racket macros, but there are some incompatibilities. For the formally inclined, a research paper on this macro system will appear at POPL next year: http://www.cs.utah.edu/plt/scope-sets/
Racket's GUI library now uses Gtk+ 3 when available, instead of Gtk+ 2. Set the PLT_GTK2 environment variable to select Gtk+ 2.
Added a new Redex tutorial based on a week-long workshop in SLC.
Better syntax error checking for Redex patterns that do not use holes correctly.
The blueboxes are more agressive about finding names to look up in the docs, meaning they are useful much more often.
Submodules are now fully supported in Typed Racket. Previously, some uses of submodules would produce internal errors, making it hard to module+ test and module+ main effectively in Typed Racket. The switch to the set-of-scopes expander fixed these problems, and submodules are now happily at home in Typed Racket.
The typed/racket/unsafe library provides import and export forms that circumvent contract generation. This improves performance for typed-untyped interaction at the cost of safety and debuggability.
Typed Racket provides experimental support for units (from racket/unit).
The experimental define-new-subtype form allows overlaying finer distinctions between otherwise identical types, similar to Haskell's new type.
The Promise type constructor changes in a backwards-incompatible way to exclude promises created with promise/name.
The unstable-* packages are out of the main distribution. Most of their contents have been either merged with established Racket libraries or spun off as their own packages. This change is backwards compatible for packages that properly list their dependencies. Full details: http://blog.racket-lang.org/2015/10/retiring-unstable.html
edu: big-bang supports a display-mode clause so that world programs can take over the entire screen.
Racket源自著名的专家型语言PLT Scheme，同时又是Lisp语言的一个分支。它适用于从脚本Script到应用程序开发的任务执行工具，包括图形用户界面，Web服务器等。支持编译器的虚拟机，创建独立的可执行程序的工具，Racket Web服务器，具有丰富而全面的功能库，适用于初学者和专家编程。