[plt-scheme] PLT Scheme v204 available

PLT Scheme v204 is now available from 

   http://download.plt-scheme.org/ 

Overview
--------

  Help Desk reverted
  openssl library added
  channels & CML primitives added
  SRFIs integrated
  match.ss rewritten
  error display improved

Details
-------

- Help Desk reverted [rationale below]

  We have once again reorganized Help Desk. Specifically, we
  have resurrected and improved PLT's browser and use it to
  provide helpful information. 

- openssl library added

  openssl bindings for PLT Scheme (`ssl-connect',
  `ssl-listen', etc.) are available as an easy-to-install
  add-on from:

     http://www.plt-scheme.org/software/openssl/ 

- channels & CML primitives added

  PLT Scheme's concurrency primitives now include support
  for synchronous channels and programmer-defined
  sychronization abstractions a la Reppy's Concurrent ML.

- SRFIs integrated 

  The release includes all SRFI implementations from
  Schematics: 1, 2, 4, 5, 6, 7, 8, 9, 11, 18, 19, 23, 25,
  26, 28, 29, 30, and 31. Use

    (require (lib "N.ss" "srfi")) 

  to import SRFI N into a module. 

- match.ss rewritten

  Bruce Hauman's rewrite of the "match.ss" library removes
  many bugs and offers several improvements. Further
  improvements will appear in the next release.

- error display improved

  When a runtime error occurs and debugging is enabled,
  DrScheme draws red arrows on the program text indicating
  the stack at the time the error was raised. Each arrow
  points from the source location of one activation
  record (typically a procedure call) to the source location
  of the next activation record.

Why Help Desk has changed, again
--------------------------------

  In recent versions of PLT Scheme, Help Desk started an 
  "external" browser (such as Internet Explorer) for reading 
  and searching help content. Although external browsers provide 
  better HTML rendering than our own browser, the process of 
  managing an external browser is complex and fragile. In many 
  subtle ways, the use of an external web browser application 
  runs counter to Help Desk's purposes.	 Instead of continuing 
  to fight this obstacle, we have decided to spend our time
  improving our help-specific browser.

Enjoy!

-- Paul