------------------------------------------------------------------------
Version 4.2.4				  [Thu Jan 28 12:02:01 EST 2010]

* separated 2htdp/universe from htdp/image
* 2htdp/universe contains some stupid hacks to improve performance 
  -- to be changed with Matthew's advice  
* error modified 
* added a bunch of primitives for JPR 
* fixed some other bugs 

------------------------------------------------------------------------
Version 4.2.3				  [Sun Nov 22 19:25:01 EST 2009]

* bug fixes in universe 
* 2htdp/image (first draft)

------------------------------------------------------------------------
Version 4.2.2				  [Sat Aug 29 15:44:41 EDT 2009]

* universe API: 
  -- added a (state Boolean) option for world and server programs 
  to display their actual state in a separate window 
  -- added a mechanism for displaying a final scene 
  when the world is about to come to an end 

------------------------------------------------------------------------
Version 4.2.1				  [Wed Jul 22 11:15:54 EDT 2009]

* universe API: added launch-many-worlds, fixed numerous small bugs
  concerning symbol and char elimination

------------------------------------------------------------------------
Version 4.2				  [Thu May 21 08:51:15 EDT 2009]

* the universe API has changed. It no longer uses chars or symbols
  for the callbacks but one-letter strings, except for arrow keys 
  and special events, which are arbitrarily long strings. 

------------------------------------------------------------------------
Version 4.1.5   			  [Sat Feb 14 20:12:23 EST 2009]

* the universe teachpack exports iworld, not world now

------------------------------------------------------------------------
Version 4.1.4				  [Sun Jan 18 21:18:34 EST 2009]

* introduces 2htdp/universe 
* small bug fixes in world.ss

------------------------------------------------------------------------
Version 4.1.3				  [Wed Nov 19 10:20:41 EST 2008]

tiny bug fixes 

------------------------------------------------------------------------
Version 4.1.2				  [Sat Oct 25 10:31:05 EDT 2008]

nothing new to report

------------------------------------------------------------------------
Version 4.1.1				  [Tue Sep 30 10:17:26 EDT 2008]

* world.ss: big-bang can now be re-run after the world has stopped

------------------------------------------------------------------------
Version 4.1				  [Sun Aug 10 12:56:58 EDT 2008]

* world docs include line to HtDP/2e Prologue 

------------------------------------------------------------------------
Version 4.0.1				  [Fri Jun 20 10:35:32 EDT 2008]

* world.ss: replaced 'end-of-world' with a hook called 'stop-when'

------------------------------------------------------------------------
VERSION 4.0				  [Thu May  8 11:03:30 EDT 2008]

* small bug fixes in world

* added matrix.ss (requires a write up)


------------------------------------------------------------------------
VERSION 371				  [Tue Aug  7 17:49:47 EDT 2007]

* changed world.ss so that it exports both add-line from image.ss and
  scene+image. 

------------------------------------------------------------------------
VERSION 370				  [Mon May  7 09:54:19 EDT 2007]

* Added testing.ss teachpack. 

* The world.ss teachpack now has a IMAGE capturing functionality, including
  animated GIFs. It also supports simple simulations now. 

* The world.ss and image.ss support real numbers for sizes and coordinates
  now. 

* The ProfessorJ wizard doesn't support templates for now. 

------------------------------------------------------------------------
VERSION 360				  [Tue Nov  7 12:45:48 EST 2006]

 * The world.ss teachpack has now callback hooks for mouse clicks. 

 * The image.ss teachpack now includes a star primitive. 

 * Fixed bugs in world.ss, graphing.ss, image.ss

------------------------------------------------------------------------
VERSION 351				  [Tue Jul 18 14:11:29 EDT 2006]

 * The libraries for ProfessorJ are now organized as four packages: 
   draw, idraw, geometry, and colors. 

 * Fixed small problems with master.ss and image.ss teachpacks and their
   docs. 

------------------------------------------------------------------------
VERSION 350				  [Fri Jun 16 20:37:38 EDT 2006]

 * The draw package (ProfJ) spawns a new Canvas per new Canvas. 
   The implementation of draw.ss has changed for that, though the visible
   interface should remain the same. 
   
 * The idraw package provides imperative versions of World and Canvas. 

 * Small bugs in world.ss and image.ss fixed. 

 * servlet.ss and servlet2.ss are still missing. Expect their arrival
   for 351. 

------------------------------------------------------------------------
VERSION 300				  [Mon Dec 12 15:59:02 EST 2005]

 * The world.ss teachpack has changed. It no longer supports 
   (update ... produce ...) but instead provides a function 
   on-redraw. 

 * servlet.ss and servlet2.ss are still missing. Expect their arrival
   for 301. 

------------------------------------------------------------------------
VERSION 299.200				  [Tue Aug  2 17:37:24 EDT 2005]

 * servlet.ss and servlet2.ss are still missing. Expect their arrival
   for 300. 

 * draw.ss in the HtDCH teachpack collection has radically changed. See
   the doc.txt file for the new arrangement. 

------------------------------------------------------------------------
VERSION 209				  [Fri Dec 17 10:19:52 EST 2004]

 * fixed small bugs in image.ss and world.ss concerning colors and the
   location of pinholes 

 * The interface of the draw teachpack (package) for ProfessorJ has
   changed. A World now supports draw and erase methods. The onTick and
   onKeyEvent methods call erase on the current world, create the next
   world, and then call draw on the new world. 

------------------------------------------------------------------------
VERSION 208p1

* fixed a bug in image.ss; find-image now returns the result
  relative to the pinhole. Misc image.ss docs improvements.

------------------------------------------------------------------------
VERSION 208				  [Fri Jul 30 10:07:21 EDT 2004]

* image.ss introduces images as algebraic values. Students can create basic
  images such as rectangles, circles, and they can compose them via an
  overlay function. There are also primitives for finding one picture in
  another one and so on. Testing with drawing is now feasible. 

* world.ss enriches image.ss with animation functions. Like draw.ss, it
  comes with big-bang, on-key-event, on-tick, end-of-time for creating a
  world, starting a clock, reacting to clock ticks and keystrokes, and
  ending time. It also comes with a mechanism for display movies. It does
  *not* yet provide primitives for dealing with mouse clicks.

  The performance problems from the TS! workshops have been eliminated. 

------------------------------------------------------------------------
VERSION 207  			          [Fri May 14 12:52:43 EDT 2004]

* draw.ss now comes with functional callbacks for maintaining a visual
  world: big-bang, on-key-event, on-tick, end-of-time 

* draw also comes now as a ProfessorJ implementation in the htdch 
  collects directory. This is an experimental teachpack. Docs are available
  via doc.txt. Experiences with students may change this teachpack
  significantly. 
 
------------------------------------------------------------------------
VERSION 203  			          [Thu Dec  5 09:10:40 EST 2002]

* added get-key-event to draw.ss 

------------------------------------------------------------------------
VERSION 201  			          [Wed Jul 24 22:44:19 EDT 2002]

* added servlet.ss and servlet2.ss 

* all exported functions are primitive operators or higher order primitives
  this improves error reporting behavior in the Beginner languages (before
  higher-order functions are introduced)

* removed: 
  pingp-play.ss   
  pingp.ss        
  protect-play.ss 
  rectangle.ss    
  these teachpacks aren't mentioned in htdp, and aren't used for any 
  of the additional exercises

------------------------------------------------------------------------
VERSION 200alpha1			  [Wed Nov 21 13:07:43 EST 2001]

* Robby converted to modules 

* Fixed bug in convert.ss 

------------------------------------------------------------------------
VERSION 103				  []

* modified draw.ss interface so that colors are symbols
  use 'red instead of RED 

------------------------------------------------------------------------
VERSION 102				  [Thu Jun 22 18:22:48 CDT 2000]

* Added "convert.ss" to teachpacks/htdp

* Fixed error messages for some arity tests

* Fixed documentation 

------------------------------------------------------------------------

VERSION 101				  [Tue Oct 26 22:28:38 CDT 1999]


* TERMINOLOGY: We decided to eliminate the terminology "teaching
  library", because it is easily confused with a plain library. As of
  release 101, we refer to one of these objects as a

    teachpack

* USAGE: Inside of DrScheme, the menu choice called "Language|Set
  library to..."  is now called "Language|Set teachpack to...".

* LOCATION of Files: The distributed teachpacks are found at

    $PLTHOME/teachpack/
    PLTHOME is the location of the PLT software

  The htdp subdirectory contains those files that matter to students who
  use HtDP. 

* CHANGES in individual teachpacks: The most important and most visible
  change in the teachpack support concerns

    hangman.ss 

  It now provides two GUI interfaces: (1) hangman for three-letter words
  and (2) hangman-list for words of arbitrary length. See the teachpack
  documentation for details. 

  The teachpack 

    master.ss

  now exports the procedure _master_, which is exactly like the procedure
  _repl_ in the old master-lib.ss library. 

  The corresponding exercises in HtDP have been rewritten and are posted
  on the HtDP Web site.

* REMINDER: The *purpose* of teachpacks is to supplement student programs
  with code that is beyond the teaching languages (Beginner, Intermediate,
  Advanced). For example, to enable students to play hangman, we supply a
  teachpack that 
    - implements the random choosing of a word 
    - maintains the state variable of how many guesses have gone wrong 
    - manages the GUI. 
  All these tasks are beyond students in the third week and/or impose
  nothing memorization of currently useless knowledge on students. 

  A teachpack is a signed unit that imports the interface:   

    plt:userspace^

  The exported names are added to the read-eval-print loop at the end of
  an EXECUTE step.

------------------------------------------------------------------------

Version 100

The plt:userspace^ signature does not contain the
graphics library. In order to use the graphics library in your
teachpacks, use a compound unit and link in graphics directly. For example:

  (require-library "graphics.ss" "graphics")
  
  (define-signature my-teachpack^ (four))
  
  (define my-teachpack
    (unit/sig my-teachpack^
      
      (import plt:userspace^ 
              graphics^)
      
      '...
      
      (define four 4)))
  
  (compound-unit/sig 
   (import [P : plt:userspace^])
   (link [G : graphics^ ((require-library "graphicr.ss" "graphics")
                         (P : mzlib:file^)
                         (P : mred^))]
         [TP : my-teachpack^ (my-teachpack P G)])
   (export (open TP)))

The graphics^ signature contains all of the primitives in the
graphic.ss library. Search for "graphics" in Help Desk for more
information on those primitives.
