ChangeLog.txt

The contents of this file are subject to the GNU General Public License
(GPL) Version 2 or later (the "License"); you may not use this file except
in compliance with the License. You may obtain a copy of the License at
http://www.gnu.org/copyleft/gpl.html

Software distributed under the License is distributed on an "AS IS" basis,
without warranty of any kind, either expressed or implied. See the License
for the specific language governing rights and limitations under the
License.

This file was originally developed as part of the software suite that
supports the book "The Elements of Computing Systems" by Nisan and Schocken,
MIT Press 2005. If you modify the contents of this file, please document and
mark your changes clearly, for the benefit of others.


2.5
===

General
-------

Added: Completely redesigned web site. The site has a new look & feel and 
       contains more information in less text.

Added: Lectures for all projects to the web site.

Compiler
--------

Added: Error when returning a value from a void function or returning with
       no value from a non-void function.

Added: Error when the program flow could reach past the last statement of a
       subroutine (without being obstructed by a 'return' statement).

Added: Warning when unreachable statements are encountered.

Added: All compiler messages now have a uniform look which also includes the
       current class and subroutine name (in addition to the description and
       line number).

Added: Most of the compiler code has been reorganized so that upon an error
       parsing always continues (upon all semantic errors parsing continues
       straight away; upon most syntax errors a reasonable correction is
       guessed and parsing continues straight away as well; parsing continues
       from a near point otherwise) -  this way the vast majority of errors
       are reported in one program run.

Added: Upon a compilation failure on a file, the compilation process does not
       stop - compilation of the next file is attempted.
       Subroutine calls are only cross-referenced with their signatures
       if the file containing the subroutine definition was successfully
       compiled (otherwise no cross-referencing is done, as if the erroneous
       file was not given as an argument to the compiler). This is done
       to avoid massive errors upon problems with the subroutine (and not with
       calls).

Added: Upon a compilation error, the generated file is deleted. The file is
       still generated upon a "link"-style error (error when cross-referencing
       subroutine signatures and calls).

Added: Clearer. far more indicative error messages on many common Jack
       programming mistakes.

Fixed: Line numbers in the source code reported in errors/warnings are now
       always correct (the line number of the next token was previously
       reported in most cases, and in the rest of the cases yet even a higher
       number than that of the next token was reported).

Added: Error if a source file contains any code beyond the closing } of the
       class definition (previously this was silently ignored)

Added: When run with no parameters, a about/usage message is printed.
       This message is consistent with the about/usage dialog boxes of the
       graphic applications of the software suite.

Fixed: An error when declaring two subroutines (of any kinds) of the same name
       in the same class is now always issued when needed.


2.0
===

General
-------

Fixed: .bat/.sh files used to launch the programs now work also when activated
       from a prompt from a different directory. These files also now work
       correctly when there's a file name with spaces in the classpath
       (like when the JRE on windows was installed into "Program Files").

Fixed: In all simulator/emulators, the while command now behaves as it should.
       Previously the body of the while was ignored which resulted in a
       busy wait for nothing. So far this command has only been used in
       Memory.tst and this was overlooked there because the memory polling
       worked after a while even though the "eval" command was skipped but
       this created a very heavy CPU load.

Fixed: The "official" version number is now the same as the one displayed
       by all programs.

Added: All zip archives are now compressed with the "best" compression,
       making all of them considerably smaller.

Added: Added FAQ and errata sections to the web site.

Projects
--------

Fixed: Numerous file name errors in scripts (case errors, suffix errors),
       most of which caused tests not to compile or not to work on
       unix platforms.

Fixed: Some project files on the site were different in their zipped version
       than in their non-zipped version. All such discrepancies have been
       synchronized and are being kept synchronized with a set of scripts.

Added: For better ease-of-use, project 1 tst and cmp files do not contain
       any hexadecimal values anymore.

Added: Project 3 Bit test now catches many more bad implementations.

Added: Project 3 Register/RAM* tests have been systematically revamped to
       catch many more bad implementations - most are now around a 1000
       lines in length.

Fixed: Project 5 CPU.cmp would fail on a good chip that was implemented
       differently. Fixed by using wildcards for outM when writeM is false.

Added: Alternative, not recommended, ess thorough implementations for some
       project 5 tests which do not require the use of specific built-in chips.

Fixed: Bat destructor was not called in Project 11 PongGame.jack.

Added: Project 12 StringTest now also tests a zero-capacity string.

Fixed: Project 12 StringTest now tests setInt regardless of whether the
       implementation of Output.printInt calls it. Also, just to be on the
       safe side, appendChar is tested also in the remote case of a
       student-written compiler which doesn't use appendChar for string
       literals (highly unlikely - how would the length of a string be
       incremented?).

Assembler
---------

Fixed: Spaces are now correctly ignored in the comp part of a C-instruction.

Fixed: An error is reported within the program if the loaded comparison
       file contains non-0/1 characters (previously an exception was thrown).

Fixed: An error is reported within the program if a line in the loaded
       comparison file is not of length 16 (previously the file was loaded
       and the lines were compared numerically so the comparison would even
       succeed in certain cases).

Added: The version number is now displayed in a fashion consistent with the
       rest of the software suite.

Hardware Simulator:
-------------------

Added: Detailed documentation for the Chip API in the Readme.txt file of the
       open source distribution.

Added: Support for wildcards in compare files of the Hardware Simulator.
       This was added to allow fixing of the CPU.cmp test file.

Fixed: No check was performed that a gate definition was closed (}). This
       means that no errors were issued when a /* comment was not closed or
       after loading a partial or incomplete HDL file.

Fixed: The binary input component now appears in the correct location with
       the correct number of active bits. Also, double-clicking on another
       input pin while the binary input component resulted in the wrong input
       being updated - this is now fixed with a new behaviour which has the
       same feel as the decimal input: clicking on another input pin now closes
       a visible binary input component while double clicking on another
       input pin now opens the binary input component for that pin. Also enter
       and escape presses now correspond to pressing the ok/cancel buttons
       to complete the correct feel for this component.

Added: Clearer error when a script attempts to directly access a built-in
       chip that's not loaded (like the when using the project 5 scripts
       accessing PC[] or ARegister[] when these have not been used).

CPU Emulator:
-------------

Fixed: Negative values may now be stored in the A register as long as no
       attempt to dereference them or to jump to them is made.

VM Emulator:
------------

Added: Support for built-in implementation of VM functions (similar to
       built-in gates). The API enabling this (the VMCode API) is meticulously
       documented in the Readme.txt file of the open source distribution.
       Via this API, a built-in implementation for all Jack OS
       classes was added - they can work in any combination of built-in/*.vm
       classes. This yields a noticeable speedup in running Jack-OS-based
       VM applications, especially in graphics drawing (no need to make
       the space invaders look like squares anymore :) ) - it is advisable
       to add Sys.wait calls to code that runs too fast now (try running
       Pong now - it's like running the XT version of Digger on a Pentium).
       How it works: Load a directory which doesn't contain a *.vm
       implementation for the Jack OS classes. A dialog will pop up to
       confirm the usage of built-in implementations - click 'Yes'.
       Now run everything normally - when encountering a call to a function
       in a class with no *.vm implementation and if that function has a
       built-in implementation, it will be invoked. If data flow animation
       is on, the changing of heap/screen memory by built-in functions will
       be animated. The built-in implementation of Sys.error and Sys.halt
       now offer the side-effect of a pop-up window with information
       regarding the reason for the program halt.

Fixed: Incorrect size of local segment and of stack when returning from a
       function called when more values than its arguments were on the stack.

Fixed: Incorrect detection (both false positive and false negatives) of
       encountering a 'function' statement in the middle of a function
       definition.

Fixed: Memory leak when restarting a program from inside a function
       (stackFrames vector not cleared).

Fixed: Error regarding static segment if Sys.init accidentally contains a
       return statement (and not enters an endless loop).

Added: Added an error when loading a program consisting of multiple files
       when there is no implementation of Sys.init.

Added: Now support c-style /* */ comments (because the programs on pages 138
       and 140 accidentally contained such comments).

Operating System:
-----------------

Fixed: The cursor is now displayed when expecting input, as described in the
       book.

Fixed: Backspace now wraps from the beginning of a line to the previous,
       providing a more natural behaviour when the user inputs a string
       to the Keyboard.readLine function.

Compiler:
---------

Added: Error when calling a method of the current class from within a function
       implicitly, as if for the "this" object.

Added: Error when calling a function or constructor of a known (passed to the
       compiler for compilation, regardless of the compilation order) class
       as a method (both from the same class for the "this" object implicitly,
       and for non-this objects of a known class explicitly).

Added: Error when calling a method of a known class as a function/
       constructor.

Added: Error when calling a non-existent function/method/constructor of
       a known class.

Added: Error when declaring two subroutines (of any kinds) of the same name
       in the same class.

Added: Error when calling a subroutine of a known class with a different
       number of arguments than the declared number of arguments.


1.0
===

First public release - released with the book.