$Id$

Changes between 3.0 and 4.0:
----------------------------

  * New in 3.99.8 prerelease:
    + Maintenance release with minor bugfixes.

  * New in 3.99.7 prerelease:
    + Last known garbage collector bug was fixed.

  * New in 3.99.6 prerelease:
    + Many portability checks added to the configure script.
    + Fix for an installation bug that prevented extension loading.
    + BeOS dynamic plugin support.

  * New in 3.99.5 prerelease:
    + R4RS compliance fixes (r4rstest.scm successful passes):
      - Allow for empty (begin) and (cond) statements.
      - Fixed scope of named let variables.
      - (eqv? 1 1.0) now properly returns #f.
    + Mac OS X compilation fixes.
    + Fixed the detection of environ on Solaris.

  * New in 3.99.4 prerelease:
    + Proper plugin support under Win32 and HP-UX.
    + Compilation fixes.
    + Minor bugs fixed.

  * New in 3.99.3 prerelease:
    + Minor bugs fixed.

  * New in 3.99.2 prerelease:
    + Ported to HP-UX.
    + Ported to Windows (both Cygwin and Mingw32) except the plugin system.
    + More bugs fixed.

  * New in 3.99.1 prerelease:
    + Ported to Mac OS X.
    + Added proper checks for the libraries (libgdbm, X11, Motif, ...).
    + Added a ChangeLog file.
    + libelf is no longer an absolute requirement, though it is still
      strongly recommended.

  * New in 3.99.0 prerelease:
    + libelk, a shared library containing all the Elk scheme interpreter
      features.
    + Properly builds with GCC 3.
    + 64 bits clean.
    + Uses autoconf, automake and libtool for greater portability and a
      simpler build and installation process.
    + Support for dynamically loadable plugins. Previous versions used the
      system's linker to build shared objects at runtime.
    + Massive bugfixing.
    + Dump support was removed because it was too platform-specific and
      could not be thoroughly tested. I may enable it again in the future.

Changes between 2.2 and 3.0:
----------------------------

General:

  * A new C/C++ Programmer's Manual for Elk is now available
    (60+ pages with many examples).  See doc/README (item `cprog')
    and doc/cprog.

  * The documentation has been prepared for translation to HTML
    using the (Elk-based) `unroff' package.

  * Elk now uses a new Scheme object representation (a `struct' rather
    than an `unsigned long') to make it work on 64-bit architectures
    and to allow for larger heaps, a wider range of fixnums, and more
    first-class Scheme types.

  * As a consequence, the `pointer_constant_high_bits' are gone, as
    is util/pchb.c.

  * Elk has been ported to and tested on these new platforms (config
    files are included in the distribution):

      DEC/Alpha, OSF/1
      HP 9000, HP-UX 10.0
      i386/486, BSDI BSD/OS
      i386/486, Linux
      IBM PowerPC, AIX 4.1

  * A number of config files for obsolete platforms have been removed
    from the distribution; config files for platforms where Elk 3.0
    could not be tested are in config/untested.  util/sgihack.c is gone.

  * Extension initialization and finalization functions now begin
    with `elk_init_' rather than just `init_' to avoid name conflicts.

  * The directory `contrib' has been removed from the distribution,
    as most of the contributions either were no longer maintained
    or have been made an official part of the distribution.
    contrib/eval-string is now available as lib/misc/elk-eval.c.

  * Site/platform-specific information such as the various X11 `load
    libraries', machine name, operating system name, as well as the
    Elk version number are now available as Scheme variables in
    scm/siteinfo.scm.  The file is created automatically and can be
    loaded via `(require 'siteinfo)'.

  * Most of the improvements in scm/debug-new.scm have been merged
    into the baseline debug.scm and the former has been removed.
    The inspector now starts at the correct frame when called after
    an error.

  * examples/CC/class.c is a simple Elk extension demonstrating
    encapsulation of a C++ class in a Scheme type.

  * The file README has been renamed ROADMAP; RELEASE is now README.

Interpreter kernel:

  * Many bugs have been fixed, and the code has been made `64-bit clean'.

  * New functions for application writers to read/set the `error tag'
    displayed in error messages and the application name (Get_Error_Tag,
    Set_Error_Tag, Set_App_Name).

  * When dynamically loading objects, the C++ static constructors are
    now called _before_ all extension initializers.  Ditto for C++
    destructors and extension finalizers.

  * New function for application/extension writers to load a file
    whose name is given as a C string (Load_File).
  * Load_Source_Port has been made `official' and may be used from
    outside the interpreter.

  * New functions for application/extension writers to convert
    Scheme numbers to C unsigned int/long: Get_Unsigned,
    Get_Unsigned_Long, Get_Exact_Unsigned, Get_Exact_Unsigned_Long.
    New function Get_Exact_Long.

  * The `round' primitive now rounds to even for numbers halfway
    between two integers.

  * The reader doesn't impose a limit on the length of strings and
    symbols any longer.

  * The dynamic loading implementations now use the environment
    variable TMPDIR if present.

  * `dump' now works under SGI Irix 5.x.

  * New constants ELK_MINOR and ELK_MAJOR for application/extension
    writers.

  * Symbols containing special characters now print correctly when
    output with `write'.

  * Various optimizations in the interpreter's inner loop to compensate
    for the performance loss caused by the struct-based object
    representation on some platforms.

Extensions:

  * The X11 extensions now work with X11 Release 6, Sun OpenWindows 3.x,
    and Sun Motif.

  * Extension-specific include files (unix.h, xlib.h, xt.h) are now
    installed in a subdirectory $install_dir/include/extensions
    for use by applications.

  * The object files for Athena or Motif widgets are now loaded
    by means of `require'.

  * New POSIX-style regular expression extension (see doc/regexp and
    examples/regexp).

  * The file hunk.c has been removed from lib/misc, as it no longer
    serves any purpose.

  * Several bugs have been fixed in the UNIX and X11 extensions.

Changes between 2.1 and 2.2:
----------------------------

General:

  * Elk ported to new platforms: SGI Irix 5.1, HP-UX 9.0

  * All Scheme files now end with the suffix `.scm'
  * Introduced new symbols in the config files to be used by the
    UNIX extension
  * Reorganized the include files.  Split external declarations
    into `private' (intern.h) and `public' (extern.h) declarations
    to be used by extensions

  * It's no longer necessary to specify multiple destination
    directories in the site file (only install_dir; subdirectories
    are created automatically)
  * `init_objects' is gone from the site file, see INSTALL for a
    new, simpler way to link extensions or an application with Elk
    statically
  * New directory $install_dir/lib is created with files module.o,
    standalone.o and shell scripts linkscheme, makedl, and ldflags
    (see INSTALL)

  * Elk can now be used by applications that must have their own
    main() function.  See INSTALL for details.

Interpreter kernel:

  * New primitives to allow blocking of signals from within Scheme
    code: disable-interrupts, enable-interrupts
  * Changed Disable_Interrupts and Enable_Interrupts macros to
    allow nesting and to handle signals used by extensions
    (specifically by the new UNIX extension)
  * Extended representation of continuations to carry current
    interrupt nesting level and restore it when being called
  * (Re-)enable interrupts in toplevel on error
  * Added default signal handlers for SIGPIPE and SIGHUP to clean
    up temporary files

  * New primitive: `features'
  * `require' now appends .scm to feature name to obtain file name
    (if no file name has been specified and if the feature name
    doesn't have a suffix yet)
  * Features elk:dump and elk:load-object are provided by the
    interpreter if dump and dynamic loading are supported

  * Implemented Register_Onfork() and Call_Onfork() to provide
    `fork handlers' (used, for instance, by the UNIX extension)
  * Added fork handlers to the dynamic loading implementations to
    create links for the temporary files

  * Added a close function to I/O ports to allow for pipe-based ports
  * New primitive: char-ready?

  * Added a check to the code that restarts a dumped interpreter
    to detect that the start address of the stack has been moved
    with respect to the original invocation (this happens between
    Sun-4c and Sun-4m architectures, for instance)

  * Modified math.c to implement the distinction between exact and
    inexact numbers as required by the language definition
  * New primitives: exact->inexact, inexact->exact
  * The number prefixes #e and #i are now supported
  * Floating point numbers are no longer automatically reduced to
    integers; new conversion function Make_Flonum(double) in
    addition to Make_Reduced_Flonum(double)
  * Added new conversion functions to cleanly distinguish between
    C ints and longs:  Get_Long(Object), Make_Long(long),
    Make_Unsigned_Long(unsigned long), and functions to convert
    bignums from/to C longs
  * New conversion functions for exact integers:
    Get_Exact_Integer(Object) and Get_Exact_Long(Object)

  * Removed the unique `void' type; #v is now converted into the empty
    symbol by the reader; void? remains for compatibility

  * Implemented reader table for #-syntax
  * New function Define_Reader() to allow extensions to register
    their own read syntaxes (used by the new bitstring extension)
  * Exported parts of the reader to simplify writing new reader
    functions in extensions

  * New functions/macros to convert Scheme strings and/or symbols
    into C strings (to be used by extension writers): Get_String,
    Get_Strsym, Get_String_Stack, Get_Strsym_Stack; see src/cstring.c
  * Now obsolete: Declare_C_Strings, Dispose_C_Strings, Make_C_String

  * Bug fixes:
      o  fixed a few bugs in the implementation of continuations and
         tail call optimization and in the generational, incremental
         garbage collector
      o  there was a bug in the interaction between the garbage
         collector and `dump'
      o  identified additional critical sections to be protected
         from delivery of signals
      o  initscheme.scm wasn't resolved against the load-path
      o  quasiquotation now also works for vectors (kudos to
         Tor Lillqvist for suggesting a simple fix)
      o  a bug in src/load-ld.c could cause the first static variable
         in a dynamically loaded .o file to not be zeroed

Extensions:

  * New UNIX extension; see doc/unix for the reference manual and
    examples/unix for a few demonstration programs

  * New record extension; see doc/record for the reference manual.
    The `struct' extension is now obsolete
    
  * New arbitrary-length bitstring extension; see doc/bitstring
    for the manual

Changes between 2.0 and 2.1:
----------------------------

General:

  * New configuration files for the 386/486-PC running 386BSD and
    DOS/DJGPP, for Suns running Solaris 2.1 (SunOS 5.1, and for
    the Convex C230 running ConvexOS.
  * Reorganized the config files and the site file to allow for
    configuration of the generational, incremental garbage collector
  * Introduced several new symbols in the config files to simplify
    installation on several systems
  * Added new targets to all Makefiles to allow `cross-localization'
    of the source tree (see comments in DOS section in MACHINES)

Interpreter kernel:

  * Added a generational, incremental garbage collector
  * New primitives: garbage-collect-status, collect-incremental
  * Reorganized the source files to accommodate the new garbage
    collector and to separate garbage collector specific code
    from code common to both garbage collectors

  * Empty list no longer counts as false; added primitive
    `empty-list-is-false-for-backward-compatibility'

  * Changed delimiter character in load-path argument of -p option
    from comma to colon
  * Initialize load-path from ELK_LOADPATH environment variable
    (if present)

  * Added argument to -v option to control which messages to print
    (linker command, init/finit functions)
  * It's no longer considered an error if an object file contains
    no initializers
        
  * Completely rewritten implementations of `dump' for ELF (SysVR4,
    Solaris 2.x), ECOFF (Ultrix, Irix), and HP9000 a.out formats;
    the HP version now correctly handles shared libraries
  * Added support for dynamic loading under SysVR4 and Solaris 2.x
    (see comments in MACHINES)
  * Added code to read symbol table of object files on the Convex

  * Bug fixes:
      o  dynamic-wind was completely broken; fixed it
      o  fixed a bug in the code that checks for the stack growing
         direction (caused dumped images to crash on startup)
      o  fixed a bug in the equal? predicate (could enter an
         infinite loop when applied to environments)
  * Fixed a number of portability problems, among them:
      o  added O_BINARY flag to open() calls and "b" mode to fopen()
         calls where necessary
      o  added support for the many different ways to purge a file
         pointer and tty file descriptor (src/read.c, src/print.c)

  * Integrated the functionality of the `libutil.a' library from
    older releases into the interpreter kernel (conversion of
    symbols and lists of symbols to bit masks and vice versa;
    routines to manage a pool of weak pointers to objects, used
    mainly by the Elk X extensions

Extensions:

  * Removed libutil.a (lib/util/*); moved the code into the
    interpreter kernel (src/terminate.c; src/symbol.c); removed
    libutil.a from the default load-libraries
  * Renamed lib/misc/c++.[co] to lib/misc/newhandler.[co] (c++.c isn't
    a valid filename under DOS)
  * Added finit function to lib/misc/monitor.c to switch off
    monitoring and write mon.out on exit

Elk/X:

  * The X extensions are no longer pre-linked against the required
    X libraries (by means of ld -r); resolving against system libs
    now always takes place at load time
  * make-gcontext and copy-gcontext now can be called with a drawable
    (i.e. pixmap or window)
  * New primitives: alloc-color alloc-named-color
  * Removed window-unique-id primitive
  * Fixed a few bugs in the Xt extension (editres now works with
    Scheme programs); removed an artificial limitation
  * Defined a GC visit function for widgets that visits each widget's
    parents and the children of composite widgets
  * Added support for Motif gadgets

Changes between 1.5 and 2.0:
----------------------------

General:
    
  * The build and install process has been improved significantly (see
    file INSTALL)
  * Added a new directory "config" that holds the system-specific
    configuration files and the site-file
  * Added a build shell script and a unified Makefile to all
    directories; "build" creates the ``real'' Makefiles containing
    system- and site-specific details during the make process
  * Added install, lint, clean, and distclean targets to all
    Makefiles
  * Placed files that are needed during runtime (dynamically loadable
    object files, Scheme files, the interpreter itself) into separate
    directories; added "make install" to put files there

  * Simplified porting Elk to new systems (assembly language support
    and a stack-extending version of "alloca" are no longer required)
  * Tested on several new systems (IBM RS/6000, HP9000/700, SGI,
    Sony; see the file MACHINES)

  * Placed new files CONTRIBUTORS, MIGRATE, and TODO into the toplevel
    directory of the distribution
  * Added a directory "util" that contains tools to simplify porting
    Elk to new environments and other utilities that are useful on
    some systems
  * Added a directory "scripts" that holds the shell scripts used
    to link instances of the interpreter and extensions.
  * Removed "stk" directory with test programs (no longer needed)

  * Added ANSI C prototypes and C++ "extern C" to all include files

Interpreter kernel:

  * Placed include files into a separate directory (include)
  * Reorganized the source files (separate source files for different
    a.out formats and different dynamic loading mechanisms)
  * Changed the way new Scheme objects are allocated to support the
    generational garbage collector (not yet present in Elk)
  * Rewrote the code implementing continuations to support full
    call/cc on all machines
  * Fixed tail recursion optimization
  * Added support for POSIX signals (as alternative to BSD reliable
    signals)
  * Removed several artificial limitations (such as max. number of
    before-GC and after-GC functions and statically GC-linked objects)
  * Removed code that depended on max. number of open files per process
  * Added bi-directional ports (input-output-ports); new primitive:
    open-input-output-port
  * New primitive: port-line-number
  * Reader now prints line number on syntax error
  * Max. length of a pathname is now determined correctly (using the
    POSIX incantations if applicable)
  * Added code to support dynamic loading under HP-UX (src/load-shl.c)
  * Added code to call extension finalization functions and C++
    destructors on termination
  * Fixed and improved the code to call extension initialization
    functions and C++ constructors on startup or when loading
    extensions
  * Improved the mechanism to suppress initialization of statically
    linked extensions on startup ("dont_init_if_name" in config/site)
  * Can use ANSI "atexit" as alternative to redefining "exit"
  * Added option -p to specify load path
  * Scheme file "initscheme" is now loaded before the toplevel is
    loaded
  * Changed "rand" to use rand() if random() isn't there
  * re-entrant-continuations? primitive is no longer needed (returns
    always #t now)
  * Added a general mechanism to register termination functions for
    individual objects (e.g. to close files on GC); see src/terminate.c
  * linkscheme shell script improved; added code to support the
    stupid AIX linker
  * Fixed numerous things that caused lint or "gcc -ansi" to complain
  * Changed the dynamic loading, "dump", and a.out symbol table reading
    code in numerous places to make it work on new systems and to make
    it more readable and maintainable

Extensions:

  * Combined lib/util/symbol.o and lib/util/objects.o into new library
    libutil.a; put this library into the default "load-libraries"
  * Moved lib/util/string.c and lib/util/string.h into the interpreter
  * Moved files from lib directory into new subdirectory "misc"
  * Added POSIX sysconf stuff to unix.c to determine max. number of
    open files per process

Elk/X:

  * Made the code mostly "lint clean" and "gcc -ansi clean"
  * Fixed bogus variable definitions in xlib.h and xt.h
  * Xlib: added support for client-message event
  * Xt: added code to avoid a bug in Motif 1.1.4
  * Xt: added optional "mask" argument to context-add-input
  * Removed site-dependent information from scm/xwidgets (file is
    now created from scm/xwidgets.src during the build process)
  * Renamed widget .d files that were longer than 14 characters;
    added ALIASES file for each widget set containing mappings from
    real widget names to short names

Documentation:

  * Added sub-directory "paper" containing a draft version of a
    paper about Elk

User-contributed extensions:

  * A foreign function interface, an Elk Shell, and a vector extension
    have been contributed by J. P. Lewis (contrib/zelk).

Changes between 1.4 and 1.5:
----------------------------

General:
  * Added a "contrib" directory for user-contributed extensions
    that I have not fully tested and/or integrated into Elk
  * Renamed ORIGIN to COPYRIGHT

Interpreter kernel:
  * Added support for the Amiga, A/UX and System V Release 4
    (ELF a.out format)
  * Added special load-library for MIPS (-lc_G0)
  * Extension-interface: replaced Val() by Var_Set()/Var_Get()
  * Modified load, autoload, and require so that multiple .o-files
    can be loaded simultaneously
  * Added -1+ as a synonym for 1-
  * Bug fixes:
      o  fixed a GC-related bug
      o  fixed a bug that occurred when allocating a very large heap
      o  fixed a bug in case-insensitive string comparison
      o  fixed a bug in macro "when"
      o  changed and clarified semantics of print-depth/print-length
  * IEEE 1178/R^4RS compatibility:
      o  replaced close-port by close-input-port and close-output-port
      o  added primitives caaaar .. cddddr
      o  added peek-char primitive
      o  added -i option for case-insensitive operation
  * Removed -bc option
  * Removed CBREAK-hack in read-char

Elk/X:
  * Fixed several GC-related bugs (objects belonging to Xlib/Xt are
    no longer terminated by garbage collector when unreferenced)
  * Fixed a bug in the interface to the Grip widget
  * Modified code to load widgets to make use of new capability to
    load multiple .o-files

Documentation:
  * Interpreter kernel:  documented new functions, clarified
    some sections
  * Xlib/Xt:  documented X-related behavior of garbage collector,
    pointed out GC-related pitfalls

Changes between 1.3 and 1.4:
----------------------------

Interpreter kernel:
  * Support for the NeXT machines added
  * New primitive list? provided
  * Two bugs in the tail recursion code fixed
  * -v option to trace /bin/ld-calls
  * man-page written

Elk/X:
  * Tested under X11R5
  * X11R3 and earlier versions are no longer supported
  * The HP-widget code has been removed from the distribution

  * New Xlib-primitives:  install-colormap  uninstall-colormap
    list-installed-colormaps  xlib-release-5-or-later?

  * Xt interface now supports actions and accelerator tables
  * Bug in set-context-fallback-resources! fixed
  * New Xt-functions:  widget-name  widget-translate-coordinates
    application-initialize  context-add-action  install-accelerators
    install-all-accelerators  xt-release-5-or-later?

  * Support for new widget classes: menubutton panner porthole repeater
    simplemenu sme smebsb smeline stripchart tree
  * vpaned renamed to paned

  * Example programs have been moved into a new examples directory
    with sub-directories for Scheme, Xlib, Xaw, Motif

  * New Xaw example programs that demonstrate the new widget classes,
    accelerators, actions, etc.

Other extensions:
  * Interface to the GNU gdbm-library