This is Lua 4.1 (alpha).

* Changes from version 4.0 to 4.1 (alpha)
  ---------------------------------------
  Language:
  + support for weak tables.
  + user-defined types (= names for tags).
  + new library functions: time, tmpfile, unpack, require, loadfile, loadstring
  + position capture in strfind.
  + (f()) adjusts the values returned by f to a single result.
  + more general syntax for function definition (e.g., function a.x.y:f()...end)
  API:
  + new API functions: lua_newthread, lua_loadfile, lua_loadstring, ...
  Implementation:
  + support for external multi-threading and coroutines.
  + safe garbage-collector tag methods.
  + new, faster, register-based virtual machine.
  + precompiled bytecodes checked for integrity.
  + strings are fully aligned.
  + read('*l') can read lines with embedded zeros.

* Changes from version 3.2 to 4.0
  -------------------------------
  Language:
  + new "break" and "for" statements (both numerical and for tables).
  + uniform treatment of globals: globals are now stored in a Lua table.
  + improved error messages.
  + no more '$debug': full speed *and* full debug information.
  + new read form: read(N) for next N bytes.
  + general read patterns now deprecated.
    (still available with -DCOMPAT_READPATTERNS.)
  + all return values are passed as arguments for the last function
    (old semantics still available with -DLUA_COMPAT_ARGRET)
  + garbage collection tag methods for tables now deprecated.
  + there is now only one tag method for order.
  API:
  + New API: fully re-entrant, simpler, and more efficient.
  + New debug API.
  Implementation:
  + faster than ever: cleaner virtual machine and new hashing algorithm.
  + non-recursive garbage-collector algorithm.
  + reduced memory usage for programs with many strings.
  + improved treatment for memory allocation errors.
  + improved support for 16-bit machines (we hope).
  + code now compiles unmodified as both ANSI C and C++.
  + numbers in bases other than 10 are converted using strtoul.
  + new -f option in Lua to support #! scripts.
  + luac can now combine text and binaries.

* Changes from version 3.1 to 3.2
  -------------------------------
  + redirected all output in Lua's core to _ERRORMESSAGE and _ALERT.
  + increased limit on the number of constants and globals per function
    (from 2^16 to 2^24).
  + debugging info (lua_debug and hooks) moved into lua_state and new API
    functions provided to get and set this info.
  + new debug lib gives full debugging access within Lua.
  + new table functions "foreachi", "sort", "tinsert", "tremove", "getn".
  + new io functions "flush", "seek".

* Changes from version 3.0 to 3.1
  -------------------------------
  + NEW FEATURE: anonymous functions with closures (via "upvalues").
  + new syntax:
    - local variables in chunks.
    - better scope control with DO block END.
    - constructors can now be also written: { record-part; list-part }.
    - more general syntax for function calls and lvalues, e.g.:
      f(x).y=1
      o:f(x,y):g(z)
      f"string" is sugar for f("string")
  + strings may now contain arbitrary binary data (e.g., embedded zeros).
  + major code re-organization and clean-up; reduced module interdependecies.
  + no arbitrary limits on the total number of constants and globals.
  + support for multiple global contexts.
  + better syntax error messages.
  + new traversal functions "foreach" and "foreachvar".
  + the default for numbers is now double.
    changing it to use floats or longs is easy.
  + complete debug information stored in pre-compiled chunks.
  + sample interpreter now prompts user when run interactively, and also
    handles control-C interruptions gracefully.

* Changes from version 2.5 to 3.0
  -------------------------------
  + NEW CONCEPT: "tag methods".
    Tag methods replace fallbacks as the meta-mechanism for extending the
    semantics of Lua. Whereas fallbacks had a global nature, tag methods
    work on objects having the same tag (e.g., groups of tables).
    Existing code that uses fallbacks should work without change.
  + new, general syntax for constructors {[exp] = exp, ... }.
  + support for handling variable number of arguments in functions (varargs).
  + support for conditional compilation ($if ... $else ... $end).
  + cleaner semantics in API simplifies host code.
  + better support for writing libraries (auxlib.h).
  + better type checking and error messages in the standard library.
  + luac can now also undump.

* Changes from version 2.4 to 2.5
  -------------------------------
  + io and string libraries are now based on pattern matching;
    the old libraries are still available for compatibility
  + dofile and dostring can now return values (via return statement)
  + better support for 16- and 64-bit machines
  + expanded documentation, with more examples

* Changes from version 2.2 to 2.4
  -------------------------------
  + external compiler creates portable binary files that can be loaded faster
  + interface for debugging and profiling
  + new "getglobal" fallback
  + new functions for handling references to Lua objects
  + new functions in standard lib
  + only one copy of each string is stored
  + expanded documentation, with more examples

* Changes from version 2.1 to 2.2
  -------------------------------
  + functions now may be declared with any "lvalue" as a name
  + garbage collection of functions
  + support for pipes

* Changes from version 1.1 to 2.1
  -------------------------------
  + object-oriented support
  + fallbacks
  + simplified syntax for tables
  + many internal improvements

(end of HISTORY)
