--******************************************************************************
--*                                                                            *
--*  File:        ExplicitGlobals.lua                   Revision:  1.0         *
--*                                                                            *
--*  Purpose:     requires global variables to be explicitly declared          *
--*                                                                            *
--*  Creation:    13.03.2002                   Last Modification:  04.04.2002  *
--*                                                                            *
--*  Platform:    IBM-compatible PC running Windows 98SE                       *
--*                                                                            *
--*  Environment: Lua 4.0, TkLua 4.0                                           *
--*                                                                            *
--*  Author:      Andreas Rozek           Phone:  ++49 (711) 6770682           *
--*               Kirschblütenweg 15      Fax:    -                            *
--*             D-70569 Stuttgart         EMail:  Andreas.Rozek@T-Online.De    *
--*               Germany                                                      *
--*                                                                            *
--*  URL:         http://www.Andreas-Rozek.de/                                 *
--*                                                                            *
--*  Copyright:   the software is published under the "GNU Lesser General Pub- *
--*               lic  License" (see "http://www.fsf.org/copyleft/lesser.html" *
--*               for additional information)                                  *
--*                                                                            *
--*  Comments:    (none)                                                       *
--*                                                                            *
--******************************************************************************

--**** do not execute this script more often than once ****

  if (type(global) == "function") then return nil; end;

--**** load any definitions required by this script ****

  if (type(import) ~= "function") then
    dofile("LibrarySupport.lua");  -- provides a simple library import mechanism
  end;

  import("BasicDefinitions");      -- provides basic definitions for Lua scripts

--**** maintain a list of declared globals ****

  local declaredGlobals = globals(); -- automatically "declare" existing globals
  for Key,Value in declaredGlobals do
    declaredGlobals[Key] = 1;       -- keep the "name" rather than the "content"
  end;

--******************************************************************************
--*                                                                            *
--* global                    registers the given name(s) for global variables *
--*                                                                            *
--******************************************************************************

  function global (...)
    local ArgCount = getn(arg);
    if (ArgCount == 1) and isList(arg[1]) then
      call(global,arg);
    else
      for i = 1,ArgCount do
        assert(                                     -- also rejects 'nil' values
          type(arg[i]) == "string",
          "invalid type of argument (expected \"string\", got \""..type(arg[i]).."\")"
        );

        %declaredGlobals[arg[i]] = 1;
      end;
    end;
  end;

--******************************************************************************
--*                                                                            *
--* getglobal                 replacement for the homonymous built-in function *
--*                                                                            *
--******************************************************************************

  local getglobal = function (Name)
    assert(
      type(Name) == "string",                       -- also rejects 'nil' values
      "invalid type of argument \"Name\" (expected \"string\", got \""..type(Name).."\")"
    );

  --**** check for a declaration of 'Name' ****

    assert(%declaredGlobals[Name],"undeclared global \""..encodedString(Name).."\"");

  --**** and then actually retrieve the given global ****

    return nil;              -- the predictable result "rawget(globals(), Name)"
  end;

--******************************************************************************
--*                                                                            *
--* setglobal                 replacement for the homonymous built-in function *
--*                                                                            *
--******************************************************************************

  local setglobal = function (Name, Value)
    assert(
      type(Name) == "string",                       -- also rejects 'nil' values
      "invalid type of argument \"Name\" (expected \"string\", got \""..type(Name).."\")"
    );

  --**** check for a declaration of 'Name' ****

    assert(%declaredGlobals[Name],"undeclared global \""..encodedString(Name).."\"");

  --**** and then actually set the given global ****

    rawset(globals(), Name, Value);
  end;

--******************************************************************************
--*                                                                            *
--*                                main program                                *
--*                                                                            *
--******************************************************************************

--**** install accessor functions for global variables ****

  settagmethod(tag(nil), "getglobal", getglobal);
  settagmethod(tag(nil), "setglobal", setglobal);