meg4/docs/en/lua.md

Lua

If you want to use this language, then start your program with a #!lua line.

Example Program

#!lua

-- global variables
acounter = 123
anumber = 3.1415
anaddress = 0x0048C
astring = "something"
anarray = {}

-- Things to do on startup
function setup()
  -- local variables
  iamlocal = 234
end

-- Things to run for every frame, at 60 FPS
function loop()
  -- Lua style print
  print("I", "am", "running")
  -- Get MEG-4 style outputs
  printf("a counter %d, left shift %d\n", acounter, getkey(KEY_LSHIFT))
end

Further Info

Unlike the other languages, this isn't integral part of MEG-4, rather provided by a thrid party library. Due to that it does not (and cannot) have perfect integration (no debugger and no translated error messages for example). Its runner is bloated and much slower compared to the other languages, but it works, and you can use it.

The embedded version is Lua 5.4.7, with modifications. For security reasons it lacks concurrency, as well as module loading, file access, pipes, command execution. The coroutine, io and os modules and their functions aren't available (but the language features and all the other parts of the baselib are still there). Instead of these missing tables, it has the MEG-4 API, which can be used as in any other language (with some slight, minor differences for better integration).

If you're interested in this language then you can find more information in the Programming in Lua documentation.

API Differences

• [memsave] can accept either a MEG-4 memory address (integer) or a Lua table with integers (supposed to be a byte array).
• [memload] on call, a valid MEG-4 memory address must be passed, but then it returns a Lua table anyway. If you don't want to load to a specific MMIO area, then specify MEM_USER (0x30000) and just simply use the data in the returned Lua table.
• [memcpy] parameters can be two MEG-4 memory addresses as usual, or one of them can be a Lua table (just one, not both). You can use this function to copy data between MEG-4 memory and Lua (but [inb] and [outb] also works).
• [remap] only accepts a Lua table (with 256 integer values).
• [maze] instead of the last two parameters (numnpc and npc) one single Lua table (with each element being another table) can be used.
• [printf], [sprintf] and [trace] does not use MEG-4's [format string] rules, but Lua's (however these two are almost entirely identical).