Getting started with LUA/pas2lua

[JernejL]

{$mode delphi} // fixes this

I had mode Delphi defined at the top of the unit. It didn't fix that.

it has to be defined prior the "unit xyz" part.

[Robert Kosek]

Oh, I'd have to go back and double check that, thanks for the tip. Though that's the least of my problems currently; I'm having trouble passing a function as an argument (Pointer style) that is making the program choke.

[jdarling]

Working with functions as parameters isn't near as easy as it sounds. You have to keep a reference to the function in the Lua Registry, and then you have to use that entry to actually call the function.

The following is a "simple" sample:[pascal]function lua_CallFunc(L : PLua_State) : Integer; cdecl;
var
n, callTimes, funcRef, c, pidx : Integer;
pArray : array of variant;
begin
n := lua_gettop(L); // Get the number of items on the stack
callTimes := lua_tointeger(L, 1); // Get the number of times to call the function
if lua_type(L, 2)=LUA_TFUNCTION then // Make sure we have a function
begin
lua_pushvalue(L, 2); // Make a copy to push to the registry
funcRef := luaL_ref(L, LUA_REGISTRYINDEX); // push to the registry and get the reference
try
SetLength(pArray, n-3); // Get the params that we are passing
for c := 3 to n do
pArray[c-3] := luatovariant(L, c);
for c := 1 to callTimes do
begin
lua_rawgeti(L, LUA_REGISTRYINDEX, funcRef); // Place the reference on the stack
for pidx := 0 to length(pArray)-1 do // place each param on the stack
luapushvariant(L, pArray[pidx]);
lua_call(L, length(pArray), LUA_MULRET); // Call the function
end;
finally
luaL_unref(L, LUA_REGISTRYINDEX, funcRef); // Release the reference to the function
end;
end;
lua_CallFunc := 0;
end;[/pascal]

The Lua "Prototype" for this would be:
function CallFunc(NumTimes, FuncPointer, ...)

Of course, for speed, when using a known function you should cache the function registry reference for re-use. Then release it when you no longer need it.

Hope that helps some, just typed it in looking at some working code. But, there may be problems

[Robert Kosek]

Uh, no, check the previous page. I cannot even register the functions... :?

Okay, this is silly. I found that TLua doesn't contain "RegisterMethod" so I had to use "LuaRegister" instead, but now, after changing a few things for compatibility I now get this when running the executable file:

C:\FPC\projects\luaexec>luaexec
An unhandled exception occurred at $1000C33A :
EAccessViolation : Access violation
  $1000C33A
  $00407067
  $004070CE
  $004013D2

I updated the Lazarus project though I am not using that directly, just using straight FPC instead. It might be my register function for the CRT "library" but I really don't know. You can get the whole project from here. What'd I do this time? :?

Also, I noticed numerous errors in my functions and the IFDEF clause the newer definition in the source is much better.

EDIT:

This is screwy. It's telling me that it doesn't want a pointer/address to the function, then I remove the @ symbol it immediately complains of too few arguments. What's going on!? This doesn't even raise an error in the LuaCRT unit, but in the main one it does. :?

Also, I noticed that registering the CRT library functions caused that access violation; I don't know how, why, or how to fix it though.

[Robert Kosek]

Okay, I tried this, and it raises the error that it has insufficient arguments.

[pascal]procedure RegisterCRT(L: PLua_State);
var
idx : Integer;
begin
lua_pushliteral(L, 'crt');
lua_newtable(L);
idx := lua_gettop(L);
LuaRegisterCustom(L, 'KeyPressed', lua_KeyPressed, idx);
LuaRegisterCustom(L, 'ReadKey', lua_ReadKey, idx);
LuaRegisterCustom(L, 'GetXY', lua_GetXY, idx);
LuaRegisterCustom(L, 'TextColor', lua_TextColor, idx);
LuaRegisterCustom(L, 'BackgroundColor', lua_BackgroundColor, idx);
LuaRegisterCustom(L, 'ClrScr', lua_ClrScr, idx);
LuaRegisterCustom(L, 'ClrEol', lua_ClrEol, idx);
LuaRegisterCustom(L, 'DelLine', lua_DelLine, idx);
LuaRegisterCustom(L, 'GotoXY', lua_GotoXY, idx);
LuaRegisterCustom(L, 'InsLine', lua_InsLine, idx);
LuaRegisterCustom(L, 'Window', lua_Window, idx);
// lua_settable(L,idx);
lua_settable(L, LUA_GLOBALSINDEX);
end;[/pascal]

But when I try this, it completely freaks out with the following error messages:[pascal]procedure RegisterCRT(L: PLua_State);
var
idx : Integer;
begin
lua_pushliteral(L, 'crt');
lua_newtable(L);
idx := lua_gettop(L);
LuaRegisterCustom(L, 'KeyPressed', @lua_KeyPressed, idx);
LuaRegisterCustom(L, 'ReadKey', @lua_ReadKey, idx);
LuaRegisterCustom(L, 'GetXY', @lua_GetXY, idx);
LuaRegisterCustom(L, 'TextColor', @lua_TextColor, idx);
LuaRegisterCustom(L, 'BackgroundColor', @lua_BackgroundColor, idx);
LuaRegisterCustom(L, 'ClrScr', @lua_ClrScr, idx);
LuaRegisterCustom(L, 'ClrEol', @lua_ClrEol, idx);
LuaRegisterCustom(L, 'DelLine', @lua_DelLine, idx);
LuaRegisterCustom(L, 'GotoXY', @lua_GotoXY, idx);
LuaRegisterCustom(L, 'InsLine', @lua_InsLine, idx);
LuaRegisterCustom(L, 'Window', @lua_Window, idx);
// lua_settable(L,idx);
lua_settable(L, LUA_GLOBALSINDEX);
end;[/pascal]

LuaCRT.pas&#40;76,68&#41; Error&#58; Incompatible type for arg no. 4&#58; Got "SmallInt", expected "<procedure>"
LuaCRT.pas&#40;77,68&#41; Error&#58; Incompatible type for arg no. 4&#58; Got "SmallInt", expected "<procedure>"
LuaCRT.pas&#40;78,68&#41; Error&#58; Incompatible type for arg no. 4&#58; Got "SmallInt", expected "<procedure>"
LuaCRT.pas&#40;79,68&#41; Error&#58; Incompatible type for arg no. 4&#58; Got "SmallInt", expected "<procedure>"
LuaCRT.pas&#40;80,68&#41; Error&#58; Incompatible type for arg no. 4&#58; Got "SmallInt", expected "<procedure>"
LuaCRT.pas&#40;81,68&#41; Error&#58; Incompatible type for arg no. 4&#58; Got "SmallInt", expected "<procedure>"
LuaCRT.pas&#40;82,68&#41; Error&#58; Incompatible type for arg no. 4&#58; Got "SmallInt", expected "<procedure>"
LuaCRT.pas&#40;83,68&#41; Error&#58; Incompatible type for arg no. 4&#58; Got "SmallInt", expected "<procedure>"
LuaCRT.pas&#40;84,68&#41; Error&#58; Incompatible type for arg no. 4&#58; Got "SmallInt", expected "<procedure>"
LuaCRT.pas&#40;85,68&#41; Error&#58; Incompatible type for arg no. 4&#58; Got "SmallInt", expected "<procedure>"
LuaCRT.pas&#40;86,68&#41; Error&#58; Incompatible type for arg no. 4&#58; Got "SmallInt", expected "<procedure>"
LuaCRT.pas&#40;233&#41; Fatal&#58; There were 11 errors compiling module, stopping
LuaCRT.pas&#40;5,50&#41; Fatal&#58; Compilation aborted

Should I try "function as lua_CFunction" or "lua_CFunction(function)"? This is a bit crazy. I hope this doesn't occur very frequently when messing with Lua initially. :?

[Sly]

What is the declaration of LuaRegisterCustom()?

[Robert Kosek]

Lua.pas

type
  lua_CFunction = function(L : Plua_State) : Integer; cdecl;

LuaRegisterCustom, LuaUtils.pas

procedure LuaRegisterCustom(L: PLua_State; TableIndex: Integer; const Name: PChar; F: lua_CFunction);
var
  Count: Integer;
  S: string;
begin
  LuaProcessTableName(L, Name, S, TableIndex, Count);
  LuaRawSetTableFunction(L, TableIndex, S, F);
  lua_pop(L, Count);
end;

All my functions are adhering to both call/definition correctly too. :? That's the strange part. I call the register function for the CRT functions I made, commenting out the search routine (I still cannot register it), and the instant they are registered (output isn't even started) that exception occurs and the application dies.

[jdarling]

Robert, you don't want to use the register methods from LuaUtils. Instead look at the register methods in my LuaWrapper and LuaObjects units.

Post up a zip of your source files and I'll adjust it to work. Then you can compare the two and see what I'm talking about.

[Robert Kosek]

I updated the Lazarus project though I am not using that directly, just using straight FPC instead. It might be my register function for the CRT "library" but I really don't know. You can get the whole project from here. What'd I do this time? :?

Also, I noticed numerous errors in my functions and the IFDEF clause the newer definition in the source is much better.

EDIT:

This is screwy. It's telling me that it doesn't want a pointer/address to the function, then I remove the @ symbol it immediately complains of too few arguments. What's going on!? This doesn't even raise an error in the LuaCRT unit, but in the main one it does. :?

Is there something wrong with those register methods? They were the only really simple way to register the functions to a table that I could find. The way you gave me before FPC couldn't find the needed function. :?

EDIT: You mean to try the RegisterMethod from LuaObject.pas? So, I should just use that instead I guess. Though, I honestly don't understand the duplicity and frequency of so many functions to try and do that same thing.

EDIT2: As in something like this to register my functions?[pascal]procedure RegisterCRT(L: PLua_State);
var
idx : Integer;
begin
lua_pushliteral(L, 'crt');
lua_newtable(L);
idx := lua_gettop(L);
RegisterMethod(L, 'KeyPressed', @lua_KeyPressed, idx);
RegisterMethod(L, 'ReadKey', @lua_ReadKey, idx);
RegisterMethod(L, 'GetXY', @lua_GetXY, idx);
RegisterMethod(L, 'TextColor', @lua_TextColor, idx);
RegisterMethod(L, 'BackgroundColor', @lua_BackgroundColor, idx);
RegisterMethod(L, 'ClrScr', @lua_ClrScr, idx);
RegisterMethod(L, 'ClrEol', @lua_ClrEol, idx);
RegisterMethod(L, 'DelLine', @lua_DelLine, idx);
RegisterMethod(L, 'GotoXY', @lua_GotoXY, idx);
RegisterMethod(L, 'InsLine', @lua_InsLine, idx);
RegisterMethod(L, 'Window', @lua_Window, idx);
// lua_settable(L,idx);
lua_settable(L, LUA_GLOBALSINDEX);
end;[/pascal]Attempting that immediately gave me this when attempting to compile:

LuaObject.pas&#40;462,49&#41; Error&#58; Incompatible type for arg no. 3&#58; Got "<address>", expected "<procedure>"
LuaObject.pas&#40;463,55&#41; Error&#58; Incompatible type for arg no. 3&#58; Got "<address>", expected "<procedure>"
LuaObject.pas&#40;464,46&#41; Error&#58; Incompatible type for arg no. 3&#58; Got "<address>", expected "<procedure>"
LuaObject.pas&#40;465,43&#41; Error&#58; Incompatible type for arg no. 3&#58; Got "<address>", expected "<procedure>"
LuaObject.pas&#40;466,46&#41; Error&#58; Incompatible type for arg no. 3&#58; Got "<address>", expected "<procedure>"
LuaObject.pas&#40;467,43&#41; Error&#58; Incompatible type for arg no. 3&#58; Got "<address>", expected "<procedure>"
LuaObject.pas&#40;484,49&#41; Error&#58; Incompatible type for arg no. 3&#58; Got "<address>", expected "<procedure>"
LuaObject.pas&#40;485,55&#41; Error&#58; Incompatible type for arg no. 3&#58; Got "<address>", expected "<procedure>"
LuaObject.pas&#40;487,43&#41; Error&#58; Incompatible type for arg no. 3&#58; Got "<address>", expected "<procedure>"
LuaObject.pas&#40;488,46&#41; Error&#58; Incompatible type for arg no. 3&#58; Got "<address>", expected "<procedure>"
LuaObject.pas&#40;516&#41; Fatal&#58; There were 10 errors compiling module, stopping
LuaObject.pas&#40;4,50&#41; Fatal&#58; Compilation aborted

Ick; at the moment I'm reconsidering trying to learn Lua using FPC. FPC just isn't very friendly to me no matter what I do, whenever I try.

[Robert Kosek]

I just noticed something, but Jeremy, why are you pushing a procedure like a pointer, when you aren't using the right type? If you adjust your types to include a lua_PCFunction (in Lua.pas) like so:[pascal]type
lua_CFunction = function(L : Plua_State) : Integer; cdecl;
lua_PCFunction = ^lua_CFunction;[/pascal]And then change your RegisterMethod and lua_pushcfunction to use the lua_PCFunction type it seems to work. You're treating the function like a pointer and FPC is choking all over itself on this. Either it says "I don't want an address!" or when you pass a function "where are the variables for the function?" and so it doesn't work either way in its present implementation.