Getting Started with LuaJ

Maven:

<dependency>
  <groupId>io.github.taoguan</groupId>
  <artifactId>luaj</artifactId>
  <version>1.0.3</version>
</dependency>

1 - Introduction

Features of Luaj

Luaj is a lua interpreter based on the 5.3.x version of lua with the following features in mind:

• Not support goto and label statement
• Support continue statement
• Java-centric implementation of lua vm built to leverage standard Java features.
• Lightweight, high performance execution of lua, can direct be compiled to java bytecode.

2 - Syntax BNF

chunk ::= block

block ::= {stat} [retstat]

stat ::=  ';' |
varlist '=' explist |
functioncall |
break |
continue |
do block end |
while exp do block end |
repeat block until exp |
if exp then block {elseif exp then block} [else block] end |
for Name '=' exp ',' exp [',' exp] do block end |
for namelist in explist do block end |
function funcname funcbody |
local function Name funcbody |
local namelist ['=' explist]

retstat ::= return [explist] [';']

funcname ::= Name {'.' Name} [':' Name]

varlist ::= var {',' var}

var ::=  Name | prefixexp '[' exp ']' | prefixexp '.' Name

namelist ::= Name {',' Name}

explist ::= exp {',' exp}

exp ::=  nil | false | true | Numeral | LiteralString | '...' | functiondef |
prefixexp | tableconstructor | exp binop exp | unop exp

prefixexp ::= var | functioncall | '(' exp ')'

functioncall ::=  prefixexp args | prefixexp ':' Name args

args ::=  '(' [explist] ')' | tableconstructor | LiteralString

functiondef ::= function funcbody

funcbody ::= '(' [parlist] ')' block end

parlist ::= namelist [',' '...'] | '...'

tableconstructor ::= '{' [fieldlist] '}'

fieldlist ::= field {fieldsep field} [fieldsep]

field ::= '[' exp ']' '=' exp | Name '=' exp | exp

fieldsep ::= ',' | ';'

binop ::=  '+' | '-' | '*' | '/' | '//' | '^' | '%' |
'&' | '~' | '|' | '>>' | '<<' | '..' |
'<' | '<=' | '>' | '>=' | '==' | '~=' |
and | or

unop ::= '-' | not | '#' | '~'

3 - Examples

3.1 Lua script

grammar-test.lua :

#!/bin/luaj

-- varlist '=' explist
--[[long comment]]
gvar11, gvar21, gvar22, gvar41, gvar42, gvar43 = nil, false, true, 'test1', "test2", [[long string\n, hello]]
gvar31, gvar32, gvar33, gvar34, gvar35, gvar36 = 10, -12, 123456789457, -0XFE, 123456789456.12, 1.2345678945613E11
gvar51, gvar52, gvar53 = {3,'test1', false}, {test1=34, ['test2']=55}, {test1=34, ['test2']=55, 4, 7, 9, [2]=8, [100]=53}
print(gvar11,gvar21,gvar22,gvar41,gvar42,gvar43)
print(gvar31,gvar32,gvar33,gvar34,gvar35,gvar36)
print(gvar51,gvar52,gvar53);

print(gvar53['test2']);
gvar53['test2']=80
print(gvar53['test2']);

local var11, var21, var22, var41, var42, var43 = nil, false, true, 'test1', "test2", [[long string\n, hello]]
local var31, var32, var33, var34, var35, var36 = 10, -12, 123456789457, -0XFE, 123456789456.12, 1.2345678945613E11
local var51, var52, var53 = {3,'test1', false}, {test1=34, ['test2']=55}, {test1=34, ['test2']=55, 4, 7, 9, [2]=8, [100]=53}
print(var11, var21, var22, var41, var42, var43)
print(var31, var32, var33, var34, var35, var36)
print(var51, var52, var53);

-- function funcname funcbody
function var52.addVar(self,...)
    local arg = {...}
    local len = #arg
    print('arg len = '..len)
    local result = 0;
    for i,v in ipairs(arg) do
      print('i='..i..';v='..v)
      if i == 1 then continue end
      if i == 3 then break end
      result = result + v
    end
    return result
end

function var52:minusVar(...)
    local arg = {...}
    local len = #arg
    print('arg len = '..len)
    local result;
    for i,v in ipairs(arg) do
      if i == 1 then continue end
      if result == nil then result = v end
      result = result - v
    end
    return result
end

-- functioncall
local testAddVar1 = var52.addVar(var52, 1,2,3,4,5)
local testAddVar2 = var52:addVar(1,2,3,4,6)
print(testAddVar1, testAddVar2)
local testMinusVar1 = var52.minusVar(var52, 1,2,3,4,5)
local testMinusVar2 = var52:minusVar(1,2,3,4,6)
print(testMinusVar1, testMinusVar2)

-- call java method
local javesystem = luajava.bindClass("java.lang.System")
local curTime = javesystem:currentTimeMillis();
print(curTime)
local date = luajava.newInstance("java.util.Date")
print(date.getTime(date))
print(date:getTime())

-- ArithOp test
local var31, var32= 2, -3
print(var31 + var32, var31 - var32, var31 * var32, var32 / var31, var32 // var31, var31 ^ var32, var32 % var31)
print(var31 & var32, var31 | var32, var31 ~ var32, ~var31)
print(var31 << var32, var31 >> var32)
print(var31 > var32, var31 >= var32, var31 < var32, var31 <= var32, var31 == var32, var31 ~= var32)

local var21, var22 = false, true
print(var21 and var22, var21 or var22, not var21)
print(var21, var22)
local fun1 = function()
     local var21, var22 = 7, 8
     local var33 = var31 * var32
     print(var21, var22)
     print(string.format('var33=%s', var33))
    end
fun1()
print(var21, var22)

local testContinue1 = 1
while testContinue1 < 10
do
    if testContinue1 == 5 then
    testContinue1 = testContinue1 + 1;
    continue end
    if testContinue1 == 7 then break end
    print('testContinue1='..testContinue1)
    testContinue1 = testContinue1 + 1
end
print('testContinue1-done')

local testContinue2 = 1
repeat
    if testContinue2 == 5 then
    testContinue2 = testContinue2 + 1;
    continue end
    if testContinue2 == 7 then break end
    print('testContinue2='..testContinue2)
    testContinue2 = testContinue2 + 1
until testContinue2 >= 10
print('testContinue2-done')

for testContinue3 = 1,10,1
do
    if testContinue3 == 5 then
    testContinue3 = testContinue3 + 1;
    continue end
    if testContinue3 == 7 then break end
    print('testContinue3='..testContinue3)
    testContinue3 = testContinue3 + 1
end
print('testContinue3-done')

local testContinue4Table = {4, 5, 6, 7, 8, 9, 10, 11, 12, 13}
for i, v in ipairs(testContinue4Table)
    do
    if i == 5 then
    continue end
    if i == 7 then break end
    print('testContinue4='..i..'-v:'..v)
end
print('testContinue4-done')

return var52

3.2 Java execute lua script

String luaFileName = AppTest.class.getClassLoader().getResource("grammar-test.lua").toURI().getPath();
Globals globals = JsePlatform.standardGlobals();
//LuaJC.install(globals); // You can use LuaJC to improve performance. It will compile lua script to java bytecode using BCEL.
LuaValue result = globals.loadfile(luaFileName).call();
System.out.println(result);

// java call lua method
LuaValue func = result.get(LuaValue.valueOf("addVar"));
int funcResult  = func.invoke(LuaValue.varargsOf(new LuaValue[]{result, LuaValue.valueOf(1),
        LuaValue.valueOf(2), LuaValue.valueOf(3)})).arg1().checkint();
System.out.println(String.format("funcResult=%s", funcResult));
Prototype p = globals.compilePrototype(new FileInputStream(luaFileName), "grammar-test");
Print.print(p);