EDIT: unfortunately LuaJIT was taken out of the comparison in the link below.

This &lt;a href=&quot;http://shootout.alioth.debian.org/u64/which-programming-languages-are-fastest.php&quot;&gt;comparison&lt;/a&gt; of programming languages shows that LuaJIT has an over tenfold improvement over the normal Lua implementation.
Why is the change so big? Is there something specific about Lua that makes it benefit a lot from JIT compilation?
Python is dynamically typed and compiled to bytecode as well, so why doesn&#39;t PyPy (that has JIT now, I believe) show such a large jump in performance?

Why is LuaJIT so good?

My directory structure looks like this:

    |-- ball.lua
    |-- entity.lua
    |-- test
        `-- ball_test.lua

I&#39;m using the following code in test/ball_test.lua to require ball.lua from the parent directory:

    package.path = package.path .. &quot;;../entity.lua&quot;
    require(&quot;entity&quot;)
    package.path = package.path .. &quot;;../ball.lua&quot;
    require(&quot;ball&quot;)

entity.lua is a dependency of ball.lua. So I require(&quot;entity&quot;) first otherwise I get a module &#39;entity.lua&#39; not found error. This seems like a hack, what&#39;s a better way to do this?


Is there a better way to require file from relative path in lua

Is LuaJava a must for this? Or can I embed Lua into Java without it?

How can I embed Lua in Java?

Many will found that this is repeating questions but i have gone through all the questions before asked about this topic but none worked for me.

I want to print full path name of the certain file format using ls command so far i found chunk of code that will print all the files in the directory but not full path.


    for i in io.popen(&quot;ls /mnt/mediashare/net/192.168.1.220_STORAGE_1d1b7&quot;):lines() do
      if string.find(i,&quot;%.*$&quot;) then 
         print(i) 
      end
    end

this will print out all the file in root diractory and subdiratory.

Output:

      0020111118223425.lvf
      2012
      2012 (2009).mp4
      3 Idiots
      Aashiqui 2
      Agneepath.mkv
      Avatar (2009)
      Captain Phillips (2013)
      Cocktail
      
  
I want output like:

      /mnt/mediashare/net/192.168.1.220_STORAGE_1d1b7/0020111118223425.lvf           [File in Root Directory]
      /mnt/mediashare/net/192.168.1.220_STORAGE_1d1b7/2012/2012.mkv
      /mnt/mediashare/net/192.168.1.220_STORAGE_1d1b7/2012 (2009).mp4                [File in Root Directory]
      /mnt/mediashare/net/192.168.1.220_STORAGE_1d1b7/3 Idiots/3 Idiots.mkv
      /mnt/mediashare/net/192.168.1.220_STORAGE_1d1b7/Aashiqui 2/Aashiqui 2.mkv
      /mnt/mediashare/net/192.168.1.220_STORAGE_1d1b7/Avatar (2009)/Avatar (2009).mkv
      /mnt/mediashare/net/192.168.1.220_STORAGE_1d1b7/Captain Phillips (2013).mkv
      /mnt/mediashare/net/192.168.1.220_STORAGE_1d1b7/Cocktail/Cocktail.mkv
    

**EDIT:**
I have used this all but its not working with my code in LUA.

when I used with my code it displays wrong directory

    for i in io.popen(&quot;ls -d $PWD/* /mnt/mediashare/net/192.168.1.220_STORAGE_1d1b7&quot;):lines() do
        if string.find(i,&quot;%.*$&quot;) then
          print(&quot;/mnt/mediashare/net/192.168.1.220_STORAGE_1d1b7/&quot;..i)
        end
      end

is not finding files in &quot;/mnt/mediashare/net/192.168.1.220_STORAGE_1d1b7&quot; insted its prints the machines root directory files.
    


List file using ls command in Linux with full path

I know [Love2D][1] and [Corona SDK][2] (for mobile devices). Is there any other game engines that use Lua you recommend?


  [1]: http://love2d.org/ &quot;Love2D&quot;
  [2]: https://coronalabs.com/

What is a good game engine that uses Lua?

When I do an &quot;os.execute&quot; in Lua, a console quickly pops up, executes the command, then closes down. But is there some way of getting back the console output only using the standard Lua libraries?

Get back the output of os.execute in Lua

According to the computer language benchmark game, the LuaJIT implementation [seems to beat every other JIT-ed dynamic language][1] (V8, Tracemonkey, PLT Scheme, Erlang HIPE) by **an order of magnitude**. 

I know that these benchmarks are not representative (as they say: &quot;Which programming language implementations have the fastest benchmark programs?&quot;), but this is still really impressive.

In practice, is it really the case? Someone have tested that Lua implementation?


  [1]: http://shootout.alioth.debian.org/u32/which-programming-languages-are-fastest.php?gpp=on&amp;luajit=on&amp;sbcl=on&amp;mzscheme=on&amp;hipe=on&amp;v8=on&amp;vw=on&amp;lua=on&amp;calc=chart

Is LuaJIT really faster than every other JIT-ed dynamic languages?

Is it possible to read the following from the local variable in Lua?

    local t = os.execute(&quot;echo &#39;test&#39;&quot;)
    print(t)

I just want to achieve this: whenever `os.execute` returns any value, I would like to use it in Lua - for example `echo &#39;test&#39;` will output `test` in the bash command line - is that possible to get the returned value (`test` in this case) to the Lua local variable?



Lua os.execute return value

I have seen the hash character &#39;#&#39; being added to the front of variables a lot in Lua.

What does it do? 

EXAMPLE

    -- sort AIs in currentlevel
    table.sort(level.ais, function(a,b) return a.y &lt; b.y end)
    local curAIIndex = 1
    local maxAIIndex = #level.ais
    for i = 1,#currentLevel+maxAIIndex do
        if level.ais[curAIIndex].y+sprites.monster:getHeight() &lt; currentLevel[i].lowerY then
            table.insert(currentLevel, i, level.ais[curAIIndex])
            curAIIndex = curAIIndex + 1
            if curAIIndex &gt; maxAIIndex then
                break
            end
        end
    end

Apologies if this has already been asked, I&#39;ve searched around on the internet a lot but I haven&#39;t seem to have found an answer. Thanks in advance!

What does # mean in Lua?

How can I convert a string to an integer in Lua?

I have a string like this:

    a = &quot;10&quot;

I would like it to be converted to 10, the number.

Lua string to int

I am confused about the difference between function calls via `.` and via `:`

    &gt; x = {foo = function(a,b) return a end, bar = function(a,b) return b end, }
    &gt; return x.foo(3,4)
    3
    &gt; return x.bar(3,4)
    4
    &gt; return x:foo(3,4)
    table: 0x10a120
    &gt; return x:bar(3,4)
    3

What is the `:` doing ?


Difference between . and : in Lua

I need to do a simple split of a string, but there doesn&#39;t seem to be a function for this, and the manual way I tested didn&#39;t seem to work. How would I do it?

Split string in Lua?

Sounds like a &quot;let me google it for you&quot; question, but somehow I can&#39;t find an answer. The Lua `#` operator only counts entries with integer keys, and so does `table.getn`:

    tbl = {}
    tbl[&quot;test&quot;] = 47
    tbl[1] = 48
    print(#tbl, table.getn(tbl))   -- prints &quot;1     1&quot;

    count = 0
    for _ in pairs(tbl) do count = count + 1 end
    print(count)            -- prints &quot;2&quot;

How do I get the number of _all_ entries without counting them?

How to get number of entries in a Lua table?

I have been dealing a lot with Lua in the past few months, and I really like most of the features but I&#39;m still missing something among those:

- Why is there no `continue`?
- What workarounds are there for it?

Why does Lua have no &quot;continue&quot; statement?

Given an array of x,y points, how do I sort the points of this array in clockwise order (around their overall average center point)? My goal is to pass the points to a line-creation function to end up with something looking rather &quot;solid&quot;, as convex as possible with no lines intersecting.

For what it&#39;s worth, I&#39;m using Lua, but any pseudocode would be appreciated.

**Update:** For reference, this is the Lua code based on Ciamej&#39;s excellent answer (ignore my &quot;app&quot; prefix):

    function appSortPointsClockwise(points)
        local centerPoint = appGetCenterPointOfPoints(points)
        app.pointsCenterPoint = centerPoint
        table.sort(points, appGetIsLess)
        return points
    end
    
    function appGetIsLess(a, b)
        local center = app.pointsCenterPoint
    
        if a.x &gt;= 0 and b.x &lt; 0 then return true
        elseif a.x == 0 and b.x == 0 then return a.y &gt; b.y
        end
    
        local det = (a.x - center.x) * (b.y - center.y) - (b.x - center.x) * (a.y - center.y)
        if det &lt; 0 then return true
        elseif det &gt; 0 then return false
        end
    
        local d1 = (a.x - center.x) * (a.x - center.x) + (a.y - center.y) * (a.y - center.y)
        local d2 = (b.x - center.x) * (b.x - center.x) + (b.y - center.y) * (b.y - center.y)
        return d1 &gt; d2
    end
    
    function appGetCenterPointOfPoints(points)
        local pointsSum = {x = 0, y = 0}
        for i = 1, #points do pointsSum.x = pointsSum.x + points[i].x; pointsSum.y = pointsSum.y + points[i].y end
        return {x = pointsSum.x / #points, y = pointsSum.y / #points}
    end

&lt;/code&gt;

Sort points in clockwise order?

I don&#39;t understand the rationale behind the decision of this part of Lua. Why does indexing start at 1? I have read (as many others did) [this great paper][1]. It seems to me a strange corner of a language that is very pleasant to learn and program. Don&#39;t get me wrong, Lua is just great but there has to be an explanation somewhere. Most of what I found (on the web) is just saying the index starts at 1. Full stop.

It would be very interesting to read what its designers said about the subject.

Note that I am &quot;very&quot; beginner in Lua, I hope I am not missing something obvious about tables.

  [1]: http://www.cs.utexas.edu/~EWD/ewd08xx/EWD831.PDF

Why do Lua arrays(tables) start at 1 instead of 0?

I&#39;m having trouble displaying the contents of a table which contains nested tables (n-deep). I&#39;d like to just dump it to std out or the console via a `print` statement or something quick and dirty but I can&#39;t figure out how. I&#39;m looking for the rough equivalent that I&#39;d get when printing an `NSDictionary` using gdb. 

How to dump a table to console?

What&#39;s the most efficient way to determine if a table is empty (that is, currently contains neither array-style values nor dict-style values)?

Currently, I&#39;m using `next()`:

    if not next(myTable) then
        -- Table is empty
    end

Is there a more efficient way?

Note: The `#` operator does not suffice here, as it only operates on the array-style values in the table - thus `#{test=2}` is indistinguishable from `#{}` because both return 0. Also note that checking if the table variable is `nil` does not suffice as I am not looking for nil values, but rather tables with 0 entries (i.e. `{}`).

Most efficient way to determine if a Lua table is empty (contains no entries)?

Is there a method for checking if a table contains a value ? I have my own (naive) function, but I was wondering if something &quot;official&quot; exists for that ? Or something more efficient...

    function table.contains(table, element)
      for _, value in pairs(table) do
        if value == element then
          return true
        end
      end
      return false
    end

By the way, the main reason I&#39;m using this functions is to use tables as sets, ie with no duplicate elements. Is there something else I could use ?

How to check if a table contains an element in Lua?

I simply love JavaScript. It&#39;s so elegant.

So, recently I have played with Lua via the [l&#246;ve2d](http://love2d.org) framework (nice!) - and I think Lua is also great. They way I see it, those two languages are *very* similar.

There are obvious differences, like

* syntax
* problem domain
* libraries
* types (a bit)

but which are the more subtle ones? Is there anything a JavaScript coder would take for granted that works in Lua just slightly different? Are there any pitfalls that may not be obvious to the experienced coder of one language trying the other one?

For example: in Lua, arrays and hashes are not separate (there are only tables) - in JavaScript, they are numerical Arrays and hashed Objects. Well, this is one of the more obvious differences.

But are there differences in variable scope, immutability or something like this?

subtle differences between JavaScript and Lua

Is there anyway to use inline conditions in Lua?

Such as:

    print(&quot;blah: &quot; .. (a == true ? &quot;blah&quot; : &quot;nahblah&quot;))

Inline conditions in Lua (a == b ? &quot;yes&quot; : &quot;no&quot;)?

I have a lua table that I use as a hashmap, ie with string keys :

    local map = { foo = 1, bar = 2 }

I would like to &quot;pop&quot; an element of this table identified by its key. There is a `table.remove()` method, but it only takes the index of the element to remove (ie a number) and not a generic key. I would like to be able to do `table.remove(map, &#39;foo&#39;)` and here is how I implemented it :

    function table.removekey(table, key)
        local element = table[key]
        table[key] = nil
        return element
    end

Is there a better way to do that ?


How to remove a lua table entry by its key?

I have a string in Lua and want to iterate individual characters in it. But no code I&#39;ve tried works and the official manual only shows how to find and replace substrings :(

    str = &quot;abcd&quot;
    for char in str do -- error
      print( char )
    end
    
    for i = 1, str:len() do
      print( str[ i ] ) -- nil
    end



How to iterate individual characters in Lua string?

In the Lua wiki I found a way to define default values for missing arguments:

	function myfunction(a,b,c)
		b = b or 7
		c = c or 5
		print (a,b,c)
	end

Is that the only way? The PHP style `myfunction (a,b=7,c=5)` does not seem to work. Not that the Lua way doesn&#39;t work, I am just wondering if this is the only way to do it.

Define default values for function arguments

In many languages you can concatenate strings on variable assignment.  I have a scenario, using the Lua programming language, where I need to append the output of a command to an existing variable.  Is there a functional equivalent in Lua to the below examples?

Examples of other languages:

    ===== PERL =====
    $filename = &quot;checkbook&quot;;
    $filename .= &quot;.tmp&quot;;
    ================

    ===== C# =====
    string filename = &quot;checkbook&quot;;
    filename += &quot;.tmp&quot;;
    ===============

Thank you in advance for your help.

Concatenation of strings in Lua

My assignment is how to do a for loop. I have figured it out in terms of numbers but cannot figure it out in terms of names. I would like to create a for loop that runs down a list of names. Following is what I have so far: 

    names = {&#39;John&#39;, &#39;Joe&#39;, &#39;Steve&#39;}
    for names = 1, 3 do
      print (names)
    end

I have tried some other things but it just doesn&#39;t work, the terminal always just lists 1, 2, 3... What I am doing wrong?

For Loop on Lua

I&#39;ve been trying to use Corona SDK&#39;s Facebook API to post the score on the game I&#39;m developing on facebook. However, I&#39;m having a problem with it. During the first time I try to post to facebook, I get this error after login and user authentication:

&gt; NSURLErrorDomain error code -999

Then, it won&#39;t post on facebook. What are possible causes of this error and how can I address it? I tried searching the web but couldn&#39;t find information about it. Thanks in advance.

By the way, I am not using webview on my app. Just the widget api and a show_dialog listener in my Facebook class.

NSURLErrorDomain error code -999 in iOS

I&#39;m trying to figure out the equivalent of:

    foo = []
    foo &lt;&lt; &quot;bar&quot;
    foo &lt;&lt; &quot;baz&quot;

I don&#39;t want to have to come up with an incrementing index. Is there an easy way to do this?

How do I append to a table in Lua

Is there a common way to get the current time in or with milliseconds?

There is `os.time()`, but it only provides full seconds.

Lua - Current time in milliseconds

How can I check if a file exists using Lua?

Check if a file exists with Lua

In a for loop, what is the difference between looping with pairs() and ipairs()? This page uses both: [Lua Docs][1]

With ipairs():

    a = {&quot;one&quot;, &quot;two&quot;, &quot;three&quot;}
    for i, v in ipairs(a) do
      print(i, v)
    end

Result:
  
    1	one
    2	two
    3	three


With pairs():

    a = {&quot;one&quot;, &quot;two&quot;, &quot;three&quot;}
    for i, v in pairs(a) do
      print(i, v)
    end

Result: 

    1	one
    2	two
    3	three


You can test it here: [Lua Demo][2]


  [1]: https://www.lua.org/pil/4.3.5.html &quot;Lua Docs&quot;
  [2]: https://www.lua.org/cgi-bin/demo

What is the difference of pairs() vs. ipairs() in Lua?

I need to merge two tables, with the contents of the second overwriting contents in the first if a given item is in both.  I looked but the standard libraries don&#39;t seem to offer this. Where can I get such a function?

How to merge two tables overwriting the elements which are in both?

I have a game project to re-implement [Breakout](https://en.wikipedia.org/wiki/Breakout_(video_game)). I want to display two words, each word on a line. They are joined by the bricks block. Inside, the top line is the first name, aligned left. The bottom line is the last name, aligned right. They are input from textboxes, and rendered as shown:

![As described above][1]

Each second that passes, the screen will add a configurable number of bricks to the grid (for example, five bricks per second) until the two words appear complete. I displayed a letter of the alphabet which is created from the matrix(0,1). 

...But I don’t know how to join them into one word. **How can I join these letters?**

This is what I&#39;ve gotten so far:

###Bricks.lua


    local Bricks = display.newGroup() -- static object
	local Events = require(&quot;Events&quot;)
	local Levels = require(&quot;Levels&quot;)
	local sound = require(&quot;Sound&quot;)
	local physics = require(&quot;physics&quot;)
	local Sprites = require(&quot;Sprites&quot;)
	local Func = require(&quot;Func&quot;)


	local brickSpriteData = 
	{
		{
			name = &quot;brick&quot;,
			frames = {Sprites.brick}
		},

		{
			name = &quot;brick2&quot;,
			frames = {Sprites.brick2}
		},

		{
			name = &quot;brick3&quot;,
			frames = {Sprites.brick3}
		},

	}

	-- animation table
	local brickAnimations = {}

	Sprites:CreateAnimationTable
	{
		spriteData = brickSpriteData,
		animationTable = brickAnimations
	}

	-- get size from temp object for later use
	local tempBrick = display.newImage(&#39;red_apple_20.png&#39;,300,500)
	--local tempBrick = display.newImage(&#39;cheryGreen2.png&#39;,300,500)
	local brickSize =
	{
		width = tempBrick.width, 
		height = tempBrick.height
	}
	--tempBrick:removeSelf( )


	----------------
	-- Rubble -- needs to be moved to its own file
	----------------

	local rubbleSpriteData =
	{
		{
			name = &quot;rubble1&quot;,
			frames = {Sprites.rubble1}
		},

		{
			name = &quot;rubble2&quot;,
			frames = {Sprites.rubble2}
		},

		{
			name = &quot;rubble3&quot;,
			frames = {Sprites.rubble3}
		},

		{
			name = &quot;rubble4&quot;,
			frames = {Sprites.rubble4}
		},

		{
			name = &quot;rubble5&quot;,
			frames = {Sprites.rubble5}
		},

	}

	local rubbleAnimations = {}
	Sprites:CreateAnimationTable
	{
		spriteData = rubbleSpriteData,
		animationTable = rubbleAnimations
	}

	local totalBricksBroken = 0 -- used to track when level is complete
	local totalBricksAtStart = 0

	-- contains all brick objects
	local bricks = {}


	local function CreateBrick(data)

		-- random brick sprite
		local obj = display.newImage(&#39;red_apple_20.png&#39;)
		local objGreen = display.newImage(&#39;cheryGreen2.png&#39;)
		obj.name = &quot;brick&quot;
		obj.x = data.x --or display.contentCenterX
		obj.y = data.y --or 1000
		obj.brickType = data.brickType or 1
		obj.index = data.index

		function obj:Break()
		
			totalBricksBroken =  totalBricksBroken + 1
			bricks[self.index] = nil
			obj:removeSelf( )
			sound.play(sound.breakBrick)

		end

		function obj:Update()
			if(self == nil) then
				return
			end 

			if(self.y &gt; display.contentHeight - 20) then
				obj:Break()
			end 
		end 
		if(obj.brickType ==1) then
			physics.addBody( obj, &quot;static&quot;, {friction=0.5, bounce=0.5 } )
		elseif(obj.brickType == 2) then
		 	physics.addBody( objGreen,&quot;static&quot;,{friction=0.2, bounce=0.5, density = 1 } )
		end 

		return obj
	end

	local currentLevel = testLevel
	-- create level from bricks defined in an object
	-- this allows for levels to be designed
	local function CreateBricksFromTable(level)

		totalBricksAtStart = 0
		local activeBricksCount = 0
		for yi=1, #level.bricks do
			for xi=1, #level.bricks[yi] do
				-- create brick?
				if(level.bricks[yi][xi] &gt; 0) then
					local xPos
					local yPos
					if(level.align == &quot;center&quot;) then
						--1100-((99*16)*0.5)
						xPos = display.contentCenterX- ((level.columns * brickSize.width) * 0.5/3) + ((xi-1) * level.xSpace)--display.contentCenterX 
						--xPos = 300 +(xi * level.xSpace)
						yPos = 100 + (yi * level.ySpace)--100
					else
						xPos = level.xStart + (xi * level.xSpace)
						yPos = level.yStart + (yi * level.ySpace)
					end

					local brickData = 
			  		{
				 		x = xPos,
						y = yPos,
						brickType = level.bricks[yi][xi],
						index = activeBricksCount+1
					}
					bricks[activeBricksCount+1] = CreateBrick(brickData)
				
					activeBricksCount = activeBricksCount + 1

				end

			end 

		end
		
		totalBricks = activeBricksCount
		totalBricksAtStart = activeBricksCount


	end

	-- create bricks for level --&gt; set from above functions, change function to change brick build type
	local CreateAllBricks = CreateBricksFromTable
	-- called by a timer so I can pass arguments to CreateAllBricks
	local function CreateAllBricksTimerCall()
		CreateAllBricks(Levels.currentLevel)
	end 
	-- remove all brick objects from memory
	local function ClearBricks()

		for i=1, #bricks do
			bricks[i] = nil
		end

	end
	-- stuff run on enterFrame event
	function Bricks:Update()

	-- update individual bricks
		if(totalBricksAtStart &gt; 0) then
			for i=1, totalBricksAtStart do
				-- brick exists?
				if(bricks[i]) then
					bricks[i]:Update()
				end 
			end 
		end
		-- is level over?
		if(totalBricksBroken == totalBricks) then
			Events.allBricksBroken:Dispatch()
		end

	end
	----------------
	-- Events
	----------------
	function Bricks:allBricksBroken(event)
		-- cleanup bricks
		ClearBricks()
		local t = timer.performWithDelay( 1000, CreateAllBricksTimerCall)
		--CreateAllBricks()
		totalBricksBroken = 0		
		
		-- play happy sound for player to enjoy
		sound.play(sound.win)

		print(&quot;You Win!&quot;)
	end
	Events.allBricksBroken:AddObject(Bricks)
	CreateAllBricks(Levels.currentLevel)
	return Bricks

###Levels.lua

    
	local Events = require(&quot;Events&quot;)
	local Levels = {}
	local function MakeLevel(data)
		local level = {}
		level.xStart = data.xStart or 100
		level.yStart = data.yStart or 100
		level.xSpace = data.xSpace or 23
		level.ySpace = data.ySpace or 23
		level.align = data.align or &quot;center&quot;
		level.columns = data.columns or #data.bricks[1]
		level.bricks = data.bricks --&gt; required
		return level
	end
	Levels.test4 = MakeLevel
	{
		bricks =
		{
			{0,2,0,0,2,0,0,2,0},
			{0,0,2,0,2,0,2,0,0},
			{0,0,0,0,2,0,0,0,0},
			{1,1,2,1,1,1,2,1,1},
			{0,0,0,0,1,0,0,0,0},
			{0,0,0,0,1,0,0,0,0},
			{0,0,0,0,1,0,0,0,0},
		}
	}

	Levels.test5 = MakeLevel
	{
		bricks =
		{		
	        			{0,0,0,1,0,0,0,0},
					 	 {0,0,1,0,1,0,0,0},
					 	 {0,0,1,0,1,0,0,0},
					 	 {0,1,0,0,0,1,0,0},
					 	 {0,1,1,1,1,1,0,0},
					 	 {1,0,0,0,0,0,1,0},
					 	 {1,0,0,0,0,0,1,0},
					 	 {1,0,0,0,0,0,1,0},
					 	 {1,0,0,0,0,0,1,0}
		}
	}
	-- Levels.test6 = MakeLevel2
	-- {
	-- 	bricks =
	-- 	{
	----A 		  &quot;a&quot; = {{0,0,0,1,0,0,0,0},
	-- 				 	 {0,0,1,0,1,0,0,0},
	-- 				 	 {0,0,1,0,1,0,0,0},
	-- 				 	 {0,1,0,0,0,1,0,0},
	-- 				 	 {0,1,1,1,1,1,0,0},
	-- 				 	 {1,0,0,0,0,0,1,0},
	-- 				 	 {1,0,0,0,0,0,1,0},
	-- 				 	 {1,0,0,0,0,0,1,0},
	-- 				 	 {1,0,0,0,0,0,1,0}},
	----B
	-- 		      &quot;b&quot; = {{1,1,1,1,0,0,0},
	-- 				 	 {1,0,0,0,1,0,0},
	-- 				 	 {1,0,0,0,1,0,0},
	-- 				 	 {1,0,0,0,1,0,0},
	-- 				 	 {1,1,1,1,0,0,0},
	-- 				 	 {1,0,0,0,1,0,0},
	-- 				 	 {1,0,0,0,0,1,0},
	-- 				 	 {1,0,0,0,0,1,0},
	-- 				 	 {1,1,1,1,1,0,0}},
	--...........
	--.......
	--...
	-- --Z
	-- 		 	   &quot;z&quot;= {{1,1,1,1,1,1,1,0},
	-- 				 	 {0,0,0,0,0,1,0,0},
	-- 				 	 {0,0,0,0,1,0,0,0},
	-- 				 	 {0,0,0,0,1,0,0,0},
	-- 				 	 {0,0,0,1,0,0,0,0},
	-- 				 	 {0,0,1,0,0,0,0,0},
	-- 				 	 {0,0,1,0,0,0,0,0},
	-- 				 	 {0,1,0,0,0,0,0,0},
	-- 				 	 {1,1,1,1,1,1,1,0}}	
	-- 	}
	-- }
	-- stores all levels in ordered table so that one can be selected randomly by index
	Levels.levels = 
	{
		--Levels.test4,
		 Levels.test5
		-- Levels.test6,
	}
	function Levels:GetRandomLevel()
		return self.levels[math.random(#Levels.levels)]
	end
	Levels.notPlayedYet = {}
	Levels.currentLevel = Levels:GetRandomLevel()
	-- Events
	function Levels:allBricksBroken(event)
		self.currentLevel = Levels:GetRandomLevel()
	end
	Events.allBricksBroken:AddObject(Levels)
	return Levels

 
The work I&#39;ve done thus far (same as above) as an external download: http://www.mediafire.com/download/1t89ftkbznkn184/Breakout2.rar


  [1]: http://i.stack.imgur.com/Hl5Ga.png


Join tiles in Corona SDK into one word for a Breakout game grid?

I&#39;m confused what purpose **[Mongrel2][1]** serves/provides that **[nginx][2]** doesn&#39;t already do.

*(Yes, I&#39;ve read the [manual][3] but I must to be too much of a noob to understand how it&#39;s fundamentally different than nginx)*

My current web application stack is: &lt;br&gt;
- **nginx**: webserver &lt;br&gt;
- **Lua**: programming language &lt;br&gt;
- **FastCGI + LuaJIT**: to connect nginx to Lua &lt;br&gt;
- **Postgres**: database


  [1]: http://mongrel2.org
  [2]: http://nginx.org
  [3]: http://mongrel2.org/static/mongrel2-manual.html

Why use Mongrel2?

So Lua seems ideal for implementing secure &quot;user scripts&quot; inside my application.

However, most examples of embedding lua seem to include loading all the standard libraries, including &quot;io&quot; and &quot;package&quot;.

So I can exclude those libs from my interpreter, but even the base library includes the functions &quot;dofile&quot; and &quot;loadfile&quot; which access the filesystem.

How can I remove/block any unsafe functions like these, without just ending up with an interpreter that doesn&#39;t even have basic stuff like the &quot;ipairs&quot; function?

How can I create a secure Lua sandbox?

So, I have a table something along these lines:

    arr =
    {
      apples = { &#39;a&#39;, &quot;red&quot;, 5 },
      oranges = { &#39;o&#39;, &quot;orange&quot;, 12 },
      pears = { &#39;p&#39;, &quot;green&quot;, 7 }
    }

It doesn&#39;t seem like it&#39;s possible to access them based on their index, and the values themselves are tables, so I just made the first value of the nested table the index of it, so it now looks like this:

    arr =
    {
      apples = { 0, &#39;a&#39;, &quot;red&quot;, 5 },
      oranges = { 1, &#39;o&#39;, &quot;orange&quot;, 12 },
      pears = { 2, &#39;p&#39;, &quot;green&quot;, 7 }
    }

So, now any time I use one of these tables, I know what the index is, but still can&#39;t get to the table using the index, so I started to write a function that loops through them all, and check the indexes until it finds the right one. Then I realized... how can I loop through them if I can&#39;t already refer to them by their index? So, now I&#39;m stuck. I really want to be able to type arr.apples vs arr[1] most of the time, but of course it&#39;s necessary to do both at times.

How to iterate through table in Lua?

I need a Torch command that checks if two tensors have the same content, and returns TRUE if they have the same content.

For example:

    local tens_a = torch.Tensor({9,8,7,6});
    local tens_b = torch.Tensor({9,8,7,6});
    
    if (tens_a EQUIVALENCE_COMMAND tens_b) then ... end

What should I use in this script instead of `EQUIVALENCE_COMMAND` ?

I tried simply with `==` but it does not work. 

How to check if two Torch tensors or matrices are equal?

I need to make a conditional that is true if a particular matching text is found at least once in a string of text, e.g.:

    str = &quot;This is some text containing the word tiger.&quot;
    if string.match(str, &quot;tiger&quot;) then
        print (&quot;The word tiger was found.&quot;)
    else
        print (&quot;The word tiger was not found.&quot;)

How can I check if the text is found somewhere in the string?

How to check if matching text is found in a string in Lua?

I&#39;m currently learning lua. regarding pattern-matching in lua I found the following sentence in the lua documentation on lua.org:

&gt; Nevertheless, pattern matching in Lua is a powerful tool and includes some features that are difficult to match with standard POSIX implementations.

As I&#39;m familiar with posix regular expressions I would like to know if there are any common samples where lua pattern matching is &quot;better&quot; compared to regular expression -- or did I misinterpret the sentence? and if there are any common examples: why is any of pattern-matching vs. regular expressions better suited?


Lua pattern matching vs. regular expressions

I&#39;ve some currently some Lua code using the following syntax:

    if (foo == nil or foo == &#39;&#39;) then
        foo = &quot;some default value&quot;
    end
 
The goal of the if condition is to test foo is neither an empty string, neither a nil value.

Can this code be simplified in one if test instead two?

Check if a string isn&#39;t nil or empty in Lua

Recently I wrote a bit of Lua code something like:

    local a = {}
    for i = 1, n do
       local copy = a
       -- alter the values in the copy
    end

Obviously, that wasn&#39;t what I wanted to do since variables hold references to an anonymous table not the values of the table themselves in Lua.  This is clearly laid out in [Programming in Lua](http://www.lua.org/pil/2.5.html), but I&#39;d forgotten about it.

So the question is what should I write instead of `copy = a` to get a copy of the values in `a`?



How do you copy a Lua table by value?

Lua occupies a good place in the space of languages that can be embedded.  Are the primary ideas behind Lua&#39;s design new ideas from the implementors, or is Lua primarily a well-executed combination of well-established ideas?

Comparison of properties and features of Lua to other PLs are particularly appropriate.

Is Lua based primarily on well-established programming-language ideas?

If I have a list of items like this:

    local items = { &quot;apple&quot;, &quot;orange&quot;, &quot;pear&quot;, &quot;banana&quot; }

how do I check if &quot;orange&quot; is in this list?

In Python I could do:

    if &quot;orange&quot; in items:
        # do something

Is there an equivalent in Lua?

Search for an item in a Lua list

I am working on an embedded system running Linux on a DSP. Now we want to make some parts of it scriptable and we are looking for a nice embeddable scripting language. These scripts should integrate nicely with our existing C++ code base, be small and fast.

I understand that Lua is the industry choice for problems like this. We will probably go with Lua because it is tried-and-true and proven to be stable and so on. However, as a programming language it has some rather quirky corners.

So, what alternatives are out there for embeddable languages?

__EDIT:__

This is about a year later.  

We actually used Lua on our embedded system and it performs marvelously well. Over time, we added more and more scripting support to more and more parts of the project and that really helped to bring it along.  

Performance is outstanding, really. Even rather complex operations that involve searching through long arrays or fancy string operations perform surprisingly well. We basically never ran into Lua related performance problems at all.

Interfacing with C functions is very straightforward and works really well. This allowed us to grow the scripting system painlessly.

Finally, we were astounded at how flexible Lua proved to be. Our Lua interpreter has to run on a system with a nonstandard memory allocator and without support for the double data type. There are two well-documented places in one header file we had to modify to make Lua work on that system. It is really well suited for embedding!

Alternatives to Lua as an embedded language?

This is a question I&#39;ve been mildly irritated about for some time and just never got around to search the answer to.

However I thought I might at least ask the question and perhaps someone can explain.

Basically many languages I&#39;ve worked in utilize syntactic sugar to write (using syntax from C++):

    int main() {
        int a = 2;
        a += 3; // a=a+3
    }

while in lua the `+=` is not defined, so I would have to write `a=a+3`, which again is all about syntactical sugar. when using a more &quot;meaningful&quot; variable name such as: `bleed_damage_over_time` or something it starts getting tedious to write: 

    bleed_damage_over_time = bleed_damage_over_time + added_bleed_damage_over_time 

instead of: 

    bleed_damage_over_time += added_bleed_damage_over_time

So I would like to know not how to solve this if you don&#39;t have a nice solution, in that case I would of course be interested in hearing it; but rather why lua doesn&#39;t implement this syntactical sugar.


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