Live coding on Linux with LÖVE

[purplehuman]

I don't know if everybody knows this, but I just recently figured it out, so I decided to share it if anyone else needs it.

To see the changes to your main.lua file live, add these lines to your love.update() function:

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if love.filesystem.load("main.lua") == nil then
     love.timer.sleep(1)
     love.filesystem.load("main.lua")()
end

Then run your game in the game directory with

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love .

(Note the dot at the end.)

Now when you make a change in the main.lua file and save, the running game will be updated. It doesn't reset the global variables, so it's great to code live. I use it for rapid prototyping.

What we do here in the code is to tell LÖVE if main.lua isn't available, wait a little and reload main.lua. It's a trick using a filesystem feature. When main.lua is saved, the old version of the file is removed for a moment before being replaced by the new version. I don't know if this works on Windows or Mac OS X though.

EDIT: I just realized that it's not about the filesystem, but about the text editor I use. I use vim for development, and vim seems to remove the old file when saving which causes LÖVE to throw an error. That's why I couldn't run only this line:

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love.filesystem.load("main.lua")()

But in gedit this line alone works fine.

[zorg]

The following code is more straightforward, and doesn't use tricks that may be either unpredictable or not cross-platform; nor does it block for 1 second per update:

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local lastModified
function love.load()
  lastModified = os.time()
end
function love.update(dt)
  if love.filesystem.getLastModified('main.lua') > lastModified then
    love.filesystem.load('main.lua')()
    lastModified = os.time()
  end
end

This checks the last modified time of the main.lua file, and if it's newer than what we set in love.load, it reloads it, and stores the date the newest update happened.
You could also use a timer, 4 times per second or so, or combine that with this method as well, it may reduce cpu or hdd/ssd/usb usage. (depending on where the main.lua file is located)
Also, this does not check / protect against code errors or editor-induced file existence failure idiosyncrasies, so if the new main.lua has some error in it, it will stop execution; there are ways around these though.
I do something similar like this in my codebase, but that's contained per-gamestate (i.e. i'm never modifying main.lua), don't know what the possible repercussions may be if you do this though.

[purplehuman]

Thanks zorg! Yours is a better solution than mine. I just realized that problem wasn't about the filesystem, but the text editor I use. Vim seems to remove the old file when saving. But I will use your solution, since it's more elegant.

EDIT: I just tried your solution. I'm afraid when using vim, it throws the same error. For a moment, the file isn't there, so LÖVE throws an error when you compare the last modified time. My solution might be vim specific maybe, but it works for me.

[zorg]

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local lastModified
function love.load()
	lastModified = os.time()
end
function reload(path)
	local result, chunk
	result, chunk = pcall(love.filesystem.load, path)
	if not result then print("chunk error: " .. chunk) return false end
	result, chunk = pcall(chunk,...)
	if not result then print("exec. error: " .. chunk) return false end
	return true
end
function love.update(dt)
	if love.filesystem.getLastModified('main.lua') > lastModified then
	if reload('main.lua') then
		lastModified = os.time()
	end
  end
end

This is one step closer; now if it fails to read or execute the chunk, it won't mess with the modification time it stores, so after fixing the source, it will be able to reload it.

[yetneverdone]

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local lastModified
function love.load()
	lastModified = os.time()
end
function reload(path)
	local result, chunk
	result, chunk = pcall(love.filesystem.load, path)
	if not result then print("chunk error: " .. chunk) return false end
	result, chunk = pcall(chunk,...)
	if not result then print("exec. error: " .. chunk) return false end
	return true
end
function love.update(dt)
	if love.filesystem.getLastModified('main.lua') > lastModified then
	if reload('main.lua') then
		lastModified = os.time()
	end
  end
end

This is one step closer; now if it fails to read or execute the chunk, it won't mess with the modification time it stores, so after fixing the source, it will be able to reload it.

Throws an error:
'...' outside a vararg function near '...'

[zorg]

Just remove the '...' from pcall(chunk,...); to be honest, i have no idea what the purpose of that was...

Late edit: The purpose was probably to send in arguments to the chunk itself, so those could be accessed by doing local args = {...} or something at the top of the loaded file; i just forgot to give the reload function the same ... parameter in the definition.

[Darlex]

Doesn't work on Android
Just stays on black

[zorg]

Doesn't work on Android
Just stays on black

Which one, and how are you trying to run it?

[Darlex]

I downloaded the LÖVE2D app on my phone and I just loaded the main.lua on it, But doesn't work

Pd: Sorry, my English is so bad

[Darlex]

Code: Select all

local lastModified
function love.load()
	lastModified = os.time()
end
function reload(path)
	local result, chunk
	result, chunk = pcall(love.filesystem.load, path)
	if not result then print("chunk error: " .. chunk) return false end
	result, chunk = pcall(chunk)
	if not result then print("exec. error: " .. chunk) return false end
	return true
end
function love.update(dt)
	if love.filesystem.getLastModified('main.lua') > lastModified then
	if reload('main.lua') then
		lastModified = os.time()
	end
  end
end

This one..