This is a proof-of-concept modification of the Lua programming language.

It allows updating the behavior of a program while the program is executing. Functions can even be updated if they contain loops which are currently executing, or coroutines which are suspended in them.

Updates in this system are performed by sending the updated program source file to the running virtual machine using ZeroMQ. The virtual machine then suspends the executing program, and executes the updated version. Annotations in the source code are used to record which functions are eligible for patching. After the changes are recorded, the original program resumes executing. While it is executing, on all backwards jumps the virtual machine attempts to transition the current frame to an updated version of the function.

Note that as a proof-of-concept the system has several limitations. For example, new constants cannot be used in the updated version of the function.

Example usage:

After installing ZeroMQ headers and building the system using make, load (src/lua example/hello1.lua) this program, which should output Hello repeatedly.

hello1.lua:

function main()
  while true do
    print('Hello')
  end
end

live.patch('main', main)

live.start(main)

Then, patch the program to version 2 (run src/patch.py example/hello2.lua).

hello2.lua:

world = ' World'

function main()
  while true do
    print('Hello' .. world)
  end
end

live.patch('main', main)

live.start(main)

The program should start outputing Hello World, after all buffers clear.