LUA: how do you save someones progress?

You basically need to:

• Save the state of the program when the program ends
• Restore the state of the program when the program starts

There are several ways to store the state, the simplest way would be to create a file and store the state inside. One could also use the Windows Registry, a database, a remote server, etc.

A simple example:

function FileExists (Filename)
  local File = io.open(Filename, "r")
  if File then
    File:close()
  end
  return File
end

function CreateFile (Filename)
  local File = io.open(Filename, "w")
  if File then
    File:close()
  end
end

ProgramStateFile = "program-state.txt"

if not FileExists(ProgramStateFile) then
  print("you've been here for the first time.")
else
  print("you're here for second or more time")
end

CreateFile(ProgramStateFile)

In this example, the state is only the existence of the state file. Obviously, you can extend this example by writing additional information inside the file.

function ReadState (Filename)
  local File = io.open(Filename, "r")
  local State
  if File then
    State = File:read("a")
    File:close()
  end
  return State
end

function WriteState (Filename, State)
  local File = io.open(Filename, "w")
  if File then
    File:write(State)
    File:close()
  end
end

ProgramStateFile = "program-state.txt"

if ReadState(ProgramStateFile) ~= "PROGRAM-FINISHED" then
  print("you've been here for the first time.")
else
  print("you're here for second or more time")
end

WriteState(ProgramStateFile, "PROGRAM-FINISHED")

Finally, please note that there are many formats already existing to store the states: INI file, XML, JSON, etc. For Lua, you could also use a serialization library in order to store a Lua table directly inside a file. I would personally recommend the binser library.