“main” function in Lua?

Question

In python, one would usually define a main function, in order to allow the script to be used as module (if needed):

def main():
    print(\"Hello world\")
           


        

Answer 1

When Lua requires a module, it passes it the name it's been required with as varargs (...).

So, if your script doesn't intend to take any arguments (from the command line or otherwise), you can use something like

if ... then
  return this_mod --module case
else
  main() --main case
end

Note, however, that this isn't foolproof in the (entirely) possible case that you take arguments. However, at this point, you can combine this with Lukasz's answer to get:

if not package.loaded[...] then
  --main case
else --module case
end

Still not perfect (for instance, if the script is called with a first argument of string or the name of some other already-loaded module), but likely good enough. In other situations, I defer to MattJ's answer.