path up until current module (usually the current directory)

here.lua

local prefix = ... and (...):match '(.-%.?)[^%.]+$' or ''
print( prefix )
--preserves last dot
--possible improvement: get module separator from package.config, usually not needed
--[[examples
  require 'module.submodule'
  module.
  require 'long.path.to.submodule'
  long.path.to.
  dofile 'module.lua'
  --prints empty string, fault tolerant
]]
require( prefix..'othersubmodule' )
--won't blow up if (...) is nil
--does not need extra dot