Lua's weird return values are basically just exposing the fact that it's a stack-based VM and letting the user take advantage of that. foo(1, return_two_values(

Lua's weird return values are basically just exposing the fact that it's a stack-based VM and letting the user take advantage of that. foo(1, return_two_values(arg), 2) pushes 1 onto the stack, pushes arg onto the stack, calls return_two_values (which pops one value from the stack and pushes two new ones), pushes 2 onto the stack, and then calls foo, resulting in foo being called with four arguments. With this design you get zero-overhead (you save the construction of a table) multiple return values for free, since it simply requires a trivial bit of syntax and no error checking to verify that a function only left zero or one values on the stack. Lists aren't exposed as concrete things that can be passed around because the really aren't things at all.