Function lua_concat 

pub unsafe extern "C-unwind" fn lua_concat(
    L: *mut lua_State,
    n: c_int,
)

Concatenates n values from the stack into a string.

This function pops n values from the top of the stack, concatenates them into a string, and pushes the resulting string onto the top of the stack. When n is 0 an empty string is pushed onto the stack.