lua_concat

void lua_concat (lua_State *L, int n);

Concatenates the n values at the top of the stack, pops them, and leaves the result at the top. If n is 1, the result is the single string on the stack (that is, the function does nothing); if n is 0, the result is the empty string. Concatenation is done following the usual semantics of Lua (see §2.5.4).