code: func (l *State) Concat(n int) {
  	l.checkElementCount(n)
  	if n >= 2 {
  		l.concat(n)
  	} else if n == 0 { // push empty string
  		l.apiPush("")
  	} // else n == 1; nothing to do
  }
docs: // Concat 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 value
  // on the stack (that is, the function does nothing); if n is 0, the result
  // is the empty string. Concatenation is performed following the usual
  // semantic of Lua.
  //
  // http://www.lua.org/manual/5.2/manual.html#lua_concat