code: func (l *State) ToString(index int) (s string, ok bool) {
  	if s, ok = toString(l.indexToValue(index)); ok { // Bug compatibility: replace a number with its string representation.
  		l.setIndexToValue(index, s)
  	}
  	return
  }
docs: // ToString  converts the Lua value at index to a Go string.  The Lua value
  // must also be a string or a number; otherwise the function returns
  // false for its second return value.
  //
  // http://www.lua.org/manual/5.2/manual.html#lua_tolstring