How to call a function not by its name in lua script?

[BrillyWu <brillywu@...>]

In lua baselib.c,it give us a lot of base function,such as:

static const struct luaL_reg iolib[] = {
  {LUA_ERRORMESSAGE, errorfb},
  {"clock",     io_clock},
  {"date",     io_date},
  {"debug",    io_debug},
  {"execute",  io_execute},
  {"exit",     io_exit},
  {"getenv",   io_getenv},
  {"remove",   io_remove},
  {"rename",   io_rename},
  {"setlocale", setloc},
  {"tmpname",   io_tmpname}
};

static const struct luaL_reg iolibtag[] = {
  {"appendto", io_appendto},
  {"closefile",   io_close},
  {"flush",     io_flush},
  {"openfile",   io_open},
  {"read",     io_read},
  {"readfrom", io_readfrom},
  {"seek",     io_seek},
  {"write",    io_write},
  {"writeto",  io_writeto}
};

and in my project,I definded a lot of function of myself.and register to lua.

in Lua script,I can use this function:

test.lua


function main()
  print("hello wolrd");
end function

main();

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I use the function by its funciton name:"print",How can I call print function,not by its function name,but use the index of the function in the array?