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>> You have to store Lua value of a function in a registry with
>> luaL_ref(). Store integer that luaL_ref() returns.
>> When callback is called, it should be called with that integer. Fetch
>> stored value from registry and call it.
>> When you no longer need to store the value of function (in general
>> this is not the same moment as the function is called), you remove its
>> value from the registry.

>> I would post some code this evening.

> I thought I'd use luaL_ref, keep a struct for callback information.  But I
> was missing another bit of information.  luaL_ref() pops a value off the
> stack but I'm not popping the stack, just looping through it.   So do I need
> to change my loop to pop or do some dance to move the function to the top of
> the stack pop it using luaL_ref() then put it back where it was?

Use lua_pushvalue() to push value already on stack.

> Anyway, I look forward to the code later.  Back to less interesting stuff at
> work.

Something along these lines (pseudocode). Tell me (off the list) if
you need actually working code.

static void get_value_from_lua(lua_State *L, int index)
  t = lua_type(L, index);
  switch (t)
    case LUA_TFUNCTION: /* function */
      // What to save here so lua_callback() function to call.
luaL_ref? lua_topointer?
      // setup callback
      lua_pushvalue(L, index);
      int ref = luaL_ref(L, LUA_REGISTRYINDEX);
      /* store int somewhere*/

/* How you get EXTRA_ARGS depends on the implementation */
static int lua_callback(lua_State * L, int ref, EXTRA_ARGS)
  lua_rawgeti(L, ref); /* push stored function */
  int nargs = /* Number of EXTRA_ARGS */;
  /* ...push EXTRA_ARGS to stack... */
  /* call function (error checking omitted) */
  lua_pcall(L, nargs,  LUA_MULTRET);
  /* Process results */

static int collect_callback(lua_State * L, int ref)
   lua_unref(L, ref);