I would like to handle the following code in Lua and C:
Let's say that I have C function named Foo that is bound to Lua. I call it like following in Lua script:
Foo(15, "bar", function(z) return 2 * z + 1 end)
On the C side, I retrieve the arguments and I can store the number and string in my structure. But what data type would I need to store the anonymous function? And how can I call it later?
You can't store a Lua function as a C data type, anymore than you can store a Lua table as a C data type.
What you can do is use the registry to store this value. The registry is a globally-available table to all C users for storing data. It's often a good idea to pick a single key for all of your code and put a table at that key. This table would contain the values you want to preserve. This will help reduce conflicts from other C code using the registry.
You can either leave the function somewhere in the stack or save it in registry or some other table with luaL_ref.
Generally, you don't store the function in a C variable. You leave it on the stack and call it with pcall(). Something like:
int l_Foo(lua_State *L)
{
lua_pop(L, 2); /* ignore the first two args */
/* (the function is now on top of the stack) */
lua_pushnumber(L, 2); /* push the number to pass as z */
lua_pcall(L, 1, 1, 0); /* call the function with 1 argument, expect 1 result */
lua_pop(L, 1); /* ignore the result */
}
I've left out some error checking for the sake of brevity, but see Programming in Lua for a more complete example and the Lua Reference Manual for more details about the functions.
This page may also be helpful: http://www.lua.org/pil/25.2.html
And this: http://www.luafaq.org/#T7.2
And it seems like it was answered here: how to callback a lua function from a c function
One way would be to do the work of anonymous function
on the lua side and pass the result of function to
FOO(int, char*, fun_result_type fun_result)
