How are functions passed from the interpreter to the host?

[LukaHorvat]

So briefly what I'm trying to do is write a game in Haskell, and the engine I'm using requires me to build my code into a dll with takes ages on Windows. I want to speed up my iteration cycle so I thought I'd just compile the dll once and then dynamically interpret my Haskell scripts.

From the type level it seems I've managed to set everything up, my code compiles and runs, I can see the output. The issue is that the engine starts complaining that something internal isn't initialized when the interpreted code calls some of the engine API and I'm unsure why that is.

The way I'm doing it is that I have a ready :: EngineState -> IO () function in a separate module that uses the engine API on the EngineState. I interpret that module and pass the ready function back to the host with interpret "ready" (as :: EngineState -> IO ()). Then I call that function in the actually compiled part of my code.
Does this have any chance of working? What I thought was that maybe when I get this function back to the host, it's only a shim that marshals the inputs to the interpreter, then runs the code there and then marshals the results back. In that case it would make sense that things like internal MVars and whatnot don't survive the process. At least not with correct semantics.

The thing is, I've tried a simpler program that just sets the provided MVar and it's effects are indeed visible in the host so I'm not sure anymore.

[gelisam]

The interpreter is not a separate process, so there is no need to marshall anything. I'd expect both putMVar and ready to work as intended; I'm afraid you will have to dig deeper into the bowels of your engine in order to understand how it initializes things and checks whether things are initialized, because there isn't an obvious cause which comes to mind. If you can figure out what your engine does and reproduce the problem in a small standalone example, that will hopefully make the cause much clearer.

[LukaHorvat]

Hmm, weird. When I compile the module and call the function directly, it works. I'll have to look into it I guess.