Eh, I'm playing fast and loose to validate a number of interesting things that come out of that blog post. The `FFI a` functor is just Yoneda of (F o = exists i

Eh, I'm playing fast and loose to validate a number of interesting things that come out of that blog post. The `FFI a` functor is just Yoneda of (F o = exists i . (FFI i o, i)) which you want because we can't guarantee that `FFI i` is a functor. You can form the standard free monad over (Yoneda F) just fine, but if you do it in the weird CPS style indicated here you get something that's faster in Haskell ("well, ok, so what") but also has a really nice story where the only remaining bit is "the interpreter is exactly giving semantics to FFI". It's also nice to do parallel threads in this way, but it's not infeasible to do them with the standard free formation. Totally just aesthetics. I'll see if I can dig up an example of two concurrent threads interacting over a shared flipflop. Also worth thinking about a definition of FFI which goes like data FFI i o where Unsafe :: (i -> o) -> FFI i o C :: (Storable i, Storable o) => String -> FFI i o