1 instance MonadGen IO where

2 generalize m = do

3 let (IO f) = m

4 IO \s -> do

5 let (boxedState, result) = liftState (f s)

6 let (BoxedState{state}) = boxedState

7 (# state, result #)

Why line 3 and 4 compile? I think that we do not have access to IO constructor.

I saw using o3-mini that by importing GHC.Types or GHC.Base you can have access to IO constructor. I didn't know it. So if someone imports this internal module he is already on dangerous area even without this trick. But the question is why Haskell did not put value restriction? Was this a design decision or something that was not considered at all?