I started experiment with strict functors. I come to:
import Control.Exception import Foreign import Prelude hiding (catch)
data StrictMonad a = StrictMonad a deriving Show
instance Functor StrictMonad where f `fmap` StrictMonad v = return $ f v
instance Applicative StrictMonad where pure = return (<*>) = ap
instance Monad StrictMonad where return x = unsafePerformIO $ do (return $! x) `catch` \(SomeException _) -> return x return $! StrictMonad x StrictMonad v >>= f = f v
It seems to be valid IMHO Functor and Monad (I haven't prove it) as long as functions terminates. Some time ago there was post stating that there is not possible strict 'interesting' functor - I guess that the above is 'interesting' (and due to halting problem I guess it is not possible to create strict Functor which would deal with that problem). Regards