Hi all, My goal is to compose Kleisli arrows with (State s) as parameteric Monadic type. So, I end up with the following code: data REnv :: [*] -> * -> * -> (* -> * -> *) -> ((* -> *) -> * -> * -> *) -> * where Last :: k (s t) i o -> REnv (t ': '[]) i o s k RCons :: k (s t) i o' -> REnv ts o' o s k -> REnv (t ': ts) i o s k Which, of course, gives me the following error when I try to play with it: *H> :t Last genRanking <interactive>:1:6: Kind incompatibility when matching types: s :: * -> * -> * StateT Ranking :: (* -> *) -> * -> * Expected type: Kleisli (s t) Ticket Ranking Actual type: Kleisli (State Ranking) Ticket Ranking In the first argument of ‘Last’, namely ‘genRanking’ In the expression: Last genRanking <interactive>:1:6: Kind incompatibility when matching types: t :: * Data.Functor.Identity.Identity :: * -> * Expected type: Kleisli (s t) Ticket Ranking Actual type: Kleisli (State Ranking) Ticket Ranking In the first argument of ‘Last’, namely ‘genRanking’ In the expression: Last genRanking*H> :t LastLast :: k (s t) i o -> REnv '[t] i o s k*H> :t genRanking genRanking :: Kleisli (State Ranking) Ticket Ranking I understand why it fails (State is * -> * -> *, while s is * -> *), but I can't figure out how to write this, I tried (s t o), but it isn't correct because k waits for a (* -> *). If you have any ideas, I'm curious to read them. Thanks in advance for your help.