Try this paper<https://www.microsoft.com/en-us/research/publication/levity-polymorphism/> The function type constructor actually has type (->) :: forall (r1::RuntimeRep) (r2::RuntimeRep). TYPE r1 -> TYPE r2 -> TYPE LiftedRep But when it appears applied to two argument, thus ((->) r1 r2 t1 t2), we print it infix (t1 -> t2). So (-> 'GHC.Types.LiftedRep 'GHC.Types.LiftedRep thing thing) is the same as (thing -> thing). I cannot explain why it is being printed in that non-infix way, but your email doesn’t give enough context to know. I hope this helps a bit. Where did you look for information? I’d like to add pointers that would have been helpful to you. Simon From: Ranjit Jhala <jhala@cs.ucsd.edu> Sent: 24 April 2019 04:56 To: ghc-devs@haskell.org; Simon Peyton Jones <simonpj@microsoft.com> Subject: Puzzled by GHC.Types.LiftedRep Hi all, Consider the following program: ``` import Control.Arrow (second) import qualified Control.Monad.Trans.Reader as R myLocal :: (r -> r) -> R.ReaderT r m a -> R.ReaderT r m a myLocal = undefined foo :: (thing -> thing) -> R.ReaderT (d, thing) m a -> R.ReaderT (d, thing) m a foo arg = myLocal (second arg) ``` When compiled with GHC 8.6.4, I get the odd behavior that at the call `second arg`, the type of `arg` is just: thing -> thing but the *input* type of `second` (after applying the various type and dictionary parameters) is something that looks like while the *input* type of `second` (after the various type and dictionary applications etc.) is the mysterious (to me): (-> 'GHC.Types.LiftedRep 'GHC.Types.LiftedRep thing thing) Can someone explain or point me to some documentation or paper that describes what the above means? Specifically, how/why does GHC "equate" the two things above in order to consider the core well-formed? Many thanks in advance! - Ranjit.