{-# LANGUAGE RankNTypes #-} ----------------------------------------------------------------------------- -- | -- Module : Control.Comonad.Hoist.Class -- Copyright : (C) 2008-2013 Edward Kmett -- License : BSD-style (see the file LICENSE) -- -- Maintainer : Edward Kmett <ekmett@gmail.com> -- Stability : provisional -- Portability : portable ---------------------------------------------------------------------------- module Control.Comonad.Hoist.Class ( ComonadHoist(cohoist) ) where import Control.Comonad import Control.Monad.Trans.Identity class ComonadHoist t where -- | Given any comonad-homomorphism from @w@ to @v@ this yields a comonad -- homomorphism from @t w@ to @t v@. cohoist :: (Comonad w, Comonad v) => (forall x. w x -> v x) -> t w a -> t v a instance ComonadHoist IdentityT where cohoist l = IdentityT . l . runIdentityT {-# INLINE cohoist #-}