#9892: Decomposition of AppTy broken -------------------------------------+------------------------------------- Reporter: simonpj | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.3 Keywords: | Operating System: Architecture: Unknown/Multiple | Unknown/Multiple Difficulty: Unknown | Type of failure: Blocked By: | None/Unknown Related Tickets: | Test Case: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- This program (taken from `lens`) wrongly fails in GHC's HEAD {{{ {-# LANGUAGE UndecidableInstances #-} import Control.Applicative import Control.Category import Prelude hiding ((.),id) newtype FocusingPlus w k s a = FocusingPlus { unfocusingPlus :: k (s, w) a } instance Functor (k (s, w)) => Functor (FocusingPlus w k s) where fmap f (FocusingPlus as) = FocusingPlus (fmap f as) instance Applicative (k (s, w)) => Applicative (FocusingPlus w k s) where pure = FocusingPlus . pure FocusingPlus kf <*> FocusingPlus ka = FocusingPlus (kf <*> ka) }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9892> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler