#4185: Deriving higher-arity instances for newtype family instances fails ---------------------------------+------------------------------------------ Reporter: LouisWasserman | Owner: simonpj Type: bug | Status: new Priority: low | Milestone: 7.6.2 Component: Compiler | Version: 6.12.3 Keywords: | Os: Unknown/Multiple Architecture: Unknown/Multiple | Failure: None/Unknown Difficulty: | Testcase: Blockedby: | Blocking: Related: | ---------------------------------+------------------------------------------ Comment(by sjoerd_visscher): DeriveFunctor has the same problem: {{{ data family D x :: * -> * data instance D () a = X a deriving Functor }}} gives {{{ Derived instance `Functor (D ())' requires illegal partial application of data type family D In the data instance declaration for `D' }}} While implementing the instance by hand works fine: {{{ instance Functor (D ()) where fmap f (X a) = X (f a) }}} -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/4185#comment:7 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler