#10828: TH could do a better job of representing GADTs -------------------------------------+------------------------------------- Reporter: spinda | Owner: jstolarek Type: feature request | Status: new Priority: normal | Milestone: 8.0.1 Component: Template Haskell | Version: 7.10.2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by jstolarek): These are `Foldable` instances derived automatically for data types in comment:8 {{{#!hs instance Foldable T1 where foldr f z (MkT1 a1) = f a1 z foldMap f (MkT1 a1) = f a1 instance Foldable T1' where foldr f z (MkT1' a1) = f a1 z foldMap f (MkT1' a1) = f a1 instance Foldable T2 where foldr f z (MkT2 a1) = (\ b1 b2 -> b2) a1 z foldMap f (MkT2 a1) = (\ b1 -> mempty) a1 instance Foldable T2' where foldr f z (MkT2' a1) = (\ b1 b2 -> b2) a1 z foldMap f (MkT2' a1) = (\ b1 -> mempty) a1 instance Foldable T3 where foldr f z (MkT3 a1) = (\ b1 b2 -> b2) a1 z foldMap f (MkT3 a1) = (\ b1 -> mempty) a1 instance Foldable T3' where foldr f z (MkT3' a1) = (\ b1 b2 -> b2) a1 z foldMap f (MkT3' a1) = (\ b1 -> mempty) a1 }}} So `DerivingFoldable` does not distinguish between GADT and normal declarations - respective pairs of instances are identical. At least in this case. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10828#comment:15 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler