#12990: Partially applied constructors with unpacked fields simplified badly -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Runtime | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by dfeuer): Actually, I guess the eta-expansion per se is always safe (because a strict constructor can never have a weird arity), and will lead to case- of-known-constructor when relevant. I don't have any opinion whatsoever about exactly ''how'' this should be fixed; I just want it fixed. I've had to write some unpleasantly long-winded code in `containers` to work around this. It shows up all over `Traversable` things, for instance. {{{#!hs data Node = Node2 !Int a a | Node3 !Int a a a instance Traversable Node where traverse f (Node2 sz x y) = Node2 sz <$> traverse f x <*> traverse f y ... }}} is no good; GHC would box up the node size (which starts out unboxed!) just to put it in the closure passed to `fmap`. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12990#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler