#8674: User output should not show eta-contracted data instances ------------------------------------+------------------------------------- Reporter: simonpj | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.6.3 Keywords: | Operating System: Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: None/Unknown Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | ------------------------------------+------------------------------------- Consider {{{ data family Sing (a :: k) data instance Sing (a :: [k]) = SNil data instance Sing Bool = SBool }}} If you load this into ghci and say `:info Sing` you get {{{ :i Sing type role Sing nominal data family Sing (a :: k) -- Defined at T8557.hs:4:1 data instance Sing Bool -- Defined at T8557.hs:6:15 data instance Sing -- Defined at T8557.hs:5:15 }}} The `data instance` is eta-contracted (see `Note [Eta reduction for data family axioms]` in `TcInstDcls`). This is jolly confusing for our users. We should eta-expand before displaying. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8674 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler