#10534: Data families + Coercible = unsafeCoerce -------------------------------------+------------------------------------- Reporter: goldfire | Owner: Type: bug | Status: new Priority: highest | Milestone: 7.10.2 Component: Compiler | Version: 7.10.2-rc1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Blocked By: Test Case: | Related Tickets: Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- When I say {{{ {-# LANGUAGE TypeFamilies, FlexibleContexts #-} module A where import Data.Coerce data family DF a silly :: Coercible (DF a) (DF b) => a -> b silly = coerce }}} {{{ {-# LANGUAGE TypeFamilies #-} module B where import A newtype instance DF a = MkDF () unsafeCoerce :: a -> b unsafeCoerce = silly }}} I get {{{ [1 of 2] Compiling A ( A.hs, interpreted ) [2 of 2] Compiling B ( B.hs, interpreted ) Ok, modules loaded: A, B. }}} Eep! Happily, the fix is very very simple: `TyCon.isDistinctAlgRhs` should return `False` for `DataFamilyTyCon`s. This fix is already in-flight for HEAD in Phab:D968, but this ticket serves to correct this problem in 7.10.2 before the release. Patch coming very shortly. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10534 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler