#12522: GHC 8.0.1 hangs, looping forever in type-checker -------------------------------------+------------------------------------- Reporter: clinton | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple crash | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Description changed by clinton: @@ -5,3 +5,1 @@ - {-# LANGUAGE TypeFamilyDependencies #-} - {-# LANGUAGE FlexibleInstances #-} - {-# LANGUAGE AllowAmbiguousTypes #-} + {-# LANGUAGE TypeFamilyDependencies #-} @@ -9,1 +7,1 @@ - main = return $ f (Just 'c') + main = return $ f (Just 'c') @@ -11,2 +9,2 @@ - data D1 x - data D2 + data D1 x + data D2 @@ -14,3 +12,3 @@ - type family TF x = t | t -> x - type instance TF (D1 x, a) = Maybe (TF (x, a)) - type instance TF (D2, ()) = Char + type family TF x = t | t -> x + type instance TF (D1 x, a) = Maybe (TF (x, a)) + type instance TF (D2, ()) = Char @@ -18,2 +16,2 @@ - class C p where - f :: TF (x, a) -> () + f :: TF (x, a) -> () + f _ = () New description: I'm not sure if this is a bug or hanging the compiler is expected here. This was the minimal example that causes GHC to hang: {{{#!hs {-# LANGUAGE TypeFamilyDependencies #-} main = return $ f (Just 'c') data D1 x data D2 type family TF x = t | t -> x type instance TF (D1 x, a) = Maybe (TF (x, a)) type instance TF (D2, ()) = Char f :: TF (x, a) -> () f _ = () }}} -- -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12522#comment:6 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler