#14172: GHC hangs during type-checking -------------------------------------+------------------------------------- Reporter: lightandlight | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.2 Resolution: | Keywords: Operating System: Linux | Architecture: x86_64 Type of failure: Compile-time | (amd64) crash or panic | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): Seems to work OK with HEAD. What about with 8.2? With HEAD I get {{{ T14172.hs:7:19: error: • Occurs check: cannot construct the infinite type: a ~ g'1 a Expected type: (f'0 a -> f (f'0 b)) -> Compose f'0 g'1 a -> f (h a') Actual type: (Unwrapped (Compose f'0 g'1 a) -> f (Unwrapped (h a'))) -> Compose f'0 g'1 a -> f (h a') • In the first argument of ‘(.)’, namely ‘_Wrapping Compose’ In the expression: _Wrapping Compose . traverse In an equation for ‘traverseCompose’: traverseCompose = _Wrapping Compose . traverse • Relevant bindings include traverseCompose :: (a -> f b) -> g a -> f (h a') (bound at T14172.hs:7:1) | 7 | traverseCompose = _Wrapping Compose . traverse | ^^^^^^^^^^^^^^^^^ T14172.hs:7:19: error: • Couldn't match type ‘g’ with ‘Compose f'0 g'1’ ‘g’ is a rigid type variable bound by the inferred type of traverseCompose :: (a -> f b) -> g a -> f (h a') at T14172.hs:7:1-46 Expected type: (a -> f b) -> g a -> f (h a') Actual type: (a -> f b) -> Compose f'0 g'1 a -> f (h a') • In the expression: _Wrapping Compose . traverse In an equation for ‘traverseCompose’: traverseCompose = _Wrapping Compose . traverse • Relevant bindings include traverseCompose :: (a -> f b) -> g a -> f (h a') (bound at T14172.hs:7:1) | 7 | traverseCompose = _Wrapping Compose . traverse | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14172#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler