#9151: Recursive default associated types don't kind-generalize properly -------------------------------------+------------------------------------ Reporter: goldfire | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Unknown/Multiple Type of failure: None/Unknown | Difficulty: Unknown Test Case: | Blocked By: Blocking: | Related Tickets: -------------------------------------+------------------------------------ Changes (by archblob): * cc: simonpj (added) Comment: I'm adding simonpj, maybe he can chime in. I'm writing again as documentation. I've been looking into the result of the dependency analysis done in `depAnalTyClDecls` and we have : {{{ REC type TEHelper = ToEnum Int class PEnum (k :: a) where type family ToEnum (x :: a) :: * type instance ToEnum x = TEHelper }}} which means we will try to check `TEHelper` before we generalize `ToEnum` and hence the kind check error. Braking the cycle and having: {{{ REC class PEnum (k :: a) where type family ToEnum (x :: a) :: * type instance ToEnum x = TEHelper NOREC type TEHelper = ToEnum Int }}} will only work if we defer default type instance checking as you suggested. These modifications have to go together. But they really fell hackish. One other thing that I don't know if we can do is somehow accommodate for this by tweaking the four steps in `kcTyClGroup` , I'll be looking into how to do that as an alternative and compare the two. Am I making sense ? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9151#comment:11 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler