#11424: "Occurs check" not considered when reducing closed type families -------------------------------------+------------------------------------- Reporter: diatchki | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler (Type | Version: 8.1 checker) | Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): What if 'a' was instantiated with `Loopy Int` where {{{ type family Loop x type instance Loopy Int = [Loopy Int] }}} Now indeed if we see `Same (Loopy Int) [Loopy Int]` we could reduce it to `Int`. This is all very tiresome I know. It's discussed at some length in our "Closed type families" paper. If you can think of a better solution than what we propose there, we're all ears. Simon -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11424#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler