#9211: Untouchable type variable (regression from 7.6) -------------------------------------+------------------------------------ Reporter: simonpj | 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: -------------------------------------+------------------------------------ Comment (by oleg): My real examples are not that different from the one I posted. Here is one of the recent ones: {{{ unsafeLam :: (Applicative m, AppPermutable i, SSym repr, LamPure repr) => (forall j. (j ~ (->) (repr a))) => (i :. j) (repr a) -> (m :. (i :. j)) (repr b)) -> (m :. i) (repr (a->b)) }}} As you can see, I use the type equality constraint to give an abbreviation to a complex type that appears several times in a complex expression. In the above example, 'j' is used as an abbreviation for '(->) (repr a)' that occurs twice in a large type. OCaml has the convenient notation 'type as x -> x -> x' to give an abbreviation to a type. I was happy that I found something similar in Haskell. Alas, as this ticket shows, sometimes it doesn't work. I have fixed my problem by getting rid of the abbreviation. (Giving the local type annotation in the real case proved to be too messy. The compiler kept complaining and needing more and more annotations.) -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9211#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler