#13735: RankNTypes don't work with PatternSynonyms -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: bug | Status: closed Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Resolution: invalid | Keywords: | PatternSynonyms 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 Iceland_jack): Ah what confused me was that they both (''seemingly'') allow extracting a polymorphic function {{{#!hs type Id = forall xx. xx -> xx one :: A -> Id one (A f) = f two :: B -> Id two (B (Endo f)) = f }}} But this doesn't work: (like your `f2 (L (Lam x)) = (x 'c', x True)` example demonstrates) {{{#!hs -- works einn :: A -> (Int -> Int, () -> ()) einn (A f) = (f, f) -- fails tveir :: B -> (Int -> Int, () -> ()) tveir (B (Endo f)) = (f, f) }}} With your desugaring and #11350 {{{#!hs A (\@x -> id @x) B (\@x -> Endo @x (id @x)) }}} it becomes clearer to me. Thanks! -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13735#comment:7 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler