#8968: Pattern synonyms and GADTs ----------------------------------------------+---------------------------- Reporter: kosmikus | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler (Type checker) | Version: Resolution: | 7.8.1-rc2 Operating System: Unknown/Multiple | Keywords: Type of failure: GHC rejects valid program | Architecture: Test Case: | Unknown/Multiple Blocking: | Difficulty: Unknown | Blocked By: | Related Tickets: ----------------------------------------------+---------------------------- Comment (by cactus): We don't have frontend support for pattern synonym signatures (see #8584). However, this can be worked around using the technique described in #8584, so I was able to get your code to typecheck by modifying it as: {{{ {-# LANGUAGE GADTs, KindSignatures, PatternSynonyms, ScopedTypeVariables #-} data X :: (* -> *) -> * -> * where Y :: f Int -> X f Int pattern C x = (Y (Just x) :: X Maybe Int) }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8968#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler