#10928: Refine pattern synonym signatures -------------------------------------+------------------------------------- Reporter: mpickering | Owner: Type: bug | Status: new Priority: normal | Milestone: 8.0.1 Component: Compiler | Version: 7.10.2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: Other | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): -------------------------------------+------------------------------------- Comment (by rwbarton): I'm actually coming around to the original syntax, but with the constraints reversed as in comment:5. It's not so bad and it can be extended to support required values too, using an empty provided constraint if needed. {{{ pattern IsMember :: Ord a => a -> () => Set a pattern IsMember val <- (member val -> True) pattern Lookup :: Ord k => k -> () => v -> Map k v pattern Lookup key val <- (lookup key -> Just val) }}} I have to say writing these pattern signatures was a bit mind-bending, but I don't think that's because of the particular concrete syntax involving constraints. I still feel that maybe we ought to be able to do better, but I consider this solution at least satisfactory. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10928#comment:13 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler