#8779: Exhaustiveness checks for pattern synonyms -------------------------------------+------------------------------------- Reporter: nomeata | Owner: mpickering Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler (Type | Version: 7.8.1 checker) | Keywords: Resolution: | PatternSynonyms Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D2669 Wiki Page: | -------------------------------------+------------------------------------- Comment (by mpickering): To respond to an earlier point that Reid and others have made. The potential problems with this pragma only highlight design compromises with pattern synonyms. The specific issue being that pattern synonyms are ad- hoc collections rather than a complete set of covering patterns. Reid's suggestion of improving exhaustiveness checking by seeing if the view function is injective is akin to suggesting that one should only be allowed to define complete sets of pattern synonyms in the first place. I see the design I have implemented as the sensible way of doing so. If we forced all users to write pattern synonyms in the way that Reid described then we would have been better off implementing views! -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8779#comment:45 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler