#13768: Incorrect warnings generated by exhaustiveness checker with pattern synonyms / GADT combination -------------------------------------+------------------------------------- Reporter: kosmikus | Owner: (none) Type: bug | Status: new Priority: high | Milestone: Component: Compiler | Version: 8.2.1-rc2 Resolution: | 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 Simon Peyton Jones <simonpj@…>): In [changeset:"6b77914cd37b697354611bcd87897885c1e5b4a6/ghc" 6b77914/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="6b77914cd37b697354611bcd87897885c1e5b4a6" Fix instantiation of pattern synonyms In Check.hs (pattern match ovelap checking) we to figure out the instantiation of a pattern synonym from the type of the pattern. We were doing this utterly wrongly. Trac #13768 demonstrated this bogosity. The fix is easy; and is described in PatSyn.hs Note [Pattern synonym result type] }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13768#comment:2> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler