#8016: case expression with mixed use of Num instances cause spurious overlap warning ----------------------------------------------+----------------------------- Reporter: bscarlet | Owner: Type: bug | Status: new Priority: normal | Component: Compiler Version: 7.6.3 | Keywords: case overlap Os: Unknown/Multiple | Architecture: Unknown/Multiple Failure: Incorrect warning at compile-time | Blockedby: Blocking: | Related: ----------------------------------------------+----------------------------- {{{ newtype Whomp = Whomp Int deriving (Eq) instance Num Whomp where Whomp a + Whomp b = Whomp (a+b) Whomp a * Whomp b = Whomp (a*b) abs (Whomp a) = Whomp (abs a) signum (Whomp a) = Whomp (signum a) fromInteger = Whomp . fromInteger foo :: Whomp -> String foo cc = case cc of Whomp 0 -> "zero" 10 -> "ten" }}} produces {{{ Foo.hs:12:10: Warning: Pattern match(es) are overlapped In a case alternative: Whomp 0 -> ... }}} -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/8016 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler