#3927: Incomplete/overlapped pattern warnings + GADTs = inadequate -------------------------------------+------------------------------------ Reporter: simonpj | Owner: simonpj Type: bug | Status: new Priority: high | Milestone: 7.8.3 Component: Compiler | Version: 6.12.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Unknown/Multiple Type of failure: None/Unknown | Difficulty: Unknown Test Case: | Blocked By: Blocking: | Related Tickets: #4139 -------------------------------------+------------------------------------ Comment (by cactus): I was asked about the following program failing to compile. Do you think this is also caused by the same underlying problem? {{{ {-# OPTIONS_GHC -fwarn-incomplete-patterns -Werror #-} {-# LANGUAGE GADTs, TypeFamilies #-} type family F a type instance F a = () data Foo a where FooA :: Foo () FooB :: Foo Int f :: a -> Foo (F a) -> () f _ FooA = () }}} The error/warning is, of course: {{{ gadt-incomplete.hs:12:1: Warning: Pattern match(es) are non-exhaustive In an equation for `f': Patterns not matched: _ FooB }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/3927#comment:31 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler