[GHC] #3476: Compiler warning about non-exhaustive pattern match with GADT and type-signature

[GHC]

#3476: Compiler warning about non-exhaustive pattern match with GADT and type-
signature
---------------------------+------------------------------------------------
Reporter:  Ashley Yakeley  |          Owner:                         
    Type:  bug             |         Status:  new                    
Priority:  normal          |      Component:  Compiler (Type checker)
 Version:  6.10.4          |       Severity:  normal                 
Keywords:                  |       Testcase:                         
      Os:  Linux           |   Architecture:  x86_64 (amd64)         
---------------------------+------------------------------------------------
 This program:
 {{{
 {-# OPTIONS -Wall #-}
 {-# LANGUAGE GADTs #-}
 module Bug where

     data T n where
         BoolT :: T Bool
         IntT :: T Int

     f :: T Bool -> Int
     f BoolT = 3
 }}}
 ...gives this warning
 {{{
 $ ghc -c Bug.hs

 Bug.hs:10:4:
     Warning: Pattern match(es) are non-exhaustive
              In the definition of `f': Patterns not matched: IntT
 }}}
 The pattern match is, in fact, exhaustive, given the type signature.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3476>
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