[GHC] #7649: BangPatterns + ViewPatterns

[GHC]

#7649: BangPatterns + ViewPatterns
---------------------------------+------------------------------------------
    Reporter:  igloo             |       Owner:                  
        Type:  bug               |      Status:  new             
    Priority:  normal            |   Milestone:                  
   Component:  Compiler          |     Version:  7.7             
    Keywords:                    |          Os:  Unknown/Multiple
Architecture:  Unknown/Multiple  |     Failure:  None/Unknown    
  Difficulty:  Unknown           |    Testcase:                  
   Blockedby:                    |    Blocking:                  
     Related:                    |  
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 This program:
 {{{
 {-# LANGUAGE ViewPatterns, BangPatterns #-}

 import Control.Exception

 main :: IO ()
 main = do print (f False)
           print (f True)
           print (g undefined) `catchE` \_ -> putStrLn "g exception"
           print (h undefined) `catchE` \_ -> putStrLn "h exception"
           print (i undefined) `catchE` \_ -> putStrLn "i exception"
           putStrLn "Done"

 f :: Bool -> String
 f (view -> Nothing) = "Got Nothing"
 f (view -> Just x)  = "Got Just " ++ show x

 g :: Bool -> String
 g (view -> x) = "g Got something"

 h :: Bool -> String
 h (view -> !x) = "h Got something"

 i :: Bool -> String
 i !(view -> x) = "i Got something"

 view :: Bool -> Maybe Int
 view False = Nothing
 view True = Just 5

 catchE :: IO a -> (ErrorCall -> IO a) -> IO a
 catchE = catch
 }}}
 prints:
 {{{
 "Got Nothing"
 "Got Just 5"
 "g Got something"
 "h exception
 "i Got something"
 Done
 }}}
 but presumably `i` ought to be strict in `x`.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7649>
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