[GHC] #13673: Core lint error with defer-typed-holes

9 May 2017


      #13673: Core lint error with defer-typed-holes
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           Reporter:  Iceland_jack   |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.0.1
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 Another Core Lint error

 {{{#!hs
 {-# Options_GHC -dcore-lint -fdefer-typed-holes #-}

 {-# Language ViewPatterns, PatternSynonyms, GeneralizedNewtypeDeriving,
 DeriveTraversable #-}

 import Data.Bifunctor.Fix
 import Data.Bifunctor.Tannen
 import Test.QuickCheck
 import Test.QuickCheck.Function
 import Control.Applicative

 newtype ZL a = ZL { getZL :: Fix (Tannen Maybe (,)) a }
   deriving (Eq, Ord, Read, Show, Functor, Applicative, Foldable,
 Traversable)

 fromList :: [a] -> ZL a
 fromList []     = Nil
 fromList (x:xs) = x:::fromList xs

 pattern Nil :: ZL a
 pattern Nil = ZL (In (Tannen Nothing))

 foo :: ZL a -> Maybe (a, ZL a)
 foo (ZL (In (Tannen (Just (as, a))))) = Just (a, ZL as)

 infixr 5 :::
 pattern (:::) :: a -> ZL a -> ZL a
 pattern a:::as   <- ZL (In (Tannen (Just (ZL -> as, a))))
   where a:::ZL as = ZL (In (Tannen (Just (as, a))))

 u (Fn f) as bs = let
   (xs, ys) = (ZipList as, ZipList bs)

   in getZipList (liftA2 f xs ys) == toList (liftA2 f (fromList as)
 (fromList bs))
 }}}

 unfortunately I don't have time to reduce it

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Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13673
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