Re: [GHC] #13035: GHC enters a loop when partial type signatures and advanced type level code mix

29 Dec 2016

      #13035: GHC enters a loop when partial type signatures and advanced type level code
mix
-------------------------------------+-------------------------------------
        Reporter:  xcmw              |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by xcmw):

 For some reason this similar code works fine. The only change I made was
 creating and using NutritionW.

 {{{
 {-# LANGUAGE PolyKinds, DataKinds, TypeOperators, TypeFamilies, GADTs,
 PartialTypeSignatures, UndecidableInstances #-}

 newtype MyAttr a b = MyAttr { _unMyAttr :: MyFun (a b) }
 type MyRec a b = Rec (MyAttr a) b

 type family MyFun (a :: k1) :: k2

 data GY (a :: k1) (b :: k2) (c :: k1 -> k3) (d :: k1)
 data GNone (a :: k1)

 type family GYTF a where
     GYTF (GY a b _ a) = b
     GYTF (GY _ _ c d) = MyFun (c d)

 type instance MyFun (GY a b c d) = GYTF (GY a b c d)

 type family GNoneTF (a :: k1) :: k2 where

 type instance MyFun (GNone a) = GNoneTF a

 type (a :: k1) =: (b :: k2) = a `GY` b
 type (a :: j1 -> j2) $ (b :: j1) = a b

 infixr 0 $
 infixr 9 =:

 data FConst (a :: *) (b :: Fields)
 data FApply (a :: * -> * -> *) b c (d :: Fields)
 data FMap (a :: * -> *) b (d :: Fields)

 type instance MyFun (FConst a b) = a
 type instance MyFun (FApply b c d a) = b (MyFun (c a)) (MyFun (d a))
 type instance MyFun (FMap b c a) = b (MyFun (c a))

 data Fields = Name
             | Author
             | Image
             | Description
             | Ingredients
             | Instructions
             | CookTime
             | PrepTime
             | TotalTime
             | Yield
             | Nutrition
             | Tags
             | Url
             | Section
             | Items
             | Subsections
             | Calories
             | Carbohydrates
             | Cholesterol
             | Fat
             | Fiber
             | Protien
             | SaturatedFat
             | Sodium
             | Sugar
             | TransFat
             | UnsaturatedFat
             | ServingSize

 data Rec :: (u -> *) -> [u] -> * where
   RNil :: Rec f '[]
   (:&) :: !(f r) -> !(Rec f rs) -> Rec f (r ': rs)

 data family Sing (a :: k)
 data instance Sing (z_a6bn :: Fields)
       = z_a6bn ~ Name => SName |
         z_a6bn ~ Author => SAuthor |
         z_a6bn ~ Image => SImage |
         z_a6bn ~ Description => SDescription |
         z_a6bn ~ Ingredients => SIngredients |
         z_a6bn ~ Instructions => SInstructions |
         z_a6bn ~ CookTime => SCookTime |
         z_a6bn ~ PrepTime => SPrepTime |
         z_a6bn ~ TotalTime => STotalTime |
         z_a6bn ~ Yield => SYield |
         z_a6bn ~ Nutrition => SNutrition |
         z_a6bn ~ Tags => STags |
         z_a6bn ~ Url => SUrl |
         z_a6bn ~ Section => SSection |
         z_a6bn ~ Items => SItems |
         z_a6bn ~ Subsections => SSubsections |
         z_a6bn ~ Calories => SCalories |
         z_a6bn ~ Carbohydrates => SCarbohydrates |
         z_a6bn ~ Cholesterol => SCholesterol |
         z_a6bn ~ Fat => SFat |
         z_a6bn ~ Fiber => SFiber |
         z_a6bn ~ Protien => SProtien |
         z_a6bn ~ SaturatedFat => SSaturatedFat |
         z_a6bn ~ Sodium => SSodium |
         z_a6bn ~ Sugar => SSugar |
         z_a6bn ~ TransFat => STransFat |
         z_a6bn ~ UnsaturatedFat => SUnsaturatedFat |
         z_a6bn ~ ServingSize => SServingSize

 (=::) :: sing f -> MyFun (a f) -> MyAttr a f
 _ =:: x = MyAttr x

 type NutritionT
     = Calories       =: Maybe Int
     $ Carbohydrates  =: Maybe Int
     $ Cholesterol    =: Maybe Int
     $ Fat            =: Maybe Int
     $ Fiber          =: Maybe Int
     $ Protien        =: Maybe Int
     $ SaturatedFat   =: Maybe Int
     $ Sodium         =: Maybe Int
     $ Sugar          =: Maybe Int
     $ TransFat       =: Maybe Int
     $ UnsaturatedFat =: Maybe Int
     $ ServingSize    =: String
     $ GNone

 data NutritionW (x :: Fields)

 type instance MyFun (NutritionW x) = MyFun (NutritionT x)

 type NutritionRec = MyRec NutritionW ['Calories, 'Carbohydrates,
 'Cholesterol, 'Fat, 'Fiber, 'Protien, 'SaturatedFat, 'Sodium, 'Sugar,
 'TransFat, 'UnsaturatedFat, 'ServingSize]

 type RecipeT
     = Name         =: String
     $ Author       =: String
     $ Image        =: String
     $ Description  =: String
     $ CookTime     =: Maybe Int
     $ PrepTime     =: Maybe Int
     $ TotalTime    =: Maybe Int
     $ Yield        =: String
     $ Nutrition    =: NutritionRec
     $ Tags         =: [String]
     $ Url          =: String
     $ GNone

 type RecipeFormatter = FApply (->) (FConst [String]) (FMap IO RecipeT)

 g :: MyRec RecipeFormatter _ --'[ 'Author ] Uncomment to prevent loop
 g
      = SAuthor =:: (\a -> return "Hi")
     :& RNil

 main = putStrLn "Hi"
 }}}

--
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13035#comment:4
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