{-# LANGUAGE CPP #-}
{- | Description: Data instances
'Data.Data.Data' instances for 'HListFlat' and 'Record' which pretend
to be flat data structures. The @Data@ instance for 'HList' gives a nested
structure.
NOTE: these instances do not work with ghc-7.8 with promoted
string (Symbol) labels because of
[@HList@]
The data instance for
> a :: HList '[Int, Double, b]
Looks like the same instance for
> type T b = (Int, (Double, (b, ())))
[@HListFlat@]
The Data instance for
> a :: Data b => HListFlat '[Int,Double,b]
will look like the Data instance for:
> data A b = A Int Double b
[@Record@]
For 'Record' similar ideas apply. An
> a :: Record '[ LVPair "x" Int, LVPair "y" Double ]
should behave like a:
> data A = A { x :: Int, y :: Double } deriving (Data)
Many unsafecoerces are necessary here because the Data class includes type
parameters @c@ that cannot be used in the class context for the instance.
Perhaps there is another way.
-}
module Data.HList.Data (
-- * exports for type signatures/ haddock usage
DataHListFlatCxt,
DataRecordCxt,
TypeRepsList(..),
-- ** less likely to be used
RecordLabelsStr(..),
GfoldlK(..),
GunfoldK(..),
HListFlat(..),
TypeablePolyK,
) where
import Data.HList.FakePrelude
import Data.HList.HList
import Data.HList.Record
import Data.HList.Variant
import GHC.TypeLits
import Data.Data
import Data.HList.TIC
import Data.HList.TIP
#if OLD_TYPEABLE
import Data.List
import GHC.Exts (Constraint)
#endif
import Unsafe.Coerce
deriving instance Data (HList '[])
deriving instance
(Data x,
Data (HList xs),
TypeablePolyK (x ': xs), -- for new typeable
Typeable (HList (x ': xs) -- for old typeable
)) => Data (HList (x ': xs))
deriving instance
(TypeablePolyK xs,
Typeable (HList xs),
Data (HList xs)) => Data (TIP xs)
deriving instance
(TypeablePolyK xs,
Typeable (Variant xs),
Data (Variant xs)) => Data (TIC xs)
-- | this data type only exists to have Data instance
newtype HListFlat a = HListFlat (HList a)
type DataHListFlatCxt g a = (HBuild' '[] g,
Typeable (HListFlat a),
TypeablePolyK a,
HFoldl (GfoldlK C) (C g) a (C (HList a)),
HFoldr
(GunfoldK C)
(C g)
(HReplicateR (HLength a) ())
(C (HList a)),
HReplicate (HLength a) ())
instance DataHListFlatCxt g a => Data (HListFlat a) where
gfoldl k z (HListFlat xs) = c3 $
hFoldl
(c1 (GfoldlK k))
(c2 (z hBuild))
xs
where
c1 :: forall c. GfoldlK c -> GfoldlK C
c1 = unsafeCoerce
c2 :: forall c. c g -> C g
c2 = unsafeCoerce
c3 :: forall c. C (HList a) -> c (HListFlat a)
c3 = unsafeCoerce
gunfold k z _ =
c3 $ withSelf $ \self ->
hFoldr
(c1 (GunfoldK k))
(c2 (z hBuild))
(hReplicate (hLength self) ())
where
withSelf :: forall t c. (t -> c t) -> c t
withSelf x = x undefined
c1 :: forall c. GunfoldK c -> GunfoldK C
c1 = unsafeCoerce
c2 :: forall c. c g -> C g
c2 = unsafeCoerce
c3 :: forall c. C (HList a) -> c (HListFlat a)
c3 = unsafeCoerce
dataTypeOf _ = hListFlatDataRep
toConstr _ = hListFlatConRep
hListFlatDataRep = mkDataType "Data.HList.HList" [hListFlatConRep]
hListFlatConRep = mkConstr hListFlatDataRep "HListFlat" [] Prefix
type DataRecordCxt a =
(Data (HListFlat (RecordValuesR a)),
TypeablePolyK a,
TypeRepsList (Record a),
RecordValues a,
RecordLabelsStr a)
instance DataRecordCxt a => Data (Record a) where
gfoldl k z xs = c1 (gfoldl k z (HListFlat (recordValues xs)))
where
c1 :: forall c. c (HListFlat (RecordValuesR a)) -> c (Record a)
c1 = unsafeCoerce
gunfold k z con = c1 (gunfold k z con)
where
-- LVPair and Record are newtypes, so this should be safe...
c1 :: forall c. c (HListFlat (RecordValuesR a)) -> c (Record a)
c1 = unsafeCoerce
dataTypeOf x = snd (recordReps (recordLabelsStr x))
toConstr x = fst (recordReps (recordLabelsStr x))
recordReps fields =
let c = mkConstr d "Record" fields Prefix
d = mkDataType "Data.HList.Record" [c]
in (c,d)
class RecordLabelsStr (xs :: [*]) where
recordLabelsStr :: Record xs -> [String]
instance RecordLabelsStr '[] where
recordLabelsStr _ = []
instance (RecordLabelsStr xs,
ShowLabel x) => RecordLabelsStr (Tagged x t ': xs) where
recordLabelsStr _ = showLabel (Label :: Label x) :
recordLabelsStr (undefined :: Record xs)
{- |
This alternative option works too, but for whatever reason
splitting up recordLabelsStr and recordLabels into two functions
means that a type annotation is needed on the 3, which is not
necessary with the above recordLabelsStr (ghc-7.6.3)
> recordLabelsStr2 (recordLabels (((Label :: Label "x") .=. 3 .*. emptyRecord )))
-}
class RecordLabelsStr2 (xs :: [k]) where
recordLabelsStr2 :: proxy xs -> [String]
instance RecordLabelsStr2 '[] where
recordLabelsStr2 _ = []
instance (RecordLabelsStr2 xs,
ShowLabel x) => RecordLabelsStr2 (x ': xs) where
recordLabelsStr2 _ = showLabel (Label :: Label x) :
recordLabelsStr2 (Proxy :: Proxy xs)
-- | use only with @instance Data (HList a)@. This is because the HFoldl
-- context cannot be written for a @c@ that only appears in the method
-- 'gfoldl'.
data C a
-- typeable isntances... either hand written or derived when possible
#if !OLD_TYPEABLE
deriving instance Typeable Record
deriving instance Typeable HList
deriving instance Typeable HListFlat
deriving instance Typeable Variant
deriving instance Typeable TIC
deriving instance Typeable TIP
-- orphans
deriving instance Typeable 'HZero
deriving instance Typeable 'HSucc
#if !MIN_VERSION_base(4,8,0)
-- GHC 7.9 adds these instances
deriving instance Typeable '[]
deriving instance Typeable '(:)
#endif
#else
instance TypeRepsList (Record xs) => Typeable (HList xs) where
typeOf x = mkTyConApp (mkTyCon3 "HList" "Data.HList.HList" "HList")
[ tyConList (typeRepsList (Record x)) ]
instance (TypeRepsList (Record xs)) => Typeable (Record xs) where
typeOf x = mkTyConApp (mkTyCon3 "HList" "Data.HList.Record" "Record")
[ tyConList (typeRepsList x) ]
instance TypeRepsList (Record xs) => Typeable (Variant xs) where
typeOf _ = mkTyConApp (mkTyCon3 "HList" "Data.HList.Variant" "Variant")
[ tyConList (typeRepsList (error "Data.HList.Data:Typeable Variant" :: Record xs)) ]
instance Typeable (Variant xs) => Typeable (TIC xs) where
typeOf (TIC xs) = mkTyConApp (mkTyCon3 "HList" "Data.HList.TIC" "TIC")
[typeOf xs]
instance Typeable (HList xs) => Typeable (TIP xs) where
typeOf (TIP xs) = mkTyConApp (mkTyCon3 "HList" "Data.HList.TIP" "TIP")
[typeOf xs]
instance ShowLabel sy => Typeable1 (Tagged sy) where
typeOf1 _ = mkTyConApp
(mkTyCon3 "HList" "Data.HList.Data" (showLabel (Label :: Label sy)))
[]
instance (ShowLabel sy, Typeable x) => Typeable (Tagged sy x) where
typeOf _ = mkTyConApp
(mkTyCon3 "GHC" "GHC.TypeLits" (showLabel (Label :: Label sy)))
[mkTyConApp (mkTyCon3 "HList" "Data.HList.Record" "=") [],
typeOf (error "Data.HList.Data:Typeable Tagged" :: x)
]
instance Typeable (HList a) => Typeable (HListFlat a) where
typeOf _ = mkTyConApp (mkTyCon3 "HList" "Data.HList.Data" "HListFlat")
[typeOf (error "Typeable HListFlat" :: HList a)]
-- pretty-prints sort of like a real list
tyConList xs = mkTyConApp open ( intersperse comma xs ++ [close] )
where
open = mkTyCon3 "GHC" "GHC.TypeLits" "["
close = mkTyConApp (mkTyCon3 "GHC" "GHC.TypeLits" "]") []
comma = mkTyConApp (mkTyCon3 "GHC" "GHC.TypeLits" ",") []
#endif
class TypeRepsList a where
typeRepsList :: a -> [TypeRep]
instance (TypeRepsList (HList xs)) => TypeRepsList (Record xs) where
typeRepsList (Record xs) = typeRepsList xs
instance (TypeRepsList (HList xs), Typeable x) => TypeRepsList (HList (x ': xs)) where
typeRepsList (~(x `HCons` xs))
= typeOf x : typeRepsList xs
instance TypeRepsList (HList '[]) where
typeRepsList _ = []
-- | wraps up the first argument to 'gfoldl'
data GfoldlK c where
GfoldlK :: (forall d b . Data d => c (d -> b) -> d -> c b) -> GfoldlK c
instance (Data d, (c (d -> b), d) ~ x, c b ~ y) =>
ApplyAB (GfoldlK c) x y where
applyAB (GfoldlK f) (u,v) = f u v
data GunfoldK c where
GunfoldK :: (forall b r. Data b => c (b -> r) -> c r) -> GunfoldK c
instance (Data b, x ~ (t, c (b -> r)), y ~ c r) =>
ApplyAB (GunfoldK c) x y where
applyAB (GunfoldK f) (_, u) = f u