{-# LANGUAGE AllowAmbiguousTypes #-} {-# LANGUAGE BangPatterns #-} {-# LANGUAGE ConstraintKinds #-} {-# LANGUAGE CPP #-} {-# LANGUAGE DataKinds #-} {-# LANGUAGE FlexibleContexts #-} {-# LANGUAGE FlexibleInstances #-} {-# LANGUAGE GADTs #-} {-# LANGUAGE MultiParamTypeClasses #-} {-# LANGUAGE PolyKinds #-} {-# LANGUAGE RankNTypes #-} {-# LANGUAGE ScopedTypeVariables #-} {-# LANGUAGE TypeApplications #-} {-# LANGUAGE TypeFamilies #-} {-# LANGUAGE TypeOperators #-} {-# LANGUAGE UndecidableInstances #-} -- | Core vinyl definitions. The 'Rec' data type is defined here, but -- also of interest are definitions commonly used functions like -- 'rmap', 'rapply', and 'rtraverse'. -- -- The definitions in this module are written in terms of type classes -- so that the definitions may be specialized to each record type at -- which they are used. This usually helps with runtime performance, -- but can slow down compilation time. If you are experiencing poor -- compile times, you may wish to try the semantically equivalent -- definitions in the "Data.Vinyl.Recursive" module: they should -- produce the same results given the same inputs as functions defined -- in this module, but they will not be specialized to your record -- type. Instead, they treat the record as a list of fields, so will -- have performance linear in the size of the record. module Data.Vinyl.Core where import Data.Monoid (Monoid) #if __GLASGOW_HASKELL__ < 804 import Data.Semigroup (Semigroup(..)) #endif import Foreign.Ptr (castPtr, plusPtr) import Foreign.Storable (Storable(..)) import Data.Functor.Product (Product(Pair)) import Data.List (intercalate) import Data.Vinyl.Functor import Data.Vinyl.TypeLevel import Data.Type.Equality (TestEquality (..), (:~:) (..)) import Data.Type.Coercion (TestCoercion (..), Coercion (..)) import GHC.Generics import GHC.Types (Constraint, Type) -- | A record is parameterized by a universe @u@, an interpretation @f@ and a -- list of rows @rs@. The labels or indices of the record are given by -- inhabitants of the kind @u@; the type of values at any label @r :: u@ is -- given by its interpretation @f r :: *@. data Rec :: (u -> *) -> [u] -> * where RNil :: Rec f '[] (:&) :: !(f r) -> !(Rec f rs) -> Rec f (r ': rs) infixr 7 :& infixr 5 <+> infixl 8 <<$>> infixl 8 <<*>> instance TestEquality f => TestEquality (Rec f) where testEquality RNil RNil = Just Refl testEquality (x :& xs) (y :& ys) = do Refl <- testEquality x y Refl <- testEquality xs ys Just Refl testEquality _ _ = Nothing instance TestCoercion f => TestCoercion (Rec f) where testCoercion RNil RNil = Just Coercion testCoercion (x :& xs) (y :& ys) = do Coercion <- testCoercion x y Coercion <- testCoercion xs ys Just Coercion testCoercion _ _ = Nothing -- | Two records may be pasted together. rappend :: Rec f as -> Rec f bs -> Rec f (as ++ bs) rappend RNil ys = ys rappend (x :& xs) ys = x :& (xs `rappend` ys) -- | A shorthand for 'rappend'. (<+>) :: Rec f as -> Rec f bs -> Rec f (as ++ bs) (<+>) = rappend -- | Combine two records by combining their fields using the given -- function. The first argument is a binary operation for combining -- two values (e.g. '(<>)'), the second argument takes a record field -- into the type equipped with the desired operation, the third -- argument takes the combined value back to a result type. rcombine :: (RMap rs, RApply rs) => (forall a. m a -> m a -> m a) -> (forall a. f a -> m a) -> (forall a. m a -> g a) -> Rec f rs -> Rec f rs -> Rec g rs rcombine smash toM fromM x y = rmap fromM (rapply (rmap (Lift . smash) x') y') where x' = rmap toM x y' = rmap toM y -- | 'Rec' @_ rs@ with labels in kind @u@ gives rise to a functor @Hask^u -> -- Hask@; that is, a natural transformation between two interpretation functors -- @f,g@ may be used to transport a value from 'Rec' @f rs@ to 'Rec' @g rs@. class RMap rs where rmap :: (forall x. f x -> g x) -> Rec f rs -> Rec g rs instance RMap '[] where rmap _ RNil = RNil {-# INLINE rmap #-} instance RMap xs => RMap (x ': xs) where rmap f (x :& xs) = f x :& rmap f xs {-# INLINE rmap #-} -- | A shorthand for 'rmap'. (<<$>>) :: RMap rs => (forall x. f x -> g x) -> Rec f rs -> Rec g rs (<<$>>) = rmap {-# INLINE (<<$>>) #-} -- | An inverted shorthand for 'rmap'. (<<&>>) :: RMap rs => Rec f rs -> (forall x. f x -> g x) -> Rec g rs xs <<&>> f = rmap f xs {-# INLINE (<<&>>) #-} -- | A record of components @f r -> g r@ may be applied to a record of @f@ to -- get a record of @g@. class RApply rs where rapply :: Rec (Lift (->) f g) rs -> Rec f rs -> Rec g rs instance RApply '[] where rapply _ RNil = RNil {-# INLINE rapply #-} instance RApply xs => RApply (x ': xs) where rapply (f :& fs) (x :& xs) = getLift f x :& (fs `rapply` xs) {-# INLINE rapply #-} -- | A shorthand for 'rapply'. (<<*>>) :: RApply rs => Rec (Lift (->) f g) rs -> Rec f rs -> Rec g rs (<<*>>) = rapply {-# INLINE (<<*>>) #-} -- | Given a section of some functor, records in that functor of any size are -- inhabited. class RecApplicative rs where rpure :: (forall x. f x) -> Rec f rs instance RecApplicative '[] where rpure _ = RNil {-# INLINE rpure #-} instance RecApplicative rs => RecApplicative (r ': rs) where rpure s = s :& rpure s {-# INLINE rpure #-} -- | A record may be traversed with respect to its interpretation functor. This -- can be used to yank (some or all) effects from the fields of the record to -- the outside of the record. rtraverse :: Applicative h => (forall x. f x -> h (g x)) -> Rec f rs -> h (Rec g rs) rtraverse _ RNil = pure RNil rtraverse f (x :& xs) = (:&) <$> f x <*> rtraverse f xs {-# INLINABLE rtraverse #-} -- | While 'rtraverse' pulls the interpretation functor out of the -- record, 'rtraverseIn' pushes the interpretation functor in to each -- field type. This is particularly useful when you wish to discharge -- that interpretation on a per-field basis. For instance, rather than -- a @Rec IO '[a,b]@, you may wish to have a @Rec Identity '[IO a, IO -- b]@ so that you can evaluate a single field to obtain a value of -- type @Rec Identity '[a, IO b]@. rtraverseIn :: forall h f g rs. (forall a. f a -> g (ApplyToField h a)) -> Rec f rs -> Rec g (MapTyCon h rs) rtraverseIn _ RNil = RNil rtraverseIn f (x :& xs) = f x :& rtraverseIn f xs {-# INLINABLE rtraverseIn #-} -- | Push an outer layer of interpretation functor into each field. rsequenceIn :: forall f g (rs :: [Type]). (Traversable f, Applicative g) => Rec (f :. g) rs -> Rec g (MapTyCon f rs) rsequenceIn = rtraverseIn @f (sequenceA . getCompose) {-# INLINABLE rsequenceIn #-} -- | Given a natural transformation from the product of @f@ and @g@ to @h@, we -- have a natural transformation from the product of @'Rec' f@ and @'Rec' g@ to -- @'Rec' h@. You can also think about this operation as zipping two records -- with the same element types but different interpretations. rzipWith :: (RMap xs, RApply xs) => (forall x. f x -> g x -> h x) -> Rec f xs -> Rec g xs -> Rec h xs rzipWith f = rapply . rmap (Lift . f) -- | Map each element of a record to a monoid and combine the results. class RFoldMap rs where rfoldMapAux :: Monoid m => (forall x. f x -> m) -> m -> Rec f rs -> m instance RFoldMap '[] where rfoldMapAux _ m RNil = m {-# INLINE rfoldMapAux #-} instance RFoldMap xs => RFoldMap (x ': xs) where rfoldMapAux f m (r :& rs) = rfoldMapAux f (mappend m (f r)) rs {-# INLINE rfoldMapAux #-} rfoldMap :: forall rs m f. (Monoid m, RFoldMap rs) => (forall x. f x -> m) -> Rec f rs -> m rfoldMap f = rfoldMapAux f mempty {-# INLINE rfoldMap #-} -- | A record with uniform fields may be turned into a list. class RecordToList rs where recordToList :: Rec (Const a) rs -> [a] instance RecordToList '[] where recordToList RNil = [] {-# INLINE recordToList #-} instance RecordToList xs => RecordToList (x ': xs) where recordToList (x :& xs) = getConst x : recordToList xs {-# INLINE recordToList #-} -- | Wrap up a value with a capability given by its type data Dict c a where Dict :: c a => a -> Dict c a -- | Sometimes we may know something for /all/ fields of a record, but when -- you expect to be able to /each/ of the fields, you are then out of luck. -- Surely given @∀x:u.φ(x)@ we should be able to recover @x:u ⊢ φ(x)@! Sadly, -- the constraint solver is not quite smart enough to realize this and we must -- make it patently obvious by reifying the constraint pointwise with proof. class ReifyConstraint c f rs where reifyConstraint :: Rec f rs -> Rec (Dict c :. f) rs instance ReifyConstraint c f '[] where reifyConstraint RNil = RNil {-# INLINE reifyConstraint #-} instance (c (f x), ReifyConstraint c f xs) => ReifyConstraint c f (x ': xs) where reifyConstraint (x :& xs) = Compose (Dict x) :& reifyConstraint xs {-# INLINE reifyConstraint #-} -- | Build a record whose elements are derived solely from a -- constraint satisfied by each. class RPureConstrained c ts where rpureConstrained :: (forall a. c a => f a) -> Rec f ts instance RPureConstrained c '[] where rpureConstrained _ = RNil {-# INLINE rpureConstrained #-} instance (c x, RPureConstrained c xs) => RPureConstrained c (x ': xs) where rpureConstrained f = f :& rpureConstrained @c @xs f {-# INLINE rpureConstrained #-} -- | Capture a type class instance dictionary. See -- 'Data.Vinyl.Lens.getDict' for a way to obtain a 'DictOnly' value -- from an 'RPureConstrained' constraint. data DictOnly (c :: k -> Constraint) a where DictOnly :: forall c a. c a => DictOnly c a -- | A useful technique is to use 'rmap (Pair (DictOnly @MyClass))' on -- a 'Rec' to pair each field with a type class dictionary for -- @MyClass@. This helper can then be used to eliminate the original. withPairedDict :: (c a => f a -> r) -> Product (DictOnly c) f a -> r withPairedDict f (Pair DictOnly x) = f x -- | Build a record whose elements are derived solely from a -- list of constraint constructors satisfied by each. class RPureConstraints cs ts where rpureConstraints :: (forall a. AllSatisfied cs a => f a) -> Rec f ts instance RPureConstraints cs '[] where rpureConstraints _ = RNil {-# INLINE rpureConstraints #-} instance (AllSatisfied cs t, RPureConstraints cs ts) => RPureConstraints cs (t ': ts) where rpureConstraints f = f :& rpureConstraints @cs @ts f {-# INLINE rpureConstraints #-} -- | Records may be shown insofar as their points may be shown. -- 'reifyConstraint' is used to great effect here. instance (RMap rs, ReifyConstraint Show f rs, RecordToList rs) => Show (Rec f rs) where show xs = (\str -> "{" <> str <> "}") . intercalate ", " . recordToList . rmap (\(Compose (Dict x)) -> Const $ show x) $ reifyConstraint @Show xs instance Semigroup (Rec f '[]) where RNil <> RNil = RNil instance (Semigroup (f r), Semigroup (Rec f rs)) => Semigroup (Rec f (r ': rs)) where (x :& xs) <> (y :& ys) = (x <> y) :& (xs <> ys) instance Monoid (Rec f '[]) where mempty = RNil RNil `mappend` RNil = RNil instance (Monoid (f r), Monoid (Rec f rs)) => Monoid (Rec f (r ': rs)) where mempty = mempty :& mempty (x :& xs) `mappend` (y :& ys) = (mappend x y) :& (mappend xs ys) instance Eq (Rec f '[]) where _ == _ = True instance (Eq (f r), Eq (Rec f rs)) => Eq (Rec f (r ': rs)) where (x :& xs) == (y :& ys) = (x == y) && (xs == ys) instance Ord (Rec f '[]) where compare _ _ = EQ instance (Ord (f r), Ord (Rec f rs)) => Ord (Rec f (r ': rs)) where compare (x :& xs) (y :& ys) = mappend (compare x y) (compare xs ys) instance Storable (Rec f '[]) where sizeOf _ = 0 alignment _ = 0 peek _ = return RNil poke _ RNil = return () instance (Storable (f r), Storable (Rec f rs)) => Storable (Rec f (r ': rs)) where sizeOf _ = sizeOf (undefined :: f r) + sizeOf (undefined :: Rec f rs) {-# INLINE sizeOf #-} alignment _ = alignment (undefined :: f r) {-# INLINE alignment #-} peek ptr = do !x <- peek (castPtr ptr) !xs <- peek (ptr `plusPtr` sizeOf (undefined :: f r)) return $ x :& xs {-# INLINE peek #-} poke ptr (!x :& xs) = poke (castPtr ptr) x >> poke (ptr `plusPtr` sizeOf (undefined :: f r)) xs {-# INLINE poke #-} instance Generic (Rec f '[]) where type Rep (Rec f '[]) = C1 ('MetaCons "RNil" 'PrefixI 'False) (S1 ('MetaSel 'Nothing 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) U1) from RNil = M1 (M1 U1) to (M1 (M1 U1)) = RNil instance (Generic (Rec f rs)) => Generic (Rec f (r ': rs)) where type Rep (Rec f (r ': rs)) = C1 ('MetaCons ":&" ('InfixI 'RightAssociative 7) 'False) (S1 ('MetaSel 'Nothing 'NoSourceUnpackedness 'SourceStrict 'DecidedStrict) (Rec0 (f r)) :*: S1 ('MetaSel 'Nothing 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rep (Rec f rs))) from (x :& xs) = M1 (M1 (K1 x) :*: M1 (from xs)) to (M1 (M1 (K1 x) :*: M1 xs)) = x :& to xs