[Git][ghc/ghc][master] Predicate, Equivalence derive via `.. -> a -> All'
Marge Bot
gitlab at gitlab.haskell.org
Thu May 14 00:03:02 UTC 2020
Marge Bot pushed to branch master at Glasgow Haskell Compiler / GHC
Commits:
55e35c0b by Baldur Blöndal at 2020-05-13T20:02:48-04:00
Predicate, Equivalence derive via `.. -> a -> All'
- - - - -
1 changed file:
- libraries/base/Data/Functor/Contravariant.hs
Changes:
=====================================
libraries/base/Data/Functor/Contravariant.hs
=====================================
@@ -1,5 +1,8 @@
+{-# LANGUAGE DerivingStrategies #-}
+{-# LANGUAGE DerivingVia #-}
{-# LANGUAGE EmptyCase #-}
{-# LANGUAGE GeneralizedNewtypeDeriving #-}
+{-# LANGUAGE InstanceSigs #-}
{-# LANGUAGE StandaloneDeriving #-}
{-# LANGUAGE Trustworthy #-}
{-# LANGUAGE TypeOperators #-}
@@ -53,11 +56,11 @@ import Data.Functor.Product
import Data.Functor.Sum
import Data.Functor.Compose
-import Data.Monoid (Alt(..))
+import Data.Monoid (Alt(..), All(..))
import Data.Proxy
import GHC.Generics
-import Prelude hiding ((.),id)
+import Prelude hiding ((.), id)
-- | The class of contravariant functors.
--
@@ -76,6 +79,7 @@ import Prelude hiding ((.),id)
-- newtype Predicate a = Predicate { getPredicate :: a -> Bool }
--
-- instance Contravariant Predicate where
+-- contramap :: (a' -> a) -> (Predicate a -> Predicate a')
-- contramap f (Predicate p) = Predicate (p . f)
-- | `- First, map the input...
-- `----- then apply the predicate.
@@ -86,7 +90,7 @@ import Prelude hiding ((.),id)
--
-- Any instance should be subject to the following laws:
--
--- [Identity] @'contramap' 'id' = 'id'@
+-- [Identity] @'contramap' 'id' = 'id'@
-- [Composition] @'contramap' (g . f) = 'contramap' f . 'contramap' g@
--
-- Note, that the second law follows from the free theorem of the type of
@@ -94,7 +98,7 @@ import Prelude hiding ((.),id)
-- condition holds.
class Contravariant f where
- contramap :: (a -> b) -> f b -> f a
+ contramap :: (a' -> a) -> (f a -> f a')
-- | Replace all locations in the output with the same value.
-- The default definition is @'contramap' . 'const'@, but this may be
@@ -110,7 +114,7 @@ class Contravariant f where
-- lawful we have the following laws:
--
-- @
--- 'fmap' f ≡ 'phantom'
+-- 'fmap' f ≡ 'phantom'
-- 'contramap' f ≡ 'phantom'
-- @
phantom :: (Functor f, Contravariant f) => f a -> f b
@@ -123,79 +127,134 @@ infixl 4 >$, $<, >$<, >$$<
($<) = flip (>$)
-- | This is an infix alias for 'contramap'.
-(>$<) :: Contravariant f => (a -> b) -> f b -> f a
+(>$<) :: Contravariant f => (a -> b) -> (f b -> f a)
(>$<) = contramap
-- | This is an infix version of 'contramap' with the arguments flipped.
(>$$<) :: Contravariant f => f b -> (a -> b) -> f a
(>$$<) = flip contramap
-deriving instance Contravariant f => Contravariant (Alt f)
-deriving instance Contravariant f => Contravariant (Rec1 f)
-deriving instance Contravariant f => Contravariant (M1 i c f)
+deriving newtype instance Contravariant f => Contravariant (Alt f)
+deriving newtype instance Contravariant f => Contravariant (Rec1 f)
+deriving newtype instance Contravariant f => Contravariant (M1 i c f)
instance Contravariant V1 where
+ contramap :: (a' -> a) -> (V1 a -> V1 a')
contramap _ x = case x of
instance Contravariant U1 where
+ contramap :: (a' -> a) -> (U1 a -> U1 a')
contramap _ _ = U1
instance Contravariant (K1 i c) where
+ contramap :: (a' -> a) -> (K1 i c a -> K1 i c a')
contramap _ (K1 c) = K1 c
instance (Contravariant f, Contravariant g) => Contravariant (f :*: g) where
+ contramap :: (a' -> a) -> ((f :*: g) a -> (f :*: g) a')
contramap f (xs :*: ys) = contramap f xs :*: contramap f ys
instance (Functor f, Contravariant g) => Contravariant (f :.: g) where
+ contramap :: (a' -> a) -> ((f :.: g) a -> (f :.: g) a')
contramap f (Comp1 fg) = Comp1 (fmap (contramap f) fg)
instance (Contravariant f, Contravariant g) => Contravariant (f :+: g) where
+ contramap :: (a' -> a) -> ((f :+: g) a -> (f :+: g) a')
contramap f (L1 xs) = L1 (contramap f xs)
contramap f (R1 ys) = R1 (contramap f ys)
instance (Contravariant f, Contravariant g) => Contravariant (Sum f g) where
+ contramap :: (a' -> a) -> (Sum f g a -> Sum f g a')
contramap f (InL xs) = InL (contramap f xs)
contramap f (InR ys) = InR (contramap f ys)
instance (Contravariant f, Contravariant g)
- => Contravariant (Product f g) where
- contramap f (Pair a b) = Pair (contramap f a) (contramap f b)
+ => Contravariant (Product f g) where
+ contramap :: (a' -> a) -> (Product f g a -> Product f g a')
+ contramap f (Pair a b) = Pair (contramap f a) (contramap f b)
instance Contravariant (Const a) where
+ contramap :: (b' -> b) -> (Const a b -> Const a b')
contramap _ (Const a) = Const a
instance (Functor f, Contravariant g) => Contravariant (Compose f g) where
+ contramap :: (a' -> a) -> (Compose f g a -> Compose f g a')
contramap f (Compose fga) = Compose (fmap (contramap f) fga)
instance Contravariant Proxy where
+ contramap :: (a' -> a) -> (Proxy a -> Proxy a')
contramap _ _ = Proxy
newtype Predicate a = Predicate { getPredicate :: a -> Bool }
-
--- | A 'Predicate' is a 'Contravariant' 'Functor', because 'contramap' can
--- apply its function argument to the input of the predicate.
-instance Contravariant Predicate where
- contramap f g = Predicate $ getPredicate g . f
-
-instance Semigroup (Predicate a) where
- Predicate p <> Predicate q = Predicate $ \a -> p a && q a
-
-instance Monoid (Predicate a) where
- mempty = Predicate $ const True
+ deriving
+ ( -- | @('<>')@ on predicates uses logical conjunction @('&&')@ on
+ -- the results. Without newtypes this equals @'liftA2' (&&)@.
+ --
+ -- @
+ -- (<>) :: Predicate a -> Predicate a -> Predicate a
+ -- Predicate pred <> Predicate pred' = Predicate \a ->
+ -- pred a && pred' a
+ -- @
+ Semigroup
+ , -- | @'mempty'@ on predicates always returns @True at . Without
+ -- newtypes this equals @'pure' True at .
+ --
+ -- @
+ -- mempty :: Predicate a
+ -- mempty = \_ -> True
+ -- @
+ Monoid
+ )
+ via a -> All
+
+ deriving
+ ( -- | A 'Predicate' is a 'Contravariant' 'Functor', because
+ -- 'contramap' can apply its function argument to the input of
+ -- the predicate.
+ --
+ -- Without newtypes @'contramap' f@ equals precomposing with @f@
+ -- (= @(. f)@).
+ --
+ -- @
+ -- contramap :: (a' -> a) -> (Predicate a -> Predicate a')
+ -- contramap f (Predicate g) = Predicate (g . f)
+ -- @
+ Contravariant
+ )
+ via Op Bool
-- | Defines a total ordering on a type as per 'compare'.
--
-- This condition is not checked by the types. You must ensure that the
-- supplied values are valid total orderings yourself.
newtype Comparison a = Comparison { getComparison :: a -> a -> Ordering }
-
-deriving instance Semigroup (Comparison a)
-deriving instance Monoid (Comparison a)
+ deriving
+ newtype
+ ( -- | @('<>')@ on comparisons combines results with @('<>')
+ -- \@Ordering at . Without newtypes this equals @'liftA2' ('liftA2'
+ -- ('<>'))@.
+ --
+ -- @
+ -- (<>) :: Comparison a -> Comparison a -> Comparison a
+ -- Comparison cmp <> Comparison cmp' = Comparison \a a' ->
+ -- cmp a a' <> cmp a a'
+ -- @
+ Semigroup
+ , -- | @'mempty'@ on comparisons always returns @EQ at . Without
+ -- newtypes this equals @'pure' ('pure' EQ)@.
+ --
+ -- @
+ -- mempty :: Comparison a
+ -- mempty = Comparison \_ _ -> EQ
+ -- @
+ Monoid
+ )
-- | A 'Comparison' is a 'Contravariant' 'Functor', because 'contramap' can
-- apply its function argument to each input of the comparison function.
instance Contravariant Comparison where
- contramap f g = Comparison $ on (getComparison g) f
+ contramap :: (a' -> a) -> (Comparison a -> Comparison a')
+ contramap f (Comparison g) = Comparison (on g f)
-- | Compare using 'compare'.
defaultComparison :: Ord a => Comparison a
@@ -214,18 +273,34 @@ defaultComparison = Comparison compare
-- The types alone do not enforce these laws, so you'll have to check them
-- yourself.
newtype Equivalence a = Equivalence { getEquivalence :: a -> a -> Bool }
+ deriving
+ ( -- | @('<>')@ on equivalences uses logical conjunction @('&&')@
+ -- on the results. Without newtypes this equals @'liftA2'
+ -- ('liftA2' (&&))@.
+ --
+ -- @
+ -- (<>) :: Equivalence a -> Equivalence a -> Equivalence a
+ -- Equivalence equiv <> Equivalence equiv' = Equivalence \a b ->
+ -- equiv a b && equiv a b
+ -- @
+ Semigroup
+ , -- | @'mempty'@ on equivalences always returns @True at . Without
+ -- newtypes this equals @'pure' ('pure' True)@.
+ --
+ -- @
+ -- mempty :: Equivalence a
+ -- mempty = Equivalence \_ _ -> True
+ -- @
+ Monoid
+ )
+ via a -> a -> All
-- | Equivalence relations are 'Contravariant', because you can
-- apply the contramapped function to each input to the equivalence
-- relation.
instance Contravariant Equivalence where
- contramap f g = Equivalence $ on (getEquivalence g) f
-
-instance Semigroup (Equivalence a) where
- Equivalence p <> Equivalence q = Equivalence $ \a b -> p a b && q a b
-
-instance Monoid (Equivalence a) where
- mempty = Equivalence (\_ _ -> True)
+ contramap :: (a' -> a) -> (Equivalence a -> Equivalence a')
+ contramap f (Equivalence g) = Equivalence (on g f)
-- | Check for equivalence with '=='.
--
@@ -238,15 +313,36 @@ comparisonEquivalence (Comparison p) = Equivalence $ \a b -> p a b == EQ
-- | Dual function arrows.
newtype Op a b = Op { getOp :: b -> a }
-
-deriving instance Semigroup a => Semigroup (Op a b)
-deriving instance Monoid a => Monoid (Op a b)
+ deriving
+ newtype
+ ( -- | @('<>') \@(Op a b)@ without newtypes is @('<>') \@(b->a)@ =
+ -- @liftA2 ('<>')@. This lifts the 'Semigroup' operation
+ -- @('<>')@ over the output of @a at .
+ --
+ -- @
+ -- (<>) :: Op a b -> Op a b -> Op a b
+ -- Op f <> Op g = Op \a -> f a <> g a
+ -- @
+ Semigroup
+ , -- | @'mempty' \@(Op a b)@ without newtypes is @mempty \@(b->a)@
+ -- = @\_ -> mempty at .
+ --
+ -- @
+ -- mempty :: Op a b
+ -- mempty = Op \_ -> mempty
+ -- @
+ Monoid
+ )
instance Category Op where
+ id :: Op a a
id = Op id
+
+ (.) :: Op b c -> Op a b -> Op a c
Op f . Op g = Op (g . f)
instance Contravariant (Op a) where
+ contramap :: (b' -> b) -> (Op a b -> Op a b')
contramap f g = Op (getOp g . f)
instance Num a => Num (Op a b) where
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/55e35c0b7e0f4b907dc21d42827b1cea4317226e
--
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/55e35c0b7e0f4b907dc21d42827b1cea4317226e
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