diff options
Diffstat (limited to 'libraries/base/Data/Functor/Classes.hs')
| -rw-r--r-- | libraries/base/Data/Functor/Classes.hs | 79 |
1 files changed, 71 insertions, 8 deletions
diff --git a/libraries/base/Data/Functor/Classes.hs b/libraries/base/Data/Functor/Classes.hs index e547dd12ad..92f3f89e1e 100644 --- a/libraries/base/Data/Functor/Classes.hs +++ b/libraries/base/Data/Functor/Classes.hs @@ -1,7 +1,10 @@ {-# LANGUAGE FlexibleContexts #-} +{-# LANGUAGE DefaultSignatures #-} {-# LANGUAGE InstanceSigs #-} {-# LANGUAGE Safe #-} +{-# LANGUAGE TypeOperators #-} {-# LANGUAGE UndecidableInstances #-} +{-# LANGUAGE QuantifiedConstraints #-} ----------------------------------------------------------------------------- -- | -- Module : Data.Functor.Classes @@ -91,8 +94,18 @@ import Text.Show (showListWith) -- | Lifting of the 'Eq' class to unary type constructors. -- +-- Any instance should be subject to the following law that canonicity +-- is preserved: +-- +-- @liftEq (==)@ = @(==)@ +-- +-- This class therefore represents the generalization of 'Eq' by +-- decomposing its main method into a canonical lifting on a canonical +-- inner method, so that the lifting can be reused for other arguments +-- than the canonical one. +-- -- @since 4.9.0.0 -class Eq1 f where +class (forall a. Eq a => Eq (f a)) => Eq1 f where -- | Lift an equality test through the type constructor. -- -- The function will usually be applied to an equality function, @@ -102,6 +115,10 @@ class Eq1 f where -- -- @since 4.9.0.0 liftEq :: (a -> b -> Bool) -> f a -> f b -> Bool + default liftEq + :: (f ~ f' c, Eq2 f', Eq c) + => (a -> b -> Bool) -> f a -> f b -> Bool + liftEq = liftEq2 (==) -- | Lift the standard @('==')@ function through the type constructor. -- @@ -111,8 +128,18 @@ eq1 = liftEq (==) -- | Lifting of the 'Ord' class to unary type constructors. -- +-- Any instance should be subject to the following law that canonicity +-- is preserved: +-- +-- @liftCompare compare@ = 'compare' +-- +-- This class therefore represents the generalization of 'Ord' by +-- decomposing its main method into a canonical lifting on a canonical +-- inner method, so that the lifting can be reused for other arguments +-- than the canonical one. +-- -- @since 4.9.0.0 -class (Eq1 f) => Ord1 f where +class (Eq1 f, forall a. Ord a => Ord (f a)) => Ord1 f where -- | Lift a 'compare' function through the type constructor. -- -- The function will usually be applied to a comparison function, @@ -122,6 +149,10 @@ class (Eq1 f) => Ord1 f where -- -- @since 4.9.0.0 liftCompare :: (a -> b -> Ordering) -> f a -> f b -> Ordering + default liftCompare + :: (f ~ f' c, Ord2 f', Ord c) + => (a -> b -> Ordering) -> f a -> f b -> Ordering + liftCompare = liftCompare2 compare -- | Lift the standard 'compare' function through the type constructor. -- @@ -131,6 +162,22 @@ compare1 = liftCompare compare -- | Lifting of the 'Read' class to unary type constructors. -- +-- Any instance should be subject to the following laws that canonicity +-- is preserved: +-- +-- @liftReadsPrec readsPrec readList@ = 'readsPrec' +-- +-- @liftReadList readsPrec readList@ = 'readList' +-- +-- @liftReadPrec readPrec readListPrec@ = 'readPrec' +-- +-- @liftReadListPrec readPrec readListPrec@ = 'readListPrec' +-- +-- This class therefore represents the generalization of 'Read' by +-- decomposing it's methods into a canonical lifting on a canonical +-- inner method, so that the lifting can be reused for other arguments +-- than the canonical one. +-- -- Both 'liftReadsPrec' and 'liftReadPrec' exist to match the interface -- provided in the 'Read' type class, but it is recommended to implement -- 'Read1' instances using 'liftReadPrec' as opposed to 'liftReadsPrec', since @@ -145,7 +192,7 @@ compare1 = liftCompare compare -- For more information, refer to the documentation for the 'Read' class. -- -- @since 4.9.0.0 -class Read1 f where +class (forall a. Read a => Read (f a)) => Read1 f where {-# MINIMAL liftReadsPrec | liftReadPrec #-} -- | 'readsPrec' function for an application of the type constructor @@ -219,14 +266,30 @@ liftReadListPrecDefault rp rl = list (liftReadPrec rp rl) -- | Lifting of the 'Show' class to unary type constructors. -- +-- Any instance should be subject to the following laws that canonicity +-- is preserved: +-- +-- @liftShowsPrec showsPrec showList@ = 'showsPrec' +-- +-- @liftShowList showsPrec showList@ = 'showList' +-- +-- This class therefore represents the generalization of 'Show' by +-- decomposing it's methods into a canonical lifting on a canonical +-- inner method, so that the lifting can be reused for other arguments +-- than the canonical one. +-- -- @since 4.9.0.0 -class Show1 f where +class (forall a. Show a => Show (f a)) => Show1 f where -- | 'showsPrec' function for an application of the type constructor -- based on 'showsPrec' and 'showList' functions for the argument type. -- -- @since 4.9.0.0 liftShowsPrec :: (Int -> a -> ShowS) -> ([a] -> ShowS) -> Int -> f a -> ShowS + default liftShowsPrec + :: (f ~ f' b, Show2 f', Show b) + => (Int -> a -> ShowS) -> ([a] -> ShowS) -> Int -> f a -> ShowS + liftShowsPrec = liftShowsPrec2 showsPrec showList -- | 'showList' function for an application of the type constructor -- based on 'showsPrec' and 'showList' functions for the argument type. @@ -248,7 +311,7 @@ showsPrec1 = liftShowsPrec showsPrec showList -- | Lifting of the 'Eq' class to binary type constructors. -- -- @since 4.9.0.0 -class Eq2 f where +class (forall a. Eq a => Eq1 (f a)) => Eq2 f where -- | Lift equality tests through the type constructor. -- -- The function will usually be applied to equality functions, @@ -268,7 +331,7 @@ eq2 = liftEq2 (==) (==) -- | Lifting of the 'Ord' class to binary type constructors. -- -- @since 4.9.0.0 -class (Eq2 f) => Ord2 f where +class (Eq2 f, forall a. Ord a => Ord1 (f a)) => Ord2 f where -- | Lift 'compare' functions through the type constructor. -- -- The function will usually be applied to comparison functions, @@ -302,7 +365,7 @@ compare2 = liftCompare2 compare compare -- For more information, refer to the documentation for the 'Read' class. -- -- @since 4.9.0.0 -class Read2 f where +class (forall a. Read a => Read1 (f a)) => Read2 f where {-# MINIMAL liftReadsPrec2 | liftReadPrec2 #-} -- | 'readsPrec' function for an application of the type constructor @@ -385,7 +448,7 @@ liftReadListPrec2Default rp1 rl1 rp2 rl2 = list (liftReadPrec2 rp1 rl1 rp2 rl2) -- | Lifting of the 'Show' class to binary type constructors. -- -- @since 4.9.0.0 -class Show2 f where +class (forall a. Show a => Show1 (f a)) => Show2 f where -- | 'showsPrec' function for an application of the type constructor -- based on 'showsPrec' and 'showList' functions for the argument types. -- |