[Git][ghc/ghc][master] Make Functor a quantified superclass of Bifunctor.
Marge Bot (@marge-bot)
gitlab at gitlab.haskell.org
Thu Dec 1 17:36:07 UTC 2022
Marge Bot pushed to branch master at Glasgow Haskell Compiler / GHC
Commits:
d87f28d8 by Baldur Blöndal at 2022-11-30T21:16:36+01:00
Make Functor a quantified superclass of Bifunctor.
See https://github.com/haskell/core-libraries-committee/issues/91 for
discussion.
This change relates Bifunctor with Functor by requiring second = fmap.
Moreover this change is a step towards unblocking the major version bump
of bifunctors and profunctors to major version 6. This paves the way to
move the Profunctor class into base. For that Functor first similarly
becomes a superclass of Profunctor in the new major version 6.
- - - - -
8 changed files:
- compiler/GHC/Data/Graph/Inductive/PatriciaTree.hs
- libraries/base/Data/Bifunctor.hs
- libraries/base/GHC/Base.hs
- libraries/base/changelog.md
- testsuite/tests/deriving/should_compile/T9968a.hs
- testsuite/tests/deriving/should_compile/T9968a.stderr
- testsuite/tests/deriving/should_compile/deriving-via-compile.hs
- testsuite/tests/ghci/scripts/T12550.stdout
Changes:
=====================================
compiler/GHC/Data/Graph/Inductive/PatriciaTree.hs
=====================================
@@ -116,6 +116,9 @@ instance DynGraph Gr where
in Gr g3
+instance Functor (Gr a) where
+ fmap = fastEMap
+
instance Bifunctor Gr where
bimap = fastNEMap
=====================================
libraries/base/Data/Bifunctor.hs
=====================================
@@ -1,5 +1,6 @@
-{-# LANGUAGE Safe #-}
{-# LANGUAGE CPP #-}
+{-# LANGUAGE QuantifiedConstraints #-}
+{-# LANGUAGE Safe #-}
-----------------------------------------------------------------------------
-- |
@@ -39,7 +40,11 @@ import GHC.Generics ( K1(..) )
-- arguments are covariant.
--
-- You can define a 'Bifunctor' by either defining 'bimap' or by
--- defining both 'first' and 'second'.
+-- defining both 'first' and 'second'. A partially applied 'Bifunctor'
+-- must be a 'Functor' and the 'second' method must agree with 'fmap'.
+-- From this it follows that:
+--
+-- @'second' 'id' = 'id'@
--
-- If you supply 'bimap', you should ensure that:
--
@@ -64,8 +69,10 @@ import GHC.Generics ( K1(..) )
-- 'second' (f '.' g) ≡ 'second' f '.' 'second' g
-- @
--
+-- Since 4.18.0.0 'Functor' is a superclass of 'Bifunctor.
+--
-- @since 4.8.0.0
-class Bifunctor p where
+class (forall a. Functor (p a)) => Bifunctor p where
{-# MINIMAL bimap | first, second #-}
-- | Map over both arguments at the same time.
=====================================
libraries/base/GHC/Base.hs
=====================================
@@ -559,6 +559,18 @@ instance (Monoid a, Monoid b, Monoid c) => Applicative ((,,,) a b c) where
instance (Monoid a, Monoid b, Monoid c) => Monad ((,,,) a b c) where
(u, v, w, a) >>= k = case k a of (u', v', w', b) -> (u <> u', v <> v', w <> w', b)
+-- | @since 4.18.0.0
+instance Functor ((,,,,) a b c d) where
+ fmap f (a, b, c, d, e) = (a, b, c, d, f e)
+
+-- | @since 4.18.0.0
+instance Functor ((,,,,,) a b c d e) where
+ fmap fun (a, b, c, d, e, f) = (a, b, c, d, e, fun f)
+
+-- | @since 4.18.0.0
+instance Functor ((,,,,,,) a b c d e f) where
+ fmap fun (a, b, c, d, e, f, g) = (a, b, c, d, e, f, fun g)
+
-- | @since 4.10.0.0
instance Semigroup a => Semigroup (IO a) where
(<>) = liftA2 (<>)
=====================================
libraries/base/changelog.md
=====================================
@@ -1,7 +1,9 @@
# Changelog for [`base` package](http://hackage.haskell.org/package/base)
## 4.18.0.0 *TBA*
-
+ * Add `forall a. Functor (p a)` superclass for `Bifunctor p`.
+ * Add Functor instances for `(,,,,) a b c d`, `(,,,,,) a b c d e` and
+ `(,,,,,) a b c d e f`.
* Exceptions thrown by weak pointer finalizers are now reported via a global
exception handler.
* Add `GHC.Weak.Finalize.{get,set}FinalizerExceptionHandler` which the user to
=====================================
testsuite/tests/deriving/should_compile/T9968a.hs
=====================================
@@ -5,4 +5,4 @@ module T9968 where
import Data.Bifunctor
data Blah a b = A a | B b
- deriving (Bifunctor)
+ deriving (Functor, Bifunctor)
=====================================
testsuite/tests/deriving/should_compile/T9968a.stderr
=====================================
@@ -1,5 +1,5 @@
-T9968a.hs:8:13: warning: [GHC-06201] [-Wmissing-methods (in -Wdefault)]
+T9968a.hs:8:22: warning: [GHC-06201] [-Wmissing-methods (in -Wdefault)]
• No explicit implementation for
either ‘bimap’ or (‘first’ and ‘second’)
• In the instance declaration for ‘Bifunctor Blah’
=====================================
testsuite/tests/deriving/should_compile/deriving-via-compile.hs
=====================================
@@ -308,7 +308,7 @@ instance Biapplicative (,) where
(f a b, f' a' b')
newtype WrapBiapp p a b = WrapBiap (p a b)
- deriving newtype (Bifunctor, Biapplicative, Eq)
+ deriving newtype (Functor, Bifunctor, Biapplicative, Eq)
instance (Biapplicative p, Num a, Num b) => Num (WrapBiapp p a b) where
(+) = biliftA2 (+) (+)
=====================================
testsuite/tests/ghci/scripts/T12550.stdout
=====================================
@@ -26,6 +26,12 @@ class Functor f where
instance ∀ a. Functor ((,) a) -- Defined in ‘GHC.Base’
instance ∀ a b. Functor ((,,) a b) -- Defined in ‘GHC.Base’
instance ∀ a b c. Functor ((,,,) a b c) -- Defined in ‘GHC.Base’
+instance ∀ a b c d. Functor ((,,,,) a b c d)
+ -- Defined in ‘GHC.Base’
+instance ∀ a b c d e. Functor ((,,,,,) a b c d e)
+ -- Defined in ‘GHC.Base’
+instance ∀ a b c d e f. Functor ((,,,,,,) a b c d e f)
+ -- Defined in ‘GHC.Base’
instance ∀ r. Functor ((->) r) -- Defined in ‘GHC.Base’
instance Functor IO -- Defined in ‘GHC.Base’
instance Functor [] -- Defined in ‘GHC.Base’
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/d87f28d810b9c536ca4db7f363163e6d0dd6c93c
--
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/d87f28d810b9c536ca4db7f363163e6d0dd6c93c
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