Delete group class, the groups package should be used instead

Keep `Additive`, however. See ChangeLog for more details.

The version in the cabal file is bumped to remind whoever does the
future release that this is breaking change.

Closes #4.

Author: Ericson2314

ChangeLog.md

@@ -1,5 +1,20 @@
 # Revision history for patch
 
+## Unreleased
+
+* Remove the `split-these` flag.
+  We do not need it as we only use the `These` datatype which is provided in all versions.
+
+* Stop defining `Group`; `Group` from the `groups` package can be used instead.
+
+  Most of the instances are provided by `groups`, except the `Group
+  MonoidalMap` instance, which is not lawful.  `reflex` might provide it as an
+  orphan for backwards compat, temporarily, but it should eventually be removed
+  everywhere.
+
+* `Applicative` is still defined, because the `Abelian` from `groups` has too
+  stringent a constraint.
+
 ## 0.0.3.2
 
 * Update version bounds

patch.cabal

@@ -1,5 +1,5 @@
 Name: patch
-Version: 0.0.3.2
+Version: 0.1.0.0
 Synopsis: Data structures for describing changes to other data structures.
 Description:
   Data structures for describing changes to other data structures.
@@ -25,11 +25,6 @@ tested-with:
   GHC ==8.0.2 || ==8.2.2 || ==8.4.4 || ==8.6.5 || ==8.8.1
   GHCJS ==8.4
 
-flag split-these
-  description: Use split these/semialign packages
-  manual:      False
-  default:     True
-
 library
   hs-source-dirs: src
   default-language: Haskell2010
@@ -40,6 +35,7 @@ library
                , dependent-sum >= 0.6 && < 0.8
                , lens >= 4.7 && < 5
                , semigroupoids >= 4.0 && < 6
+               , these >= 0.4 && < 1.2
                , transformers >= 0.5.6.0 && < 0.6
                , witherable >= 0.3 && < 0.4
 
@@ -56,14 +52,6 @@ library
 
   ghc-options: -Wall -fwarn-redundant-constraints -fwarn-tabs
 
-  if flag(split-these)
-    build-depends: these >= 1 && <1.2
-                 , semialign >=1 && <1.2
-                 , monoidal-containers >= 0.6 && < 0.7
-  else
-    build-depends: these >= 0.4 && <0.9
-                 , monoidal-containers == 0.4.0.0
-
 test-suite hlint
   default-language: Haskell2010
   type: exitcode-stdio-1.0

src/Data/Patch.hs

@@ -1,8 +1,6 @@
 {-# LANGUAGE CPP #-}
-{-# LANGUAGE GeneralizedNewtypeDeriving #-}
-{-# LANGUAGE StandaloneDeriving #-}
-{-# LANGUAGE TypeFamilies #-}
 {-# LANGUAGE TypeOperators #-}
+{-# LANGUAGE TypeFamilies #-}
 -- |
 -- Module:
 --   Data.Patch
@@ -13,10 +11,8 @@ module Data.Patch
   , module X
   ) where
 
-import Control.Applicative
 import Data.Functor.Const (Const (..))
 import Data.Functor.Identity
-import Data.Map.Monoidal (MonoidalMap)
 import Data.Proxy
 #if !MIN_VERSION_base(4,11,0)
 import Data.Semigroup (Semigroup (..))
@@ -39,12 +35,6 @@ import Data.Patch.MapWithMove as X
   , unsafePatchMapWithMove
   )
 
--- | A 'Group' is a 'Monoid' where every element has an inverse.
-class (Semigroup q, Monoid q) => Group q where
-  negateG :: q -> q
-  (~~) :: q -> q -> q
-  r ~~ s = r <> negateG s
-
 -- | An 'Additive' 'Semigroup' is one where (<>) is commutative
 class Semigroup q => Additive q where
 
@@ -55,52 +45,27 @@ instance Additive p => Patch (AdditivePatch p) where
   type PatchTarget (AdditivePatch p) = p
   apply (AdditivePatch p) q = Just $ p <> q
 
-instance (Ord k, Group q) => Group (MonoidalMap k q) where
-  negateG = fmap negateG
-
-instance (Ord k, Additive q) => Additive (MonoidalMap k q)
-
 -- | Trivial group.
-instance Group () where
-  negateG _ = ()
-  _ ~~ _ = ()
 instance Additive ()
 
 -- | Product group.  A Pair of groups gives rise to a group
-instance (Group a, Group b) => Group (a, b) where
-  negateG (a, b) = (negateG a, negateG b)
-  (a, b) ~~ (c, d) = (a ~~ c, b ~~ d)
 instance (Additive a, Additive b) => Additive (a, b)
 
 -- See https://gitlab.haskell.org/ghc/ghc/issues/11135#note_111802 for the reason Compose is not also provided.
 -- Base does not define Monoid (Compose f g a) so this is the best we can
 -- really do for functor composition.
-instance Group (f (g a)) => Group ((f :.: g) a) where
-  negateG (Comp1 xs) = Comp1 (negateG xs)
-  Comp1 xs ~~ Comp1 ys = Comp1 (xs ~~ ys)
 instance Additive (f (g a)) => Additive ((f :.: g) a)
 
 -- | Product of groups, Functor style.
-instance (Group (f a), Group (g a)) => Group ((f :*: g) a) where
-  negateG (a :*: b) = negateG a :*: negateG b
-  (a :*: b) ~~ (c :*: d) = (a ~~ c) :*: (b ~~ d)
 instance (Additive (f a), Additive (g a)) => Additive ((f :*: g) a)
 
 -- | Trivial group, Functor style
-instance Group (Proxy x) where
-  negateG _ = Proxy
-  _ ~~ _ = Proxy
 instance Additive (Proxy x)
 
 -- | Const lifts groups into a functor.
-deriving instance Group a => Group (Const a x)
 instance Additive a => Additive (Const a x)
 -- | Ideitnty lifts groups pointwise (at only one point)
-deriving instance Group a => Group (Identity a)
 instance Additive a => Additive (Identity a)
 
 -- | Functions lift groups pointwise.
-instance Group b => Group (a -> b) where
-  negateG f = negateG . f
-  (~~) = liftA2 (~~)
 instance Additive b => Additive (a -> b)