Use generic-deriving for Show instance

It's quite possible that more of the classes can be removed in favour of
generic-deriving, but this fixes #12 regardless.

README.md

@@ -120,10 +120,7 @@ Other 'Alternative'-style functors lead to very different results:
 ```haskell
 eg1 :: Labels Triple
 eg1 = mempty
--- Triple
---   Const ""
---   Const ""
---   Const ""
+-- Triple (Const {getConst = ""}) (Const {getConst = ""}) (Const { getConst = ""})
 ```
 
 Of course, this method requires every field to be monoidal. If we try with
@@ -156,10 +153,7 @@ behaviours:
 ```haskell
 eg4 :: Partial Triple
 eg4 = deconstruct @Last triple
--- Triple
---   Last {getLast = Just 123}
---   Last {getLast = Just ()}
---   Last {getLast = Just "ABC"}
+-- Triple (Last {getLast = Just 123}) (Last {getLast = Just ()}) (Last {getLast = Just "ABC"})
 ```
 
 There's also `construct` for when we want to escape our `HKD` wrapper, and
@@ -214,8 +208,8 @@ eg10 :: Partial User
 eg10 = eg0 & field @"name"      .~ pure "Evil Tom"
            & field @"likesDogs" .~ pure False
 -- User
---   { name      = Last {getLast = Just "Evil Tom"}
---   , age       = Last {getLast = Nothing}
+--   { name = Last {getLast = Just "Evil Tom"}
+--   , age = Last {getLast = Nothing}
 --   , likesDogs = Last {getLast = Just False}
 --   }
 ```
@@ -249,10 +243,7 @@ product types:
 eg13 :: Labels Triple
 eg13 = mempty & position @1 .~ Const "hello"
               & position @2 .~ Const "world"
--- Triple
---   Const "hello"
---   Const "world"
---   Const ""
+-- Triple (Const {getConst = "hello"}) (Const {getConst = "world"}) (Const {getConst = ""})
 ```
 
 Again, this is a `Lens`, so we can just as easily _set_ values:
@@ -261,8 +252,8 @@ Again, this is a `Lens`, so we can just as easily _set_ values:
 eg14 :: Partial User
 eg14 = eg10 & position @2 .~ pure 25
 -- User
---   { name      = Last {getLast = Just "Evil Tom"}
---   , age       = Last {getLast = Just 25}
+--   { name = Last {getLast = Just "Evil Tom"}
+--   , age = Last {getLast = Just 25}
 --   , likesDogs = Last {getLast = Just False}
 --   }
 ```

higgledy.cabal

@@ -25,6 +25,7 @@ library
   -- other-extensions:
   build-depends:       base ^>= 4.12
                      , barbies ^>= 1.1.0
+                     , generic-deriving ^>= 1.12
                      , generic-lens ^>= 1.1.0
                      , QuickCheck >= 2.12.6 && < 2.14
   hs-source-dirs:      src

src/Data/Generic/HKD/Construction.hs

@@ -47,7 +47,7 @@ import GHC.Generics
 -- We can also /deconstruct/ a tuple into a partial structure:
 --
 -- >>> deconstruct @[] ("Hello", True)
--- (,) ["Hello"] [True]
+-- (,) (["Hello"],[True])
 --
 -- These two methods also satisfy the round-tripping property:
 --

src/Data/Generic/HKD/Labels.hs

@@ -32,7 +32,7 @@ import GHC.TypeLits (ErrorMessage (..), KnownSymbol, TypeError, symbolVal)
 --
 -- >>> data User = User { name :: String, age :: Int } deriving Generic
 -- >>> label @User
--- User {name = Const "name", age = Const "age"}
+-- User {name = Const {getConst = "name"}, age = Const {getConst = "age"}}
 class Label (structure :: Type) where
   label :: HKD structure (Const String)
 

src/Data/Generic/HKD/Types.hs

@@ -41,6 +41,7 @@ import Data.Proxy (Proxy (..))
 import Data.Void (Void)
 import GHC.Generics
 import GHC.TypeLits (KnownSymbol, symbolVal)
+import Generics.Deriving.Show (GShow' (..), gshowsPrecdefault)
 import Test.QuickCheck.Arbitrary (Arbitrary (..), CoArbitrary (..))
 import Test.QuickCheck.Function (Function (..), functionMap)
 
@@ -79,7 +80,7 @@ import Test.QuickCheck.Function (Function (..), functionMap)
 -- User {name = Last {getLast = Nothing}, age = Last {getLast = Nothing}}
 --
 -- >>> mempty @(HKD (Int, Bool) [])
--- (,) [] []
+-- (,) ([],[])
 newtype HKD (structure :: Type) (f :: Type -> Type)
   = HKD { runHKD :: HKD_ f structure Void }
 
@@ -138,41 +139,9 @@ instance (Generic structure, Function tuple, Tuple f structure tuple)
 
 -------------------------------------------------------------------------------
 
-class GShow (named :: Bool) (rep :: Type -> Type) where
-  gshow :: rep p -> String
-
-instance GShow named inner => GShow named (D1 meta inner) where
-  gshow = gshow @named . unM1
-
-instance (GShow 'True inner, KnownSymbol name)
-    => GShow any (C1 ('MetaCons name fixity 'True) inner) where
-  gshow (M1 x) = symbolVal (Proxy @name) <> " {" <> gshow @'True x <> "}"
-
-instance (GShow 'False inner, KnownSymbol name)
-    => GShow any (C1 ('MetaCons name fixity 'False) inner) where
-  gshow (M1 x) = symbolVal (Proxy @name) <> " " <> gshow @'False x
-
-instance (GShow 'True left, GShow 'True right)
-    => GShow 'True (left :*: right) where
-  gshow (left :*: right) = gshow @'True left <> ", " <> gshow @'True right
-
-instance (GShow 'False left, GShow 'False right)
-    => GShow 'False (left :*: right) where
-  gshow (left :*: right) = gshow @'False left <> " " <> gshow @'False right
-
-instance (GShow 'True inner, KnownSymbol field)
-    => GShow 'True (S1 ('MetaSel ('Just field) i d c) inner) where
-  gshow (M1 inner) = symbolVal (Proxy @field) <> " = " <> gshow @'True inner
-
-instance GShow 'False inner => GShow 'False (S1 meta inner) where
-  gshow (M1 inner) = gshow @'False inner
-
-instance (Show (f inner)) => GShow named (K1 R (f inner)) where
-  gshow (K1 x) = show x
-
-instance (Generic structure, GShow 'True (HKD_ f structure))
+instance (Generic (HKD structure f), GShow' (GHKD_ f (Rep structure)))
     => Show (HKD structure f) where
-  show (HKD x) = gshow @'True x
+  showsPrec = gshowsPrecdefault
 
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