From 1d660f8a8c44c99ce3b714211006b6e2a858ada5 Mon Sep 17 00:00:00 2001
From: Taylor Fausak <taylor@fausak.me>
Date: Mon, 10 May 2021 18:51:40 -0400
Subject: [PATCH] Remove casting type wrapper

---
 src/lib/Witch.hs         |  4 ---
 src/lib/Witch/Casting.hs | 62 ----------------------------------------
 src/test/Main.hs         | 42 +--------------------------
 witch.cabal              |  1 -
 4 files changed, 1 insertion(+), 108 deletions(-)
 delete mode 100644 src/lib/Witch/Casting.hs

diff --git a/src/lib/Witch.hs b/src/lib/Witch.hs
index 528cff2..94a1d3e 100644
--- a/src/lib/Witch.hs
+++ b/src/lib/Witch.hs
@@ -55,9 +55,6 @@ module Witch
   -- * Data types
   , Witch.TryCastException.TryCastException(..)
 
-  -- ** Casting
-  , Witch.Casting.Casting(Casting)
-
   -- * Notes
 
   -- ** Motivation
@@ -193,7 +190,6 @@ module Witch
   ) where
 
 import qualified Witch.Cast
-import qualified Witch.Casting
 import Witch.Instances ()
 import qualified Witch.Lift
 import qualified Witch.TryCast
diff --git a/src/lib/Witch/Casting.hs b/src/lib/Witch/Casting.hs
deleted file mode 100644
index a3e0138..0000000
--- a/src/lib/Witch/Casting.hs
+++ /dev/null
@@ -1,62 +0,0 @@
-{-# LANGUAGE FlexibleInstances #-}
-{-# LANGUAGE MultiParamTypeClasses #-}
-{-# LANGUAGE ScopedTypeVariables #-}
-{-# LANGUAGE TypeApplications #-}
-
-module Witch.Casting where
-
-import qualified Data.Bifunctor as Bifunctor
-import qualified Data.Function as Function
-import qualified Witch.Cast as Cast
-
--- | This type mostly exists to make it easier to derive instances through
--- some other type. It does this by leaning on the 'Cast.Cast' type class. For
--- example, consider this data type:
---
--- > data Toggle = Off | On
--- > instance Cast Toggle String where
--- >   cast toggle = case toggle of
--- >     Off -> "off"
--- >     On -> "on"
---
--- If you wanted to implement a 'Show' instance for @Toggle@ by going through
--- a 'String', you would need to write something like this:
---
--- > instance Show Toggle where
--- >   show = show . into @String
---
--- That may not very complicated, but at the same time it is not very
--- interesting. And it can be tricky if you want to keep other instances (like
--- 'Read') in sync. That's where the 'Casting' type comes in! You can
--- derive the above instance like so:
---
--- > data Toggle = Off | On
--- >   deriving Show via Casting Toggle String
-newtype Casting source target
-  = Casting source
-
--- | Uses @coerce@.
-instance Cast.Cast s (Casting s t)
-
--- | Uses @coerce@.
-instance Cast.Cast (Casting s t) s
-
-instance (Cast.Cast t s, Bounded t) => Bounded (Casting s t) where
-  maxBound = Cast.cast $ Cast.cast @t @s maxBound
-  minBound = Cast.cast $ Cast.cast @t @s minBound
-
-instance (Cast.Cast s t, Cast.Cast t s, Enum t) => Enum (Casting s t) where
-  fromEnum = fromEnum . Cast.cast @s @t . Cast.cast
-  toEnum = Cast.cast . Cast.cast @t @s . toEnum
-
-instance (Cast.Cast s t, Eq t) => Eq (Casting s t) where
-  (==) = Function.on (==) $ Cast.cast @s @t . Cast.cast
-
-instance (Cast.Cast s t, Ord t) => Ord (Casting s t) where
-  compare = Function.on compare $ Cast.cast @s @t . Cast.cast
-
-instance (Cast.Cast t s, Read t) => Read (Casting s t) where
-  readsPrec = fmap (fmap . Bifunctor.first $ Cast.cast . Cast.cast @t @s) . readsPrec
-
-instance (Cast.Cast s t, Show t) => Show (Casting s t) where
-  show = show . Cast.cast @s @t . Cast.cast
diff --git a/src/test/Main.hs b/src/test/Main.hs
index cdc0b4a..fafb84e 100644
--- a/src/test/Main.hs
+++ b/src/test/Main.hs
@@ -1659,46 +1659,6 @@ main = Hspec.hspec . Hspec.describe "Witch" $ do
       let f = Witch.cast @(Witch.TryCastException Bool Int) @LazyText.Text
       test $ f (Witch.TryCastException False Nothing) `Hspec.shouldBe` LazyText.pack "TryCastException @Bool @Int False Nothing"
 
-  -- Casting
-
-  Hspec.describe "Casting" $ do
-
-    Hspec.describe "Bounded" $ do
-
-      Hspec.it "maxBound" $ do
-        maxBound `Hspec.shouldBe` Age maxBound
-
-      Hspec.it "minBound" $ do
-        minBound `Hspec.shouldBe` Age minBound
-
-    Hspec.describe "Enum" $ do
-
-      Hspec.prop "fromEnum" $ \x ->
-        fromEnum (Age x) === fromEnum x
-
-      Hspec.prop "toEnum" $ \x ->
-        toEnum x === Age (toEnum x)
-
-    Hspec.describe "Eq" $ do
-
-      Hspec.prop "==" $ \x ->
-        Age x === Age x
-
-    Hspec.describe "Ord" $ do
-
-      Hspec.prop "compare" $ \x y ->
-        compare (Age x) (Age y) === compare x y
-
-    Hspec.describe "Read" $ do
-
-      Hspec.prop "readMaybe" $ \x ->
-        Read.readMaybe x === fmap Age (Read.readMaybe x)
-
-    Hspec.describe "Show" $ do
-
-      Hspec.prop "show" $ \x ->
-        show (Age x) === show x
-
 test :: Hspec.Example a => a -> Hspec.SpecWith (Hspec.Arg a)
 test = Hspec.it ""
 
@@ -1716,7 +1676,7 @@ instance Exception.Exception Untested
 
 newtype Age
   = Age Int.Int8
-  deriving (Bounded, Enum, Eq, Ord, Read, Show) via Witch.Casting Age Int.Int8
+  deriving (Eq, Show)
 
 instance Witch.Cast Age Int.Int8
 
diff --git a/witch.cabal b/witch.cabal
index d9114f4..fb7ff6b 100644
--- a/witch.cabal
+++ b/witch.cabal
@@ -47,7 +47,6 @@ library
   exposed-modules:
     Witch
     Witch.Cast
-    Witch.Casting
     Witch.Identity
     Witch.Instances
     Witch.Lift