Add instances for unsigned integral types

src/lib/Witch.hs

@@ -18,6 +18,7 @@ module Witch
   ) where
 
 import qualified Witch.Cast
+import Witch.Instances ()
 import qualified Witch.Lift
 import qualified Witch.Utility
 import qualified Witch.TryCast

src/lib/Witch/Cast.hs

@@ -4,56 +4,9 @@
 module Witch.Cast where
 
 import qualified Data.Coerce as Coerce
-import qualified Data.Int as Int
-import qualified Data.List.NonEmpty as NonEmpty
 
 class Cast source target where
   cast :: source -> target
 
   default cast :: Coerce.Coercible source target => source -> target
   cast = Coerce.coerce
-
-instance Cast (NonEmpty.NonEmpty a) [a] where
-  cast = NonEmpty.toList
-
-instance Cast Int.Int8 Int.Int16 where
-  cast = fromIntegral
-
-instance Cast Int.Int8 Int.Int32 where
-  cast = fromIntegral
-
-instance Cast Int.Int8 Int.Int64 where
-  cast = fromIntegral
-
-instance Cast Int.Int8 Int where
-  cast = fromIntegral
-
-instance Cast Int.Int8 Integer where
-  cast = fromIntegral
-
-instance Cast Int.Int16 Int.Int32 where
-  cast = fromIntegral
-
-instance Cast Int.Int16 Int.Int64 where
-  cast = fromIntegral
-
-instance Cast Int.Int16 Int where
-  cast = fromIntegral
-
-instance Cast Int.Int16 Integer where
-  cast = fromIntegral
-
-instance Cast Int.Int32 Int.Int64 where
-  cast = fromIntegral
-
-instance Cast Int.Int32 Integer where
-  cast = fromIntegral
-
-instance Cast Int.Int64 Integer where
-  cast = fromIntegral
-
-instance Cast Int Int.Int64 where
-  cast = fromIntegral
-
-instance Cast Int Integer where
-  cast = fromIntegral

src/lib/Witch/Instances.hs

@@ -0,0 +1,232 @@
+{-# OPTIONS_GHC -Wno-orphans #-}
+{-# LANGUAGE MultiParamTypeClasses #-}
+
+module Witch.Instances where
+
+import qualified Data.Bits as Bits
+import qualified Data.Int as Int
+import qualified Data.List.NonEmpty as NonEmpty
+import qualified Data.Word as Word
+import qualified Numeric.Natural as Natural
+import qualified Witch.Cast as Cast
+import qualified Witch.TryCast as TryCast
+import qualified Witch.TryCastException as TryCastException
+
+-- []
+
+instance TryCast.TryCast [a] (NonEmpty.NonEmpty a) where
+  tryCast = maybeTryCast NonEmpty.nonEmpty
+
+-- NonEmpty
+
+instance Cast.Cast (NonEmpty.NonEmpty a) [a] where
+  cast = NonEmpty.toList
+
+-- Int8
+
+instance Cast.Cast Int.Int8 Int.Int16 where
+  cast = fromIntegral
+
+instance Cast.Cast Int.Int8 Int.Int32 where
+  cast = fromIntegral
+
+instance Cast.Cast Int.Int8 Int.Int64 where
+  cast = fromIntegral
+
+instance Cast.Cast Int.Int8 Int where
+  cast = fromIntegral
+
+instance Cast.Cast Int.Int8 Integer where
+  cast = fromIntegral
+
+-- Int16
+
+instance TryCast.TryCast Int.Int16 Int.Int8 where
+  tryCast = maybeTryCast Bits.toIntegralSized
+
+instance Cast.Cast Int.Int16 Int.Int32 where
+  cast = fromIntegral
+
+instance Cast.Cast Int.Int16 Int.Int64 where
+  cast = fromIntegral
+
+instance Cast.Cast Int.Int16 Int where
+  cast = fromIntegral
+
+instance Cast.Cast Int.Int16 Integer where
+  cast = fromIntegral
+
+-- Int32
+
+instance TryCast.TryCast Int.Int32 Int.Int8 where
+  tryCast = maybeTryCast Bits.toIntegralSized
+
+instance TryCast.TryCast Int.Int32 Int.Int16 where
+  tryCast = maybeTryCast Bits.toIntegralSized
+
+instance Cast.Cast Int.Int32 Int.Int64 where
+  cast = fromIntegral
+
+instance TryCast.TryCast Int.Int32 Int where
+  tryCast = maybeTryCast Bits.toIntegralSized
+
+instance Cast.Cast Int.Int32 Integer where
+  cast = fromIntegral
+
+-- Int64
+
+instance TryCast.TryCast Int.Int64 Int.Int8 where
+  tryCast = maybeTryCast Bits.toIntegralSized
+
+instance TryCast.TryCast Int.Int64 Int.Int16 where
+  tryCast = maybeTryCast Bits.toIntegralSized
+
+instance TryCast.TryCast Int.Int64 Int.Int32 where
+  tryCast = maybeTryCast Bits.toIntegralSized
+
+instance TryCast.TryCast Int.Int64 Int where
+  tryCast = maybeTryCast Bits.toIntegralSized
+
+instance Cast.Cast Int.Int64 Integer where
+  cast = fromIntegral
+
+-- Int
+
+instance TryCast.TryCast Int Int.Int8 where
+  tryCast = maybeTryCast Bits.toIntegralSized
+
+instance TryCast.TryCast Int Int.Int16 where
+  tryCast = maybeTryCast Bits.toIntegralSized
+
+instance TryCast.TryCast Int Int.Int32 where
+  tryCast = maybeTryCast Bits.toIntegralSized
+
+instance Cast.Cast Int Int.Int64 where
+  cast = fromIntegral
+
+instance Cast.Cast Int Integer where
+  cast = fromIntegral
+
+-- Integer
+
+instance TryCast.TryCast Integer Int.Int8 where
+  tryCast = maybeTryCast Bits.toIntegralSized
+
+instance TryCast.TryCast Integer Int.Int16 where
+  tryCast = maybeTryCast Bits.toIntegralSized
+
+instance TryCast.TryCast Integer Int.Int32 where
+  tryCast = maybeTryCast Bits.toIntegralSized
+
+instance TryCast.TryCast Integer Int.Int64 where
+  tryCast = maybeTryCast Bits.toIntegralSized
+
+instance TryCast.TryCast Integer Int where
+  tryCast = maybeTryCast Bits.toIntegralSized
+
+-- Word8
+
+instance Cast.Cast Word.Word8 Word.Word16 where
+  cast = fromIntegral
+
+instance Cast.Cast Word.Word8 Word.Word32 where
+  cast = fromIntegral
+
+instance Cast.Cast Word.Word8 Word.Word64 where
+  cast = fromIntegral
+
+instance Cast.Cast Word.Word8 Word where
+  cast = fromIntegral
+
+instance Cast.Cast Word.Word8 Natural.Natural where
+  cast = fromIntegral
+
+-- Word16
+
+instance TryCast.TryCast Word.Word16 Word.Word8 where
+  tryCast = maybeTryCast Bits.toIntegralSized
+
+instance Cast.Cast Word.Word16 Word.Word32 where
+  cast = fromIntegral
+
+instance Cast.Cast Word.Word16 Word.Word64 where
+  cast = fromIntegral
+
+instance Cast.Cast Word.Word16 Word where
+  cast = fromIntegral
+
+instance Cast.Cast Word.Word16 Natural.Natural where
+  cast = fromIntegral
+
+-- Word32
+
+instance TryCast.TryCast Word.Word32 Word.Word8 where
+  tryCast = maybeTryCast Bits.toIntegralSized
+
+instance TryCast.TryCast Word.Word32 Word.Word16 where
+  tryCast = maybeTryCast Bits.toIntegralSized
+
+instance Cast.Cast Word.Word32 Word.Word64 where
+  cast = fromIntegral
+
+instance TryCast.TryCast Word.Word32 Word where
+  tryCast = maybeTryCast Bits.toIntegralSized
+
+instance Cast.Cast Word.Word32 Natural.Natural where
+  cast = fromIntegral
+
+-- Word64
+
+instance TryCast.TryCast Word.Word64 Word.Word8 where
+  tryCast = maybeTryCast Bits.toIntegralSized
+
+instance TryCast.TryCast Word.Word64 Word.Word16 where
+  tryCast = maybeTryCast Bits.toIntegralSized
+
+instance TryCast.TryCast Word.Word64 Word.Word32 where
+  tryCast = maybeTryCast Bits.toIntegralSized
+
+instance TryCast.TryCast Word.Word64 Word where
+  tryCast = maybeTryCast Bits.toIntegralSized
+
+instance Cast.Cast Word.Word64 Natural.Natural where
+  cast = fromIntegral
+
+-- Word
+
+instance TryCast.TryCast Word Word.Word8 where
+  tryCast = maybeTryCast Bits.toIntegralSized
+
+instance TryCast.TryCast Word Word.Word16 where
+  tryCast = maybeTryCast Bits.toIntegralSized
+
+instance TryCast.TryCast Word Word.Word32 where
+  tryCast = maybeTryCast Bits.toIntegralSized
+
+instance Cast.Cast Word Word.Word64 where
+  cast = fromIntegral
+
+instance Cast.Cast Word Natural.Natural where
+  cast = fromIntegral
+
+-- Natural
+
+instance TryCast.TryCast Natural.Natural Word.Word8 where
+  tryCast = maybeTryCast Bits.toIntegralSized
+
+instance TryCast.TryCast Natural.Natural Word.Word16 where
+  tryCast = maybeTryCast Bits.toIntegralSized
+
+instance TryCast.TryCast Natural.Natural Word.Word32 where
+  tryCast = maybeTryCast Bits.toIntegralSized
+
+instance TryCast.TryCast Natural.Natural Word.Word64 where
+  tryCast = maybeTryCast Bits.toIntegralSized
+
+instance TryCast.TryCast Natural.Natural Word where
+  tryCast = maybeTryCast Bits.toIntegralSized
+
+maybeTryCast :: (s -> Maybe t) -> s -> Either (TryCastException.TryCastException s t) t
+maybeTryCast f s = case f s of
+  Nothing -> Left $ TryCastException.TryCastException s
+  Just t -> Right t

src/lib/Witch/TryCast.hs

@@ -2,63 +2,7 @@
 
 module Witch.TryCast where
 
-import qualified Data.List.NonEmpty as NonEmpty
-import qualified Data.Bits as Bits
-import qualified Data.Int as Int
 import qualified Witch.TryCastException as TryCastException
 
 class TryCast source target where
   tryCast :: source -> Either (TryCastException.TryCastException source target) target
-
-instance TryCast [a] (NonEmpty.NonEmpty a) where
-  tryCast = maybeTryCast NonEmpty.nonEmpty
-
-instance TryCast Int.Int16 Int.Int8 where
-  tryCast = maybeTryCast Bits.toIntegralSized
-
-instance TryCast Int.Int32 Int.Int8 where
-  tryCast = maybeTryCast Bits.toIntegralSized
-
-instance TryCast Int.Int32 Int.Int16 where
-  tryCast = maybeTryCast Bits.toIntegralSized
-
-instance TryCast Int.Int32 Int where
-  tryCast = maybeTryCast Bits.toIntegralSized
-
-instance TryCast Int.Int64 Int.Int8 where
-  tryCast = maybeTryCast Bits.toIntegralSized
-
-instance TryCast Int.Int64 Int.Int16 where
-  tryCast = maybeTryCast Bits.toIntegralSized
-
-instance TryCast Int.Int64 Int.Int32 where
-  tryCast = maybeTryCast Bits.toIntegralSized
-
-instance TryCast Int.Int64 Int where
-  tryCast = maybeTryCast Bits.toIntegralSized
-
-instance TryCast Int Int.Int8 where
-  tryCast = maybeTryCast Bits.toIntegralSized
-
-instance TryCast Int Int.Int16 where
-  tryCast = maybeTryCast Bits.toIntegralSized
-
-instance TryCast Int Int.Int32 where
-  tryCast = maybeTryCast Bits.toIntegralSized
-
-instance TryCast Integer Int.Int8 where
-  tryCast = maybeTryCast Bits.toIntegralSized
-
-instance TryCast Integer Int.Int16 where
-  tryCast = maybeTryCast Bits.toIntegralSized
-
-instance TryCast Integer Int.Int32 where
-  tryCast = maybeTryCast Bits.toIntegralSized
-
-instance TryCast Integer Int.Int64 where
-  tryCast = maybeTryCast Bits.toIntegralSized
-
-maybeTryCast :: (s -> Maybe t) -> s -> Either (TryCastException.TryCastException s t) t
-maybeTryCast f s = case f s of
-  Nothing -> Left $ TryCastException.TryCastException s
-  Just t -> Right t

src/test/Main.hs

@@ -1,21 +1,58 @@
+{-# OPTIONS_GHC -Wno-missing-import-lists #-}
+{-# LANGUAGE CPP #-}
+{-# LANGUAGE FlexibleInstances #-}
+{-# LANGUAGE MultiParamTypeClasses #-}
+{-# LANGUAGE TemplateHaskell #-}
 {-# LANGUAGE TypeApplications #-}
 
 import Data.Int
 import Data.List.NonEmpty
+import Data.Word
+import Numeric.Natural
 import Test.HUnit
 import Witch
 
 main :: IO ()
 main = runTestTTAndExit $ "Witch" ~:
-  [ "Cast (NonEmpty a) [a]" ~:
-    [ cast ('a' :| []) ~?= "a"
-    , cast ('a' :| "b") ~?= "ab"
-    ]
+  [ as @Int8 1 ~?= 1
+  , cast (1 :: Int8) ~?= (1 :: Int16)
+  , from @Int8 1 ~?= (1 :: Int)
+  , into @Int16 (1 :: Int8) ~?= 1
+  , over @String (<> "!") (Name "Simon") ~?= Name "Simon!"
+  , via @Int16 (1 :: Int8) ~?= (1 :: Int32)
+  , tryFrom @Int16 1 ~?= Right (1 :: Int8)
+  , tryInto @Int8 (1 :: Int16) ~?= Right 1
+  , unsafeCast (1 :: Int16) ~?= (1 :: Int8)
+  , unsafeFrom @Int16 1 ~?= (1 :: Int8)
+  , unsafeInto @Int8 (1 :: Int16) ~?= 1
+
+# if MIN_VERSION_GLASGOW_HASKELL(8, 10, 1, 0)
+  , ($$(liftedCast (1 :: Int16)) :: Int8) ~?= 1
+  , ($$(liftedFrom @Int16 1) :: Int8) ~?= 1
+  , ($$(liftedInto @Int8 (1 :: Int16)) :: Int8) ~?= 1
+# else
+  , ($(liftedCast (1 :: Int16)) :: Int8) ~?= 1
+  , ($(liftedFrom @Int16 1) :: Int8) ~?= 1
+  , ($(liftedInto @Int8 (1 :: Int16)) :: Int8) ~?= 1
+# endif
+
+  -- []
+
   , "TryCast [a] (NonEmpty a)" ~:
-    [ tryInto @(NonEmpty Char) "" ~?= Left (TryCastException "")
-    , tryCast "a" ~?= Right ('a' :| [])
-    , tryCast "ab" ~?= Right ('a' :| "b")
+    [ tryCast @[Int] @(NonEmpty Int) [] ~?= Left (TryCastException [])
+    , tryCast @[Int] @(NonEmpty Int) [1] ~?= Right (1 :| [])
+    , tryCast @[Int] @(NonEmpty Int) [1, 2] ~?= Right (1 :| [2])
     ]
+
+  -- NonEmpty
+
+  , "Cast (NonEmpty a) [a]" ~:
+    [ cast @(NonEmpty Int) @[Int] (1 :| []) ~?= [1]
+    , cast @(NonEmpty Int) @[Int] (1 :| [2]) ~?= [1, 2]
+    ]
+
+  -- Int8
+
   , "Cast Int8 Int16" ~:
     [ cast @Int8 @Int16 0 ~?= 0
     , cast @Int8 @Int16 127 ~?= 127
@@ -41,6 +78,9 @@ main = runTestTTAndExit $ "Witch" ~:
     , cast @Int8 @Integer 127 ~?= 127
     , cast @Int8 @Integer (-128) ~?= -128
     ]
+
+  -- Int16
+
   , "TryCast Int16 Int8" ~:
     [ tryCast @Int16 @Int8 0 ~?= Right 0
     , tryCast @Int16 @Int8 127 ~?= Right 127
@@ -68,6 +108,9 @@ main = runTestTTAndExit $ "Witch" ~:
     , cast @Int16 @Integer 32767 ~?= 32767
     , cast @Int16 @Integer (-32768) ~?= -32768
     ]
+
+  -- Int32
+
   , "TryCast Int32 Int8" ~:
     [ tryCast @Int32 @Int8 0 ~?= Right 0
     , tryCast @Int32 @Int8 127 ~?= Right 127
@@ -99,6 +142,9 @@ main = runTestTTAndExit $ "Witch" ~:
     , cast @Int32 @Integer 2147483647 ~?= 2147483647
     , cast @Int32 @Integer (-2147483648) ~?= -2147483648
     ]
+
+  -- Int64
+
   , "TryCast Int64 Int8" ~:
     [ tryCast @Int64 @Int8 0 ~?= Right 0
     , tryCast @Int64 @Int8 127 ~?= Right 127
@@ -132,6 +178,9 @@ main = runTestTTAndExit $ "Witch" ~:
     , cast @Int64 @Integer 9223372036854775807 ~?= 9223372036854775807
     , cast @Int64 @Integer (-9223372036854775808) ~?= -9223372036854775808
     ]
+
+  -- Int
+
   , "TryCast Int Int8" ~:
     [ tryCast @Int @Int8 0 ~?= Right 0
     , tryCast @Int @Int8 127 ~?= Right 127
@@ -165,6 +214,9 @@ main = runTestTTAndExit $ "Witch" ~:
     , cast @Int @Integer maxBound ~?= fromIntegral (maxBound :: Int)
     , cast @Int @Integer minBound ~?= fromIntegral (minBound :: Int)
     ]
+
+  -- Integer
+
   , "TryCast Integer Int8" ~:
     [ tryCast @Integer @Int8 0 ~?= Right 0
     , tryCast @Integer @Int8 127 ~?= Right 127
@@ -193,4 +245,184 @@ main = runTestTTAndExit $ "Witch" ~:
     , tryCast @Integer @Int64 (-9223372036854775808) ~?= Right (-9223372036854775808)
     , tryCast @Integer @Int64 (-9223372036854775809) ~?= Left (TryCastException $ -9223372036854775809)
     ]
+  , "TryCast Integer Int" ~:
+    [ tryCast @Integer @Int 0 ~?= Right 0
+    , let x = maxBound :: Int
+      in tryCast @Integer @Int (fromIntegral x) ~?= Right x
+    , let x = toInteger (maxBound :: Int) + 1
+      in tryCast @Integer @Int x ~?= Left (TryCastException x)
+    , let x = minBound :: Int
+      in tryCast @Integer @Int (fromIntegral x) ~?= Right x
+    , let x = toInteger (minBound :: Int) - 1
+      in tryCast @Integer @Int x ~?= Left (TryCastException x)
+    ]
+
+  -- Word8
+
+  , "Cast Word8 Word16" ~:
+    [ cast @Word8 @Word16 0 ~?= 0
+    , cast @Word8 @Word16 255 ~?= 255
+    ]
+  , "Cast Word8 Word32" ~:
+    [ cast @Word8 @Word32 0 ~?= 0
+    , cast @Word8 @Word32 255 ~?= 255
+    ]
+  , "Cast Word8 Word64" ~:
+    [ cast @Word8 @Word64 0 ~?= 0
+    , cast @Word8 @Word64 255 ~?= 255
+    ]
+  , "Cast Word8 Word" ~:
+    [ cast @Word8 @Word 0 ~?= 0
+    , cast @Word8 @Word 255 ~?= 255
+    ]
+  , "Cast Word8 Natural" ~:
+    [ cast @Word8 @Natural 0 ~?= 0
+    , cast @Word8 @Natural 255 ~?= 255
+    ]
+
+  -- Word16
+
+  , "TryCast Word16 Word8" ~:
+    [ tryCast @Word16 @Word8 0 ~?= Right 0
+    , tryCast @Word16 @Word8 255 ~?= Right 255
+    , tryCast @Word16 @Word8 256 ~?= Left (TryCastException 256)
+    ]
+  , "Cast Word16 Word32" ~:
+    [ cast @Word16 @Word32 0 ~?= 0
+    , cast @Word16 @Word32 65535 ~?= 65535
+    ]
+  , "Cast Word16 Word64" ~:
+    [ cast @Word16 @Word64 0 ~?= 0
+    , cast @Word16 @Word64 65535 ~?= 65535
+    ]
+  , "Cast Word16 Word" ~:
+    [ cast @Word16 @Word 0 ~?= 0
+    , cast @Word16 @Word 65535 ~?= 65535
+    ]
+  , "Cast Word16 Natural" ~:
+    [ cast @Word16 @Natural 0 ~?= 0
+    , cast @Word16 @Natural 65535 ~?= 65535
+    ]
+
+  -- Word32
+
+  , "TryCast Word32 Word8" ~:
+    [ tryCast @Word32 @Word8 0 ~?= Right 0
+    , tryCast @Word32 @Word8 255 ~?= Right 255
+    , tryCast @Word32 @Word8 256 ~?= Left (TryCastException 256)
+    ]
+  , "TryCast Word32 Word16" ~:
+    [ tryCast @Word32 @Word16 0 ~?= Right 0
+    , tryCast @Word32 @Word16 65535 ~?= Right 65535
+    , tryCast @Word32 @Word16 65536 ~?= Left (TryCastException 65536)
+    ]
+  , "Cast Word32 Word64" ~:
+    [ cast @Word32 @Word64 0 ~?= 0
+    , cast @Word32 @Word64 4294967295 ~?= 4294967295
+    ]
+  , "TryCast Word32 Word" ~:
+    if toInteger (maxBound :: Word) >= 4294967295 then
+      [ tryCast @Word32 @Word 0 ~?= Right 0
+      , tryCast @Word32 @Word 4294967295 ~?= Right 4294967295
+      ]
+    else [False ~? "untested"]
+  , "Cast Word32 Natural" ~:
+    [ cast @Word32 @Natural 0 ~?= 0
+    , cast @Word32 @Natural 4294967295 ~?= 4294967295
+    ]
+
+  -- Word64
+
+  , "TryCast Word64 Word8" ~:
+    [ tryCast @Word64 @Word8 0 ~?= Right 0
+    , tryCast @Word64 @Word8 255 ~?= Right 255
+    , tryCast @Word64 @Word8 256 ~?= Left (TryCastException 256)
+    ]
+  , "TryCast Word64 Word16" ~:
+    [ tryCast @Word64 @Word16 0 ~?= Right 0
+    , tryCast @Word64 @Word16 65535 ~?= Right 65535
+    , tryCast @Word64 @Word16 65536 ~?= Left (TryCastException 65536)
+    ]
+  , "TryCast Word64 Word32" ~:
+    [ tryCast @Word64 @Word32 0 ~?= Right 0
+    , tryCast @Word64 @Word32 4294967295 ~?= Right 4294967295
+    , tryCast @Word64 @Word32 4294967296 ~?= Left (TryCastException 4294967296)
+    ]
+  , "TryCast Word64 Word" ~:
+    if toInteger (maxBound :: Word) >= 18446744073709551615 then
+      [ tryCast @Word64 @Word 0 ~?= Right 0
+      , tryCast @Word64 @Word 18446744073709551615 ~?= Right 18446744073709551615
+      ]
+    else [False ~? "untested"]
+  , "Cast Word64 Natural" ~:
+    [ cast @Word64 @Natural 0 ~?= 0
+    , cast @Word64 @Natural 18446744073709551615 ~?= 18446744073709551615
+    ]
+
+  -- Word
+
+  , "TryCast Word Word8" ~:
+    [ tryCast @Word @Word8 0 ~?= Right 0
+    , tryCast @Word @Word8 255 ~?= Right 255
+    , tryCast @Word @Word8 256 ~?= Left (TryCastException 256)
+    ]
+  , "TryCast Word Word16" ~:
+    [ tryCast @Word @Word16 0 ~?= Right 0
+    , tryCast @Word @Word16 65535 ~?= Right 65535
+    , tryCast @Word @Word16 65536 ~?= Left (TryCastException 65536)
+    ]
+  , "TryCast Word Word32" ~:
+    if toInteger (maxBound :: Word) >= 4294967295 then
+      [ tryCast @Word @Word32 0 ~?= Right 0
+      , tryCast @Word @Word32 4294967295 ~?= Right 4294967295
+      , tryCast @Word @Word32 4294967296 ~?= Left (TryCastException 4294967296)
+      ]
+    else [False ~? "untested"]
+  , "Cast Word Word64" ~:
+    [ cast @Word @Word64 0 ~?= 0
+    , cast @Word @Word64 maxBound ~?= fromIntegral (maxBound :: Word)
+    ]
+  , "Cast Word Natural" ~:
+    [ cast @Word @Natural 0 ~?= 0
+    , cast @Word @Natural maxBound ~?= fromIntegral (maxBound :: Word)
+    ]
+
+  -- Natural
+
+  , "TryCast Natural Word8" ~:
+    [ tryCast @Natural @Word8 0 ~?= Right 0
+    , tryCast @Natural @Word8 255 ~?= Right 255
+    , tryCast @Natural @Word8 256 ~?= Left (TryCastException 256)
+    ]
+  , "TryCast Natural Word16" ~:
+    [ tryCast @Natural @Word16 0 ~?= Right 0
+    , tryCast @Natural @Word16 65535 ~?= Right 65535
+    , tryCast @Natural @Word16 65536 ~?= Left (TryCastException 65536)
+    ]
+  , "TryCast Natural Word32" ~:
+    [ tryCast @Natural @Word32 0 ~?= Right 0
+    , tryCast @Natural @Word32 4294967295 ~?= Right 4294967295
+    , tryCast @Natural @Word32 4294967296 ~?= Left (TryCastException 4294967296)
+    ]
+  , "TryCast Natural Word64" ~:
+    [ tryCast @Natural @Word64 0 ~?= Right 0
+    , tryCast @Natural @Word64 18446744073709551615 ~?= Right 18446744073709551615
+    , tryCast @Natural @Word64 18446744073709551616 ~?= Left (TryCastException 18446744073709551616)
+    ]
+  , "TryCast Natural Word" ~:
+    [ tryCast @Natural @Word 0 ~?= Right 0
+    , let x = maxBound :: Word
+      in tryCast @Natural @Word (fromIntegral x) ~?= Right x
+    , let x = fromIntegral (maxBound :: Word) + 1 :: Natural
+      in tryCast @Natural @Word x ~?= Left (TryCastException x)
+    ]
+
   ]
+
+newtype Name
+  = Name String
+  deriving (Eq, Show)
+
+instance Cast Name String
+
+instance Cast String Name

stack.yaml

@@ -1 +1 @@
-resolver: lts-17.0
+resolver: nightly-2021-04-06

witch.cabal

@@ -25,6 +25,7 @@ library
     Witch
     Witch.Cast
     Witch.Identity
+    Witch.Instances
     Witch.Lift
     Witch.TryCast
     Witch.TryCastException