Add instances for Complex

src/lib/Witch/Instances.hs

@@ -5,6 +5,7 @@
 module Witch.Instances where
 
 import qualified Data.Bits as Bits
+import qualified Data.Complex as Complex
 import qualified Data.Fixed as Fixed
 import qualified Data.Int as Int
 import qualified Data.List.NonEmpty as NonEmpty
@@ -455,7 +456,9 @@ instance Integral a => Cast.Cast a (Ratio.Ratio a) where
   cast = (Ratio.% 1)
 
 instance Integral a => TryCast.TryCast (Ratio.Ratio a) a where
-  tryCast = maybeTryCast $ \ s -> if Ratio.denominator s == 1 then Just $ Ratio.numerator s else Nothing
+  tryCast = maybeTryCast $ \ s -> if Ratio.denominator s == 1
+    then Just $ Ratio.numerator s
+    else Nothing
 
 -- Fixed
 
@@ -465,6 +468,16 @@ instance Cast.Cast Integer (Fixed.Fixed a) where
 instance Cast.Cast (Fixed.Fixed a) Integer where
   cast (Fixed.MkFixed t) = t
 
+-- Complex
+
+instance Num a => Cast.Cast a (Complex.Complex a) where
+  cast = (Complex.:+ 0)
+
+instance (Eq a, Num a) => TryCast.TryCast (Complex.Complex a) a where
+  tryCast = maybeTryCast $ \ s -> if Complex.imagPart s == 0
+    then Just $ Complex.realPart s
+    else Nothing
+
 fromNonNegativeIntegral :: (Integral s, Num t) => s -> Maybe t
 fromNonNegativeIntegral x = if x < 0 then Nothing else Just $ fromIntegral x
 

src/test/Main.hs

@@ -4,6 +4,7 @@
 {-# LANGUAGE TemplateHaskell #-}
 {-# LANGUAGE TypeApplications #-}
 
+import Data.Complex
 import Data.Fixed
 import Data.Int
 import Data.List.NonEmpty
@@ -801,6 +802,19 @@ main = runTestTTAndExit $ "Witch" ~:
     , cast @Deci @Integer 1 ~?= 10
     ]
 
+  -- Complex
+
+  , "Cast a (Complex a)" ~:
+    [ cast @Float @(Complex Float) 1 ~?= 1
+    , cast @Double @(Complex Double) 1 ~?= 1
+    ]
+  , "TryCast (Complex a) a" ~:
+    [ tryCast @(Complex Float) @Float 1 ~?= Right 1
+    , tryCast @(Complex Float) @Float (0 :+ 1) ~?= Left (TryCastException $ 0 :+ 1)
+    , tryCast @(Complex Double) @Double 1 ~?= Right 1
+    , tryCast @(Complex Double) @Double (0 :+ 1) ~?= Left (TryCastException $ 0 :+ 1)
+    ]
+
   ]
 
 untested :: [Test]