Adding void instance (#47)

* Adding void instance

Resolves #46

* Remove SVoid

* Remove SigVoid

Author: ethul

src/Data/Generic.purs

@@ -85,6 +85,11 @@ instance genericUnit :: Generic Unit where
   fromSpine SUnit = Just unit
   fromSpine _ = Nothing
 
+instance genericVoid :: Generic Void where
+  toSpine = absurd
+  toSignature _ = SigProd "Data.Void.Void" []
+  fromSpine _ = Nothing
+
 instance genericTuple :: (Generic a, Generic b) => Generic (Tuple a b) where
   toSpine (Tuple x y) =
     SProd "Data.Tuple.Tuple" [\_ -> toSpine x, \_ -> toSpine y]

test/Main.purs

@@ -30,6 +30,10 @@ data UnitPlus = UnitPlus Unit Unit
 
 derive instance genericUnitPlus :: Generic UnitPlus
 
+data VoidPlus = VoidPlus Void Void
+
+derive instance genericVoidPlus :: Generic VoidPlus
+
 instance showFoo :: Show Foo where
   show = gShow