Add roles declarations to forbid unsafe coercions (#120)

Author: kl0tl

src/CSS/Property.purs

@@ -40,6 +40,8 @@ quote s = "\"" <> s <> "\""
 newtype Key :: Type -> Type
 newtype Key a = Key Prefixed
 
+type role Key representational
+
 derive instance eqKey :: (Eq a) => Eq (Key a)
 derive instance ordKey :: (Ord a) => Ord (Key a)
 

src/CSS/Size.purs

@@ -9,6 +9,8 @@ import CSS.String (class IsString, fromString)
 newtype Size :: Type -> Type
 newtype Size a = Size Value
 
+type role Size nominal
+
 derive instance eqSize :: Eq a => Eq (Size a)
 derive instance ordSize :: Ord a => Ord (Size a)
 
@@ -81,6 +83,8 @@ data Rad
 newtype Angle :: Type -> Type
 newtype Angle a = Angle Value
 
+type role Angle nominal
+
 derive instance eqAngle :: Eq a => Eq (Angle a)
 derive instance ordAngle :: Ord a => Ord (Angle a)