Document Rewrite

src/Rel8/Rewrite.hs

@@ -18,6 +18,10 @@ import Rel8.HigherKinded
 import Rel8.Top
 
 
+-- | @Rewrite f g a b@ says that @a@ can be rewritten into @b@ by changing the
+-- underlying data functor from @f@ to @g@. For higher-kinded data types, this
+-- is akin to a map operation @t f -> t g@, but this class specifically doesn't
+-- talk about higher-kinded data in order to be more general.
 class Rewrite f g a b | f g a -> b, a -> f, b -> g, f g b -> a where
   rewrite :: ( forall x. C f x -> C g x ) -> a -> b