I try to write a list-corresponding reverse function under Monoid typeclass like this:
reverse :: [a] -> [a]
reverse ls = foldl ( \b a -> a:b ) [] ls
and my attempt is like this:
reverse :: (Foldable t, Applicative t, Monoid (t a)) => t a -> t a
reverse ls = foldl (\l r -> r `mappend` l ) mempty ls
But I received error message from console:
Occurs check: cannot construct the infinite type a ~ t a
I feel like I was missing something, any help will be appreciated.