Can I automatically implement classes?

Question

In Scalaz every Monad instance is automatically an instance of Applicative.

implicit val listInstance = new Monad[List] {
  def po         


        

Answer 1

It isn't currently possible, though it would be if you changed the existing library to support this. Turning DefaultSignatures on would let you write

class Applicative f where
    pure :: a -> f a
    (<*>) :: f (a -> b) -> f a -> f b

    default pure :: Monad f => a -> f a
    default (<*>) :: Monad f => f (a -> b) -> f a -> f b
    pure = return
    (<*>) = ap

Then once you had implemented instance Monad M where {- ... -}, a simple instance Applicative M (with no where or method definitions) would inherit these default implementations. I'm not sure why this wasn't done.