Re: [Haskell-beginners] applicative instance

Yep that worked, thanks. Is there a way to do it without defining a separate function like plusPlus ?

On Jan 28, 2017, at 10:43, Francesco Ariis wrote:

On Sat, Jan 28, 2017 at 10:09:10AM +0100, sasa bogicevic wrote:

...

Ok so how would the implementation look to get the correct result ? I can't seem to write something that will compile except ZipList version.

One way is by implementing your own (++):

data List a = Nil | Cons a (List a) deriving (Eq, Show)

plusPlus :: List a -> List a -> List a plusPlus Nil bs = bs plusPlus (Cons a as) bs = Cons a (as `plusPlus` bs)

instance Functor List where fmap f Nil = Nil fmap f (Cons a b) = Cons (f a) (fmap f b)

instance Applicative List where pure x = Cons x Nil Nil <*> _ = Nil _ <*> Nil = Nil (Cons x xy) <*> ys = (fmap x ys) `plusPlus` (xy <*> ys)

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