never executed always true always false

    1 module ElmFormat.AST.PublicAST.MaybeF where
    2 
    3 
    4 import Data.Coapplicative
    5 data MaybeF f a
    6     = JustF (f a)
    7     | NothingF a
    8     deriving (Functor)
    9 
   10 instance Prelude.Foldable f => Prelude.Foldable (MaybeF f) where
   11     foldMap f (JustF fa) = Prelude.foldMap f fa
   12     foldMap f (NothingF a) = f a
   13 
   14 instance Traversable f => Traversable (MaybeF f) where
   15     traverse f (JustF fa) = JustF <$> traverse f fa
   16     traverse f (NothingF a) = NothingF <$> f a
   17 
   18 instance Coapplicative f => Coapplicative (MaybeF f) where
   19     extract (JustF fa) = extract fa
   20     extract (NothingF a) = a
   21 
   22 maybeF :: (a -> x) -> (f a -> x) -> MaybeF f a -> x
   23 maybeF fromA _ (NothingF a) = fromA a
   24 maybeF _ fromFa (JustF fa) = fromFa fa