On Tue, Oct 8, 2013 at 10:43 PM, Thiago Negri
data Queue a = Queue [a]
empty :: Queue a empty = Queue []
push :: a -> Queue a -> Queue a push a (Queue as) = Queue (a:as)
pop :: Queue a -> Maybe (a, Queue a) pop (Queue []) = Nothing pop (Queue (a:as)) = Just (a, Queue as)
This is not a queue! This is a stack, a Last In First Out structure. Queues are First In First Out. Here, I'll help you with the quickcheck instance: instance (CoArbitrary a, Arbitrary b) => Arbitrary (SP a b) where arbitrary = oneof [liftM2 Put arbitrary arbitrary, liftM Get arbitrary] Also, we need a dummy show: instance (Show a, Show b) => Show (SP a b) where show _ = error "SP a b: no show" The test you need to write is the following: prop_SP_first :: SP Int Int -> [(Int,Int)] -> Bool prop_SP_first f xs = x1 == x2 where -- your name is thiago and you WILL be cool once you've fixed your buggy code -- Kim-Ee