Haskell中的堆运动

Question

I've got this exercise where I've got to remove the minimum element from a Heap and return a tuple with (a,b) where a = the element removed and b = the new Heap.

So where's my code

removeMin :: Ord a => Heap a -> (a, Heap a)
removeMin (Node r (Node a b c) (Node x y z)) = (r, newHeap (Node a b c) (Node x y z))
  where
    newHeap Empty Empty = Empty
    newHeap h Empty = h
    newHeap Empty h = h
    newHeap (Node a b c) (Node x y z) = (Node (min a x) (newHeap b c) (newHeap y z))

And I get this error code

No instance for (Show (Heap a0)) arising from a use of ‘print’
In the first argument of ‘print’, namely ‘it’
In a stmt of an interactive GHCi command: print it

when I try to do something like this

 removeMin (Node 2 (Node 5 (Node 7 Empty Empty) (Node 9 Empty Empty)) (Node 10 (Node 13 Empty Empty) (Node 15 Empty Empty)))

This might be an easy problem, but I'm in my first year of Computer Science and Haskell is my first real coding experience so I'm sorry to bother with such simples questions, but I really appreciate the help.

Answer 1

Here you go:

instance (Show a) => Show (Heap a) where
    show (Empty) = "Empty"
    show (Node x a b) = ("Node ") ++ show x ++ (" (") ++ show a ++ (") ") ++ ("(") ++ show b ++ (")")

removeMin :: Ord a => Heap a -> (a,Heap a)
removeMin (Node a e d) = (a,build e d) where
    build (Node a e d) (Node b e2 d2)
        | (a < b) = (Node a (build e d) (Node b e2 d2))
        | otherwise = (Node b (Node a e d) (build e2 d2))
    build a Empty = a
    build Empty b = b

JBB is your friend