Finds the count of all interesting nodes in a binary tree (i.e. count of all nodes which has value equal to the count of their children)

interesting-nodes.hs

data Tree = Nil | Node Int Tree Tree deriving (Eq)

interestingNodesCount Nil = 0
interestingNodesCount (Node a Nil Nil) = if a == 0 then 1 else 0
interestingNodesCount (Node a left right)
    | left /= Nil && right == Nil && a == 1   =   1 + interestingNodesCount left
    | left == Nil && right /= Nil && a == 1   =   1 + interestingNodesCount right
    | left /= Nil && right == Nil && a /= 1   =   0 + interestingNodesCount left
    | left == Nil && right /= Nil && a /= 1   =   0 + interestingNodesCount right
    | otherwise                               =   (if a == 2 then 1 else 0) + (interestingNodesCount left) + (interestingNodesCount right)
--    | left /= Nil && right /= Nil && a == 2   =   1 + (interestingNodesCount left) + (interestingNodesCount right)
--    | left /= Nil && right /= Nil && a /= 2   =   0 + (interestingNodesCount left) + (interestingNodesCount right)