# Pastebin nqt2N6lQ
Im trying to obtain the min element in a tree using the following definition:
data Tree a 
    = Tip
    | Bin (Tree a) a (Tree a)
    deriving (Show, Eq)


foldTree :: (b -> a -> b -> b) -> b -> Tree a -> b
foldTree f z Tip         = z
foldTree f z (Bin l x r) = f (foldTree f z l) x (foldTree f z r)

minTree :: (Ord a) => Tree a -> Maybe a
minTree = foldTree f z
    where
    f l x r = minimum [l, Just x, r]
    z = Nothing
However not quite sure how to obtain something other than Nothing as an output? Anyone have suggestions?