It's working now! Thanks very much.

Haha, left isNothing in from debugging it months ago :) Completely useless now thankfully

Your first haskell test case is wrong. The tree looks like this

2

8   3

9 1 4 5
(Just (TreeNode {

left = Just (TreeNode

{left = Just (TreeNode

{left = Nothing,

right = Nothing,

value = 9}),

right = Just (TreeNode

{left = Nothing,

right = Nothing,

value = 1}),

value = 8}),

right = Just (TreeNode

{left = Just (TreeNode

{left = Nothing,

right = Nothing,

value = 4}),

right = Just (TreeNode

{left = Nothing,

right = Nothing,

value = 5}),

value = 3}),

value = 2}))

manhattanDistance( [1, 1], [1, 1] ) => returns 0

should be manhattanDistance (1,1) (1,1)
etc.