I have a question about what's the idiomatic way to walk a tree where there is also a requirement
for pattern-matching to draw variables out of the Node 'container':
module Test
where
data Tree a b = EmptyTree | Node a b [Tree a b]
deriving (Show, Read, Eq)
t = Node "goal" 1.0 [
Node "c1" 0.5 [
Node "c3" 3.0 [
Node "c5" 1.0 []
]
],
Node "c2" 0.5 [
Node "c4" 2.0 []
]
]
sumTree :: (Num b) => Tree a b -> b
sumTree EmptyTree = 0
sumTree (Node _ value []) = value
sumTree (Node _ value [x]) = value + sumTree x
sumTree (Node name value (x:xs)) = value + sumTree x + sumTree (Node name 0 xs)
depth :: Tree a b -> Int
depth EmptyTree = 0
depth (Node _ _ []) = 1
depth (Node _ _ [x]) = 1 + depth x
depth (Node n v (x:xs)) = 1 + depth (Node n v xs)
Interactively:
*Test> sumTree t
8.0
*Test> depth t
4
*Test>
This seems to work, but I have a sense that one should use folds and fmap and that there
is a better and cleaner what to do this.
Any help would be much appreciated.
Thanks
AK
