Haskell语言学习笔记（76）Data.Tree

Data.Tree

data Tree a = Node {

        rootLabel :: a,

        subForest :: Forest a

    } deriving (Eq, Read, Show)

type Forest a = [Tree a]

Data.Tree 是一种非空（存在根节点），可以有无限分支，每个节点均可有多路分支的Tree类型。

Prelude Data.Tree> :t Node 1

Node 1 :: Num a => Forest a -> Tree a

Prelude Data.Tree> a = Node 1 [Node 2 [], Node 3 []]

Prelude Data.Tree> a

Node {rootLabel = 1, subForest = [Node {rootLabel = 2, subForest = []},Node {rootLabel = 3, subForest = []}]}

Prelude Data.Tree> putStr $ drawTree $ fmap show a

1

|

+- 2

|

`- 3

Prelude Data.Tree> foldTree (\x xs -> sum (x:xs)) a

6

Prelude Data.Tree> foldTree (\x xs -> maximum (x:xs)) a

3

Prelude Data.Tree> tree = Node "A" [Node "B" [], Node "C" [Node "D" [], Node "E" []]]

Prelude Data.Tree> print tree

Node {rootLabel = "A", subForest = [Node {rootLabel = "B", subForest = []},Node {rootLabel = "C", subForest = [Node {rootLabel = "D", subForest = []},Node {rootLabel = "E", subForest = []}]}]}

Prelude Data.Tree> putStr $ drawTree tree

A

|

+- B

|

`- C

   |

   +- D

   |

   `- E

Prelude Data.Tree> putStr $ drawForest $ subForest tree

B

C

|

+- D

|

`- E

Prelude Data.Tree> flatten tree

["A","B","C","D","E"]

Prelude Data.Tree> levels tree

[["A"],["B","C"],["D","E"]]

实例