Question

我希望实例显示我的二叉树的功能，以这种方式构建：data Tree a = Nil | Leaf a | Branch a (Tree a) (Tree a)。我希望获得像＃tree; tree＆＃34; unix命令。例如：

显示功能如下：

> 27
>> 14
>>> 10

>>> 19

>> 35
>>> 31

>>> 42

我想列出每个＆＃34;子树＆＃34;具有递归功能但我不知道这是我的实际代码：

instance (Show a)=>Show (Tree a) where
show Nil = ""
show (Leaf e) = show e
show (Branch e ls rs) = show e ++ "\n\t" ++ show ls ++ "\n\t" ++ show rs

所以问题是：我如何实现递归制表功能，因为每次我使用新行并仅制表一次而不是子树深度

Answer 1

你可以定义一个辅助函数，我们这样称它为showWithDepth：

showWithDepth :: (Show a) => Tree a -> Int -> String
showWithDepth Nil _ = ""
showWithDepth (Leaf e) depth = (replicate depth '\t') ++ show e ++ "\n"
showWithDepth (Branch e ls rs) depth = (replicate depth '\t') ++ show e ++ "\n" ++ showWithDepth ls (depth+1) ++ showWithDepth rs (depth+1)

现在我们可以简单地定义你的实例：

instance (Show a)=>Show (Tree a) where
show x = showWithDepth x 0

实例在haskell中显示树

1 个答案: