如何将二叉树的字符串表示读回树中？

Question

我有以下代码接受输入作为 ex 中给出的示例并创建具有给定类型的树：

data QA = Leaf String | Question QA String QA

ex :: QA
ex = (Question 
       (Question (Leaf "Marie Curie") "Is she a scientist?" (Leaf "Queen Elisabeth II"))
       "Is she from Europe?"
       (Question (Leaf "Marilyn Monroe") "Is she an actress?" (Leaf "Hilary Clinton")))

showQa :: QA -> String 
showQa (Leaf x) = "(" ++ x ++ ")"
showQa (Question left x right) = "(" ++ x ++ showQa left ++ showQa right ++ ")"

instance Show QA where
  show = showQa

然后我使用 showQa 函数将树转换为字符串，以便能够将其存储在文件中，并以字符串形式输出以下内容：

"(Is she from Europe?(Is she a scientist?(Marie Curie)(Queen Elisabeth II))(Is she an actress?(Marilyn Monroe)(Hilary Clinton)))"

问题是当我再次从文件中读取字符串时，如何将这个字符串转换为原始类型的原始树。

Answer 1

使 QA 成为展示和阅读的实例

data QA = Leaf String | Question QA String QA deriving (Show, Read)

您可以通过这种方式摆脱 showQa，只调用 QA 类型上的 show。读书也一样。

在写入文件时您可以

writeFile "[FileName].qa" (show ex)

“ex”应该是 QA 类型的名称，在您的情况下它被称为 ex

从文件中读取你可以只使用 readFile 并读取结果：

fileReader = do
    content <- tryIOError (readFile "[FileName].qa")
    case content of
        Left e  -> do
            return (ex) --In case of reading file goes wrong
        Right r -> do 
            return (read r)

如何将二叉树的字符串表示读回树中？

How to read a string representation of a binary tree back into the tree?

tree

binary-tree

haskell

functional-programming