Question

为方便分析数据，我想使用一个库，代码如下：

data SomeType = A [String] Int | B | C Int deriving (Eq, Ord, Show)

main = do 
  let theData = A ["a", "b", "c"] 9 : C 3 : B : []
  putStr $ treeString theData -- `treeString` is the implied library function

会产生类似于以下内容的输出：

- A:
| - - a
| | - b
| | - c
| - 9
- C:
| - 3
- B

有这样的图书馆吗？或者也许是解决这个问题的更好方法？

Answer 1

Data.Tree具有类似格式的drawTree和drawForest函数，因此您可以编写一个函数将数据结构转换为Tree String，然后使用{{1} }。

drawTree

<强>输出：

import Data.Tree

data SomeType = A [String] Int | B | C Int deriving (Eq, Ord, Show)

toTree :: SomeType -> Tree String
toTree (A xs n) = Node "A" [Node "*" (map (flip Node []) xs), Node (show n) []]
toTree B        = Node "B" []
toTree (C n)    = Node "C" [Node (show n) []]

main = do 
  let theData = A ["a", "b", "c"] 9 : C 3 : B : []
  putStr $ drawTree (Node "*" (map toTree theData))

Answer 2

添加到hammar的答案。以下是如何进行Data.Tree的通用转换：

import Data.Tree
import Data.Generics
import Control.Applicative

dataTree = fix . genericTree
  where
    genericTree :: Data a => a -> Tree String
    genericTree = dflt `extQ` string
      where
        string x = Node x []
        dflt a = Node (showConstr (toConstr a)) (gmapQ genericTree a)
    fix (Node name forest)
      | name == "(:)" 
      , a : b : [] <- forest
        = Node "*" $ (fix a) : (subForest $ fix b)
      | otherwise = Node name $ fix <$> forest

但为了处理一个数据类型，它们必须有一个Data的实例，可以通过添加{-# LANGUAGE DeriveDataTypeable #-}编译指示并使类型派生自Typeable来轻松实现和Data一样：

data SomeType = A [String] Int | B | C Int | D [[String]] 
  deriving (Typeable, Data)

用于分析的数据树输出库

2 个答案: