用于图库的xml树分析器（Haskell） [英] xml-tree parser (Haskell) for graph-library

问题描述

我正在写图库来处理图形。
主要任务 - 解析xml树。
该树看起来像

 < graph nodes = 4 arcs = 5> 
< node id = 1 /> 
< node id = 2 /> 
< node id = 3 /> 
< node id = 4 /> 
< arc from = 1 to = 2 /> 
< arc from = 1 to = 3 /> 
< arc from = 1 to = 4 /> 
< arc from = 2 to = 4 /> 
< arc from = 3 to = 4 /> 
< /图表> 
  

存储结构：

  type Id = Int 
 
 data Node =节点Id派生（显示）
数据Arc =弧Id Id派生（显示）
 
 data Graph = Graph {nodes :: [Node]，
 arcs :: [Arc]} 
  

如何将xml文件中的数据写入此结构？
我无法为这种类型的xml树（HXT库）编写解析器。假设您将这个解析器转换为转换为正确的XML（用引号包围所有的属性值），下面的代码可以工作（使用xml-enumerator）：

  { - ＃LANGUAGE OverloadedStrings＃ - } 
 import Text.XML.Enumerator.Parse 
 import Control.Monad 
 import Data.Text（unpack）
 import Control.Applicative 
 
类型Id = Int 
 
数据节点=节点Id派生（显示）
数据Arc =弧Id Id导出（显示）
 
数据图=图{nodes：[Node]，
 arcs :: [Arc]} 
导出显示
 
 main = parseFile_graph.xmldecodeEntities $ force图形需要parseGraph 
 
 parseGraph = tagNamegraphgetCounts $ \（nodeCount，arcCount） - > do 
节点<  -  replicateM nodeCount parseNode 
 arcs<  -  replicateM arcCount parseArc 
 return $图形节点arcs 
其中
 requireNum name = do 
x< ;  -  requireAttr name 
 case reads $ $ unpack x of 
（i，_）：_  - >返回i 
 _  - >失败$无效整数：++解包x 
 getCounts = do 
n<  -  requireNum节点
a<  -  requireNum弧形
 return（n，a） 
 parseNode = forcenode required$ tagNamenode
（Node< $> requireNumid）return 
 parseArc = forcearc required$ tagNamearc
（Arc< $> requireNumfrom<> requireNum到）返回
  

输出：

 图形{nodes = [节点1，节点2，节点3，节点4]，弧形= [弧1 2，弧1 3，弧1 4，弧2 4，弧3 4]} 
  

I'm writing a library for working with graphs. The primary task - parsing xml-tree. The tree looks like

<graph nodes=4 arcs=5>
    <node id=1 />
    <node id=2 />
    <node id=3 />
    <node id=4 />
    <arc from=1 to=2 />
    <arc from=1 to=3 />
    <arc from=1 to=4 />
    <arc from=2 to=4 />
    <arc from=3 to=4 />
</graph>

Structure for storing:

type Id = Int

data Node = Node Id deriving (Show)
data Arc = Arc Id Id deriving (Show)

data Graph = Graph { nodes :: [Node],
             arcs  :: [Arc]}

How to write data from the xml file into this structure? I can not write a parser for xml tree of this kind (HXT library)

解决方案

Assuming that you convert that into proper XML (surround all the attribute values with quotes), the following code will work (using xml-enumerator):

{-# LANGUAGE OverloadedStrings #-}
import Text.XML.Enumerator.Parse
import Control.Monad
import Data.Text (unpack)
import Control.Applicative

type Id = Int

data Node = Node Id deriving (Show)
data Arc = Arc Id Id deriving (Show)

data Graph = Graph { nodes :: [Node],
             arcs  :: [Arc]}
  deriving Show

main = parseFile_ "graph.xml" decodeEntities $ force "graph required" parseGraph

parseGraph = tagName "graph" getCounts $ \(nodeCount, arcCount) -> do
    nodes <- replicateM nodeCount parseNode
    arcs <- replicateM arcCount parseArc
    return $ Graph nodes arcs
  where
    requireNum name = do
        x <- requireAttr name
        case reads $ unpack x of
            (i, _):_ -> return i
            _ -> fail $ "Invalid integer: " ++ unpack x
    getCounts = do
        n <- requireNum "nodes"
        a <- requireNum "arcs"
        return (n, a)
    parseNode = force "node required" $ tagName "node"
        (Node <$> requireNum "id") return
    parseArc = force "arc required" $ tagName "arc"
        (Arc <$> requireNum "from" <*> requireNum "to") return

Outputs:

Graph {nodes = [Node 1,Node 2,Node 3,Node 4], arcs = [Arc 1 2,Arc 1 3,Arc 1 4,Arc 2 4,Arc 3 4]}

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