从xml-conduit获取所有名称 [英] Get all Names from xml-conduit

问题描述

我从 http://hackage.haskell.org/package/xml-conduit-1.1.0.9/docs/Text-XML-Stream-Parse.html

下面是它的样子：

 <？xml version =1.0encoding =utf-8 ？> 
< population xmlns：xsd =http://www.w3.org/2001/XMLSchemaxmlns：xsi =http://www.w3.org/2001/XMLSchema-instancexmlns = http://example.com> 
< success> true< / success> 
< row_count> 2< / row_count> 
< summary> 
<香蕉> 0< /香蕉> 
< / summary> 
<人> 
< person> 
< firstname> Michael< / firstname> 
< age> 25< / age> 
< / person> 
< person> 
< firstname> Eliezer< / firstname> 
< age> 2< / age> 
< / person> 
< / people> 
< / population> 
  

如何获得 firstname 和 age 为每个人？

我的目标是使用http-conduit下载这个xml然后解析它，但我正在寻找一个解决方案，以便在没有属性的情况下解析（使用tagNoAttrs？）

这是我尝试过的，并且添加了我的Haskell评论中的问题：

  { - ＃LANGUAGE OverloadedStrings＃ - } 
 import Control.Monad.Trans.Resource 
 import Data.Conduit（（$$））
 import Data.Text（Text，unpack）
 import Text.XML.Stream.Parse 
 import Control.Applicative（（< ; *））
 
 data Person = Person Int Text 
导出显示
 
  - 是否需要将lambda函数\age更改为其他值才能获得姓名和年龄？ 
 parsePerson = tagNoAttrperson$ \age  - >做
名称<  - 内容 - 如何从内容中获得年龄？ unpack用于属性
返回$ Person年龄名称
 
 parsePeople = tagNoAttrpeople$ many parsePerson 
 
  - 这不会忽略xmlns属性
 parsePopulation = tagNamepopulation（optionalAttrxmlns< * ignoreAttrs）$ parsePeople 
 
 main = do 
 people<  -  runResourceT $ 
 parseFile def people2.xml$$ parsePopulation 
 print people 
  

解决方案

<首先：解析xml-conduit中的组合器在一段时间内没有更新，并显示它们的年龄。我建议大多数人使用DOM或游标界面。这就是说，让我们看看你的例子。你的代码有两个问题：

• 它没有正确处理XML名称空间。所有元素名称都位于 http://example.com 命名空间中，并且您的代码需要反映它。


• 解析组合器要求您考虑所有元素。他们不会自动跳过一些元素给你。
/ b>



  { - ＃LANGUAGE OverloadedStrings＃ - } 
 import Control.Monad.Trans.Resource（runResourceT）
 import Data.Conduit（Consumer，（$$））
 import Data.Text（Text）
 import Data.Text.Read（decimal）
 import Data.XML.Types（Event）
 import Text.XML.Stream.Parse 
 
 data Person = Person Int Text 
导出显示
 
  - 是否需要更改lambda函数\\为了获得名称和年龄，还需要别的东西？ 
 parsePerson :: MonadThrow m =>消费者事件m（可能是人）
 parsePerson = tagNoAttr{http://example.com} person$ do 
 name<  -  force名字标记缺失$ tagNoAttr{http：// example.com}名字内容
 ageText<  - 强制缺少时间标记$ tagNoAttr{http://example.com}年龄内容
小数
小数ageText右（年龄，） - >返回$人年龄名称
 _  - >强制无效年龄值$ return Nothing 
 
 parsePeople :: MonadThrow m => Consumer Event m [Person] 
 parsePeople = forceno people tag$ do 
 _<  -  tagNoAttr{http://example.com} successcontent 
 _<  - tagNoAttr{http://example.com} row_countcontent 
 _<  -  tagNoAttr{http://example.com}摘要$ 
 tagNoAttr{http://example.com } bananascontent 
 tagNoAttr{http://example.com} people$ many parsePerson 
 
  - 这不会忽略xmlns属性
 parsePopulation :: MonadThrow m =>消费者事件m [Person] 
 parsePopulation =强制缺少人口标签$ 
 tagName{http://example.com} populationignoreAttrs $ \（） - > parsePeople 
 $ b $ main main :: IO（）
 main = do 
 people<  -  runResourceT $ 
 parseFile defpeople2.xml$$ parsePopulation 
打印人员
  

以下是使用游标API的示例。请注意，它具有不同的错误处理特性，但对于格式良好的输入应该产生相同的结果。

  { - ＃LANGUAGE OverloadedStrings ＃ - } 
导入Text.XML 
导入Text.XML.Cursor 
导入Data.Text（文本）
导入Data.Text.Read（十进制）
导入Data.Monoid（mconcat）
 
 main :: IO（）
 main = do 
 doc<  -  Text.XML.readFile defpeople2.xml
 let cursor = fromDocument doc 
 print $ cursor $ // element{http://example.com} person> => parsePerson 
 
 data Person = Person Int Text 
派生Show 
 
 parsePerson :: Cursor  - > [Person] 
 parsePerson c = do 
 let name = c $ / element{http://example.com} firstname& / content 
 ageText = c $ / element{ http://example.com} age& / content 
 case decimal $ mconcat ageText 
 Right（age，） - > [人年龄$ mconcat名称] 
 _  - > [] 
  




I'm parsing a modified XML from http://hackage.haskell.org/package/xml-conduit-1.1.0.9/docs/Text-XML-Stream-Parse.html

Here's what it looks like:

<?xml version="1.0" encoding="utf-8"?>
<population xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://example.com">
  <success>true</success>
  <row_count>2</row_count>
  <summary>
    <bananas>0</bananas>
  </summary>
  <people>
      <person>
          <firstname>Michael</firstname>
          <age>25</age>
      </person>
      <person>
          <firstname>Eliezer</firstname>
          <age>2</age>
      </person>
  </people>
</population>

How do I get a list of firstname and age for every person?

My goal is to use http-conduit to download this xml and then parse it, but I am looking for a solution on how to parse when there are no attributes (use tagNoAttrs?)

Here's what I've tried, and I've added my questions in the Haskell comments:

{-# LANGUAGE OverloadedStrings #-}
import Control.Monad.Trans.Resource
import Data.Conduit (($$))
import Data.Text (Text, unpack)
import Text.XML.Stream.Parse
import Control.Applicative ((<*))

data Person = Person Int Text
        deriving Show

-- Do I need to change the lambda function \age to something else to get both name and age?
parsePerson = tagNoAttr "person" $ \age -> do
        name <- content  -- How do I get age from the content?  "unpack" is for attributes
        return $ Person age name

parsePeople = tagNoAttr "people" $ many parsePerson

-- This doesn't ignore the xmlns attributes
parsePopulation  = tagName "population" (optionalAttr "xmlns" <* ignoreAttrs) $ parsePeople

main = do
        people <- runResourceT $
             parseFile def "people2.xml" $$ parsePopulation
        print people

解决方案

Firstly: parsing combinators in xml-conduit haven't been updated in quite a while, and show their age. I recommend most people to use the DOM or cursor interface instead. That said, let's look at your example. There are two problems with your code:

• It doesn't properly handle XML namespaces. All of the element names are in the http://example.com namespace, and your code needs to reflect that.
• The parsing combinators demand that you account for all elements. They won't automatically skip over some elements for you.

So here's an implementation using the streaming API that gets the desired result:

{-# LANGUAGE OverloadedStrings #-}
import           Control.Monad.Trans.Resource (runResourceT)
import           Data.Conduit                 (Consumer, ($$))
import           Data.Text                    (Text)
import           Data.Text.Read               (decimal)
import           Data.XML.Types               (Event)
import           Text.XML.Stream.Parse

data Person = Person Int Text
        deriving Show

-- Do I need to change the lambda function \age to something else to get both name and age?
parsePerson :: MonadThrow m => Consumer Event m (Maybe Person)
parsePerson = tagNoAttr "{http://example.com}person" $ do
        name <- force "firstname tag missing" $ tagNoAttr "{http://example.com}firstname" content
        ageText <- force "age tag missing" $ tagNoAttr "{http://example.com}age" content
        case decimal ageText of
            Right (age, "") -> return $ Person age name
            _ -> force "invalid age value" $ return Nothing

parsePeople :: MonadThrow m => Consumer Event m [Person]
parsePeople = force "no people tag" $ do
    _ <- tagNoAttr "{http://example.com}success" content
    _ <- tagNoAttr "{http://example.com}row_count" content
    _ <- tagNoAttr "{http://example.com}summary" $
        tagNoAttr "{http://example.com}bananas" content
    tagNoAttr "{http://example.com}people" $ many parsePerson

-- This doesn't ignore the xmlns attributes
parsePopulation :: MonadThrow m => Consumer Event m [Person]
parsePopulation = force "population tag missing" $
    tagName "{http://example.com}population" ignoreAttrs $ \() -> parsePeople

main :: IO ()
main = do
        people <- runResourceT $
             parseFile def "people2.xml" $$ parsePopulation
        print people

Here's an example using the cursor API. Note that it has different error handling characteristics, but should produce the same result for well-formed input.

{-# LANGUAGE OverloadedStrings #-}
import Text.XML
import Text.XML.Cursor
import Data.Text (Text)
import Data.Text.Read (decimal)
import Data.Monoid (mconcat)

main :: IO ()
main = do
    doc <- Text.XML.readFile def "people2.xml"
    let cursor = fromDocument doc
    print $ cursor $// element "{http://example.com}person" >=> parsePerson

data Person = Person Int Text
        deriving Show

parsePerson :: Cursor -> [Person]
parsePerson c = do
    let name = c $/ element "{http://example.com}firstname" &/ content
        ageText = c $/ element "{http://example.com}age" &/ content
    case decimal $ mconcat ageText of
        Right (age, "") -> [Person age $ mconcat name]
        _ -> []

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