我正在从
http://hackage.haskell.org/package/xml-conduit-1.1.0.9/docs/Text-XML-Stream-Parse.html解析修改后的XML
这是它的样子：
<?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>
如何获得每个人的名字和年龄列表？
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,解决在没有属性时如何解析(使用tagNoAttrs？)
{-# 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
首先：解析xml-conduit中的组合器在很长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.那就是说,让我们来看看你的例子.您的代码有两个问题：
>它无法正确处理XML名称空间.所有元素名称都在http://example.com命名空间中,您的代码需要反映这一点.
>解析组合器要求您考虑所有元素.他们不会自动跳过某些元素.
所以这是使用流API的实现,它获得了所需的结果：
{-# 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
这是使用游标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 #-}
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]
_ -> []
