xml - 如何使用Haskell(使用HaXml)访问一些XML数据？

我想访问XML文件的数据，例如

<?xml version="1.0"?>
<MY>
  <Foo id="1" name="test">
    <Argument name="a" />
  </Foo>
  <Foo id="2" name="test2">
    <Argument name="a" />
    <Argument name="b" />
  </Foo>
  <Other id="2" name="someOther"/>
</MY>

我想要例如要读出每个Foo的参数，我该如何用Haskell做到这一点？ (我想使用HaXml模块)

我不知道从哪里开始。

最佳答案

我找不到haXml的最新文档和示例。

但是，有一些有关HXT的文档。
我知道这对于您的示例来说可能是一个过大的杀伤力，但是无论如何。

如果要使用tagsoup，则以下答案可能会有所帮助:
xml-tree parser (Haskell) for graph-library
In Haskell how do you extract strings from an XML document?

以下是HXT的示例文档:
http://www.haskell.org/haskellwiki/HXT/Conversion_of_Haskell_data_from/to_XML
http://www.haskell.org/haskellwiki/HXT
http://www.haskell.org/haskellwiki/HXT/Practical
http://en.wikibooks.org/wiki/Haskell/XML

现在，代码使用HXT。
(警告我不确定这是否正确)

我遵循了该教程:
http://www.haskell.org/haskellwiki/HXT/Conversion_of_Haskell_data_from/to_XML

您需要将您的xml文件作为“data.xml”

import Data.Map (Map, fromList, toList)
import Text.XML.HXT.Core


type Foos = Map String [Foo]

data Foo = Foo
     {
       fooId :: String
     , fooName :: String
     , arguments :: [Argument]
     }
          deriving (Show, Eq)



data Argument = Argument
      { argName  :: String
      }
           deriving (Show, Eq)

instance XmlPickler Foo where
  xpickle = xpFoo


instance XmlPickler Argument where
  xpickle = xpArgument

-- WHY do we need this?? no clue
instance XmlPickler Char where
    xpickle = xpPrim

-- this could be wrong
xpFoos :: PU Foos
xpFoos
  = xpWrap (fromList
          , toList
          ) $
  xpList $
      xpElem "MY" $
      xpickle

xpFoo :: PU Foo
xpFoo
  = xpElem "Foo" $
     xpWrap ( uncurry3 Foo
            , \ f -> (fooId f
                      , fooName f
                      , arguments f
                     )
           ) $
    xpTriple (xpAttr "id" xpText)
              (xpAttr "name" xpText)
              (xpList xpickle)


xpArgument :: PU Argument
xpArgument
    = xpElem "Argument" $
       xpWrap ( \ ((a)) -> Argument a
               , \ t -> (argName t)
              ) $
       (xpAttr "name" xpText )


main    :: IO ()
main
     = do
       runX ( xunpickleDocument xpFoos
                                [ withValidate no
                                , withTrace 1
                                , withRemoveWS yes
                                , withPreserveComment no
                                ] "data.xml"
         >>>
             arrIO ( \ x -> do {print x ; return x})
            )
       return ()

结果(您需要将XML示例作为“data.xml”):

-- (1) getXmlContents
-- (1) readDocument: "data.xml" (mime type: "text/xml" ) will be processed
-- (1) readDocument: "data.xml" processed
fromList [("",[Foo {fooId = "1", fooName = "test", arguments = [Argument {argName = "a"}]},
Foo {fooId = "2", fooName = "test2", arguments = [Argument {argName = "a"},
Argument     {argName = "b"}]}])]