xml -导管解析xml属性。

Question

使用xml-conduit解析XML时，我偶然发现了以下问题:当我有多个属性时，具有相同的基名，但前缀不同，只按(词法)顺序排列。

如果同时存在一个属性的前缀版本和非前缀版本，那么如何获得前缀值？

最小非工作示例：

Main.hs

{-# LANGUAGE OverloadedStrings #-}

module Main where

import           Data.Text.Lazy (Text)
import qualified Data.Text.Lazy as T
import           Text.XML (parseText, def, elementAttributes, documentRoot)
import           Data.List (splitAt, drop)

main :: IO ()
main = do
  putStrLn "Example1: only the first element is parsed"
  putStrLn "========\n"
  print $ elementAttributes . documentRoot <$> parseText def (T.unlines test)
  putStrLn "Example2: this behaviour is independent of both having a prefix"
  putStrLn "========\n"
  print $ elementAttributes . documentRoot <$> parseText def (T.unlines $ dropAt 1 test)
  putStrLn "Example3: also no difference if there is just one attribute with prefix"
  putStrLn "========\n"
  print $ elementAttributes . documentRoot <$> parseText def (T.unlines $ dropAt 2 test)
  putStrLn "Example4: on its own the last element can be parsed"
  putStrLn "========\n"
  print $ elementAttributes . documentRoot <$> parseText def (T.unlines $ dropAt 1 $ dropAt 1 test)
  putStrLn "==============="
  putStrLn "Example1: it is always the first element parsed"
  putStrLn "========\n"
  print $ elementAttributes . documentRoot <$> parseText def (T.unlines test2)
  putStrLn "Example2: really just the first"
  putStrLn "========\n"
  print $ elementAttributes . documentRoot <$> parseText def (T.unlines $ dropAt 1 test2)


test :: [Text]
test =["<Root"
      ,  "here    = \"ok\""
      ,  "is:here = \"ok\""
      ,  "not:here=\"nok\">"
      ,"</Root>"]

test2 :: [Text]
test2 =["<Root"
       ,  "is:here = \"ok\""
       ,  "here    = \"ok\""
       ,  "not:here=\"nok\">"
       ,"</Root>"]

dropAt :: Int -> [a] -> [a]
dropAt i xs = let (hd,tl) = splitAt i xs
              in hd ++ drop 1 tl

attr.cabal

build-depends: base >= 4.7 && < 5
             , xml-conduit
             , text

> stack exec attr
Example1: only the first element is parsed
========

Right (fromList [(Name {nameLocalName = "here", nameNamespace = Nothing, namePrefix = Nothing},"ok")])
Example2: this behaviour is independent of both having a prefix
========

Right (fromList [(Name {nameLocalName = "here", nameNamespace = Nothing, namePrefix = Just "is"},"ok")])
Example3: also no difference if there is just one attribute with prefix
========

Right (fromList [(Name {nameLocalName = "here", nameNamespace = Nothing, namePrefix = Nothing},"ok")])
Example4: on its own the last element can be parsed
========

Right (fromList [(Name {nameLocalName = "here", nameNamespace = Nothing, namePrefix = Just "not"},"nok")])
===============
Example1: only the first element is parsed
========

Right (fromList [(Name {nameLocalName = "here", nameNamespace = Nothing, namePrefix = Just "is"},"ok")])
Example2: this behaviour is independent of both having a prefix
========

Right (fromList [(Name {nameLocalName = "here", nameNamespace = Nothing, namePrefix = Nothing},"ok")])

Answer 1

引用Text.XML.Name

前缀在语义上并不重要；它们被包括进来只是为了简化传递解析。当将名称与Eq或Ord方法进行比较时，前缀将被忽略。

语义差异在于名称空间，因此以下内容解决了您的问题：

test :: [Text]
test =["<Root xmlns:is=\"http://example.com\" xmlns:not=\"http://example.com/2\""
      ,  "here    = \"ok\""
      ,  "is:here = \"ok\""
      ,  "not:here=\"nok\">"
      ,"</Root>"]

这也是有意义的，因为我们可以在不同的地方不同地命名相同的名称空间，但应该是相同的。我认为，如果不将名称空间与前缀相关联，那么使用前缀也是无效的XML。