如何使用Haskell的xml-conduit解析GPX文件？ [英] How to parse GPX file using Haskell's xml-conduit?

问题描述

我想用 xml-conduit 来解析GPX文件。到目前为止，我已经得到了以下内容：

  { - ＃LANGUAGE OverloadedStrings＃ - } 
 
 import Control.Applicative 
导入Data.Text作为T 
导入Text.XML 
导入Text.XML.Cursor 
 
数据Trkpt = Trkpt {
 trkptLat： ：Text，
 trkptLon :: Text，
 trkptEle :: Text，
 trkptTime :: Text 
}派生（显示）
 
 trkptsFromFile path = 
 gpxTrkpts。 fromDocument< $> Text.XML.readFile def path 
 
 gpxTrkpts = 
 child> =>元素{http://www.topografix.com/GPX/1/0}trk> => 
 child> =>元素{http://www.topografix.com/GPX/1/0}trkseg> => 
 child> =>元素{http://www.topografix.com/GPX/1/0}trkpt> => 
 child> => \e  - > do 
 let ele = T.concat $ element{http://www.topografix.com/GPX/1/0}elee>> = descendant>> = content 
 let time = T.concat $ element{http://www.topografix.com/GPX/1/0}timee>> = descendant>>> = content 
 let lat = T. concat $ attributelate 
 let lon = T.concat $ attributelone 
 return $ Trkpt lat lon ele time time 
  

示例GPX文件为此处。

虽然原始的GPX文件数据都是有效的，但我得到了奇怪的结果，其中解析的文本大部分是空的，有一些零星的实际值。当有实际值时，它只在记录的一个字段中。

我很确定我没有使用 xml-conduit API。我在做什么错了？

解决方案

两个问题。首先，名称空间中存在拼写错误;它应该是 http://www.topografix.com/GPX/1/1 。其次，你最后的Kleisli箭头（ \e-> do - etc。）正在处理 trkpt 元素，而不是在 trkpt 本身。这是一个 gpxTrkpts ，它应该做你想做的：

  gpxTrkpts = 
 child> =>元素{http://www.topografix.com/GPX/1/1}trk> => 
 child> =>元素{http://www.topografix.com/GPX/1/1}trkseg> => 
 child> =>元素{http://www.topografix.com/GPX/1/1}trkpt> => 
 \e  - > do 
 let cs = child e 
 ele = T.concat $ cs>> = element{http://www.topografix.com/GPX/1/1}ele>>> ; =后代>> =内容
时间= T.concat $ cs>> =元素{http://www.topografix.com/GPX/1/1}time>> =后代>> =内容
 lat = T.concat $属性late 
 lon = T.concat $属性lone 
返回$ Trkpt lat lon ele时间
  

I'd like to use xml-conduit to parse GPX files. So far I've got the following:

{-# LANGUAGE OverloadedStrings #-}

import Control.Applicative
import Data.Text           as T
import Text.XML
import Text.XML.Cursor

data Trkpt = Trkpt {
  trkptLat :: Text,
  trkptLon :: Text,
  trkptEle :: Text,
  trkptTime :: Text
  } deriving (Show)

trkptsFromFile path =
  gpxTrkpts . fromDocument <$> Text.XML.readFile def path

gpxTrkpts =
  child >=> element "{http://www.topografix.com/GPX/1/0}trk" >=>
  child >=> element "{http://www.topografix.com/GPX/1/0}trkseg" >=>
  child >=> element "{http://www.topografix.com/GPX/1/0}trkpt" >=>
  child >=> \e -> do
    let ele  = T.concat $ element "{http://www.topografix.com/GPX/1/0}ele" e >>= descendant >>= content
    let time = T.concat $ element "{http://www.topografix.com/GPX/1/0}time" e >>= descendant >>= content
    let lat  = T.concat $ attribute "lat" e
    let lon  = T.concat $ attribute "lon" e
    return $ Trkpt lat lon ele time

A sample GPX file is here.

I'm getting strange results where the parsed text is mostly empty, with some sporadic actual values, although the original GPX file data is all valid. When there is an actual value, it is only in one of the fields of the record.

I'm quite certain I'm not using the xml-conduit API properly. What am I doing wrong?

解决方案

Two issues. Firstly, there is a typo in the namespace; it should be http://www.topografix.com/GPX/1/1. Secondly, your final Kleisli arrow (\e -> do -- etc.) is acting on the children of the trkpt elements, rather than on the trkpt themselves. Here is a gpxTrkpts which should do what you want:

gpxTrkpts =
  child >=> element "{http://www.topografix.com/GPX/1/1}trk" >=>
  child >=> element "{http://www.topografix.com/GPX/1/1}trkseg" >=>
  child >=> element "{http://www.topografix.com/GPX/1/1}trkpt" >=>
  \e -> do
    let cs = child e
        ele  = T.concat $ cs >>= element "{http://www.topografix.com/GPX/1/1}ele" >>= descendant >>= content
        time = T.concat $ cs >>= element "{http://www.topografix.com/GPX/1/1}time" >>= descendant >>= content
        lat  = T.concat $ attribute "lat" e
        lon  = T.concat $ attribute "lon" e
    return $ Trkpt lat lon ele time

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