如果在使用HXT在Haskell中解析RSS文件时标记丢失(If tag misses when parsing an RSS file in Haskell with HXT)

如果在使用HXT在Haskell中解析RSS文件时标记丢失(If tag misses when parsing an RSS file in Haskell with HXT)

我必须在Haskell中解析一个RSS文件，我做了类似的事情：

atTag tag = deep (isElem >>> hasName tag) getRSSDetails = atTag "channel" >>> proc p -> do fTitle <- gotoAndTake "title" -< p fLink <- gotoAndTake "link" -< p fDescription <- gotoAndTake "description" -< p fLanguage <- gotoAndTake "language" -< p fGenerator <- gotoAndTake "generator" -< p fCopyright <- gotoAndTake "copyright" -< p fWebMaster <- gotoAndTake "webMaster" -< p fLastBuildDate <- gotoAndTake "lastBuildDate" -< p where gotoAndTake a = (getChildren >>> isElem >>> hasName a >>> getChildren >>> getText)

我的问题是，当一个标签丢失时，让我们说RSS文件中的“lastBuildDate”比我得到一个空列表，但我只想用“”替换该项目。

我怎样才能做到这一点 ？？ 谢谢，

main = do rssFeeds <- runX (parseRSS "rss.xml" >>> getRSSDetails) print rssFeeds

EDIT1：通过在gotoAndTake a ...的末尾添加orElse （constA“”）来解决...

I have to parse an RSS file in Haskell and I do something like:

atTag tag = deep (isElem >>> hasName tag) getRSSDetails = atTag "channel" >>> proc p -> do fTitle <- gotoAndTake "title" -< p fLink <- gotoAndTake "link" -< p fDescription <- gotoAndTake "description" -< p fLanguage <- gotoAndTake "language" -< p fGenerator <- gotoAndTake "generator" -< p fCopyright <- gotoAndTake "copyright" -< p fWebMaster <- gotoAndTake "webMaster" -< p fLastBuildDate <- gotoAndTake "lastBuildDate" -< p where gotoAndTake a = (getChildren >>> isElem >>> hasName a >>> getChildren >>> getText)

My problem is that when one tag is missing, let's say "lastBuildDate" from the RSS file than I get an empty list, but I want just to replace that item with "".

How can I do that ?? Thanks,

main = do rssFeeds <- runX (parseRSS "rss.xml" >>> getRSSDetails) print rssFeeds

EDIT1: Solved by adding orElse (constA "") at the end of where gotoAndTake a ...

最满意答案

通过添加解决

orElse (constA "")

在......的最后

where gotoAndTake a = (getChildren >>> isElem >>> hasName a >>> getChildren >>> getText)

Solved by adding

orElse (constA "")

at the end of

where gotoAndTake a = (getChildren >>> isElem >>> hasName a >>> getChildren >>> getText)