In Haskell how do you extract strings from an XML document?

I've never actually bothered to figure out how to extract bits out of XML documents using HaXML; HXT has met all my needs.

{-# LANGUAGE Arrows #-}import Data.Maybeimport Text.XML.HXT.Arrowtype Name = Stringtype Value = Stringdata LocalizedString = LS Name ValuegetLocalizedStrings :: String -> Maybe [LocalizedString]getLocalizedStrings = (.) listToMaybe . runLA $ xread >>> getRootatTag :: ArrowXml a => String -> a XmlTree XmlTreeatTag tag = deep $ isElem >>> hasName taggetRoot :: ArrowXml a => a XmlTree [LocalizedString]getRoot = atTag "root" >>> listA getElemgetElem :: ArrowXml a => a XmlTree LocalizedStringgetElem = atTag "elem" >>> proc x -> do    name <- getAttrValue "name" -< x    value <- getChildren >>> getText -< x    returnA -< LS name value

You'd probably like a little more error-checking (i.e. don't just lazily use atTag like me; actually verify that <root> is root, <elem> is direct descendent, etc.) but this works just fine on your example.

Now, if you need an introduction to Arrows, unfortunately I don't know of any good one. I myself learned it the "thrown into the ocean to learn how to swim" way.

Something that may be helpful to keep in mind is that the proc/-< syntax is simply sugar for the basic arrow operations (arr, >>>, etc.), just like do/<- is simply sugar for the basic monad operations (return, >>=, etc.). The following are equivalent:

getAttrValue "name" &&& (getChildren >>> getText) >>^ uncurry LSproc x -> do    name <- getAttrValue "name" -< x    value <- getChildren >>> getText -< x    returnA -< LS name value

Use one of the XML packages.

The most popular are, in order,

1. haxml
2. hxt
3. xml-light
4. hexpat

FWIW, HXT seems like overkill where a simple TagSoup will do :)