Hello, I'm having some trouble with HXT, the types of some functions in particular. This may well be caused by a lack of understanding for arrow programming -- I'd appreciate any hints. In short, I'm constantly running into what appear to be artificial type restrictions in Control.Arrow.ArrowTree. For example, the signature of "deep" is deep :: (Tree t, ArrowTree a) => a (t b) (t b) -> a (t b) (t b) instead of the more general deep :: (Tree t, ArrowTree a) => a (t b) c -> a (t b) c Say I have an arrow getLink :: (ArrowXml a) => a XmlTree Link that converts an HTML link (<a href="url">text</a>) into some appropriate data type (code below). To collect all links in a document, I'd like to use deep getLink instead of deep (hasName "a") >>> getLink Is this the wrong approach to converting XML into Haskell data types? Cheers Robert module Links where import Text.XML.HXT.Arrow data Link = Link { url, text :: String } deriving Show getLink :: (ArrowXml a) => a XmlTree Link getLink = isElem >>> hasName "a" >>> (getAttrValue0 "href" &&& getAllText) >>> arr (uncurry Link) getAllText :: (ArrowXml a) => a XmlTree String getAllText = listA (deep isText >>> getText) >>> arr concat