[Haskell-cafe] Beginners arrow question

I'm using arrows for the first time, with HXT. I think I'm getting the hang of it, but one problem has me stumped. I have a function "lookupFormatter" which takes a string and returns an arrow, and I want to use that arrow. Something like this: myProblem :: (ArrowXml a) -> a XmlTree String myProblem = proc xml do name <- getAttrValue "name" -< xml fmt <- arr lookupFormatter -< name fmt -< xml But I can't figure out how to do it. I get "fmt: not in scope". Can anyone help? Thanks, Paul.