On 05/04/2008, Paul Johnson
myProblem :: (ArrowXml a) -> a XmlTree String myProblem = proc xml do name <- getAttrValue "name" -< xml fmt <- arr lookupFormatter -< name fmt -< xml
GHC has a special syntax for using ArrowApply (which HXT is an instance of). Whenever the expression to the left of -< needs to involve a local variable, you can replace -< with -<< and it should work. To understand better what it means, you can read http://www.haskell.org/ghc/docs/latest/html/users_guide/arrow-notation.html -- it's basically just a shorthand for using 'app'.
myProblem :: (ArrowXml a) -> a XmlTree String myProblem = proc xml do name <- getAttrValue "name" -< xml fmt <- arr lookupFormatter -< name fmt -<< xml
Try that and see how it goes. - Cale