How to fix this issue in a simple HXT function?

Question

I've started the friendly tutorial tutorial on HXT to parse XML file with haskell.

In the first page of the tutorial we try to retrieve guest from a xml file. And there is the following function for that.

data Guest = Guest {firstName, lastName :: String}
    deriving (Show, Eq)

getGuest = deep (isElem >>> hasName "guest") >>>                                
 proc x -> do                                                                   
    fname <- getText <<< getChildren <<< deep (hasName "fname") -< x            
    lname <- getText <<< getChildren <<< deep (hasName "lname") -< x            
    returnA -< Guest {firstName = fname, lastName = lname} 

but when I tried to load the file in the interpreter ghci. I still get this error :

Prelude> :l hxt_tuto.hs
hxt_tuto.hs:15:37: parse error on input `->'
Failed, modules loaded: none.

pointing the fact that operator -> in the expression proc x -> do has a parse error, I've try many modification without help. like writing all this in a single line

getGuest2 = deep (isElem >>> hasName "guest") >>> proc x -> do { fname <- getText <<< getChildren <<< deep (hasName "fname") -< x; lname <- getText <<< getChildren <<< deep (hasName "lname") -< x; returnA -< Guest {firstName = fname, lastName = lname }}

Can anybody Help me understand what I've missed ?

thanks for any reply!

Answer 1

Did you remember to put

{-# LANGUAGE Arrows, NoMonomorphismRestriction #-}
import Text.XML.HXT.Core

at the top of your file?