non-working example of declareFields

DeclareFields.hs

{-# LANGUAGE TemplateHaskell #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE FunctionalDependencies #-}
{-# LANGUAGE FlexibleInstances #-}

module Main where

import Control.Lens

declareFields [d|
    data Foo = Foo {fooXy :: String
                   ,fooYz :: String } deriving Show
              |]
{-makeFields ''Foo-}
main = do
    let foo = Foo "hi" "there"
    putStrLn $ foo^.xy