liftwoes.hs

{-# LANGUAGE TemplateHaskell #-}
import           Data.Data
import qualified Data.Set                   as HS
import           Data.Time
import           Language.Haskell.TH.Syntax

foo :: (Data a) => a -> ()
foo _ = ()


table = $(do r <- runIO (HS.fromList . lines  <$> readFile "/usr/share/dict/words")
             [|r|] )

main = do
  r <- HS.fromList . lines  <$> readFile "/usr/share/dict/words"
  print (foo r)
  print $ HS.member "foo" table

class Lift t where
  -- | Turn a value into a Template Haskell expression, suitable for use in
  -- a splice.
  lift :: t -> Q Exp
  default lift :: Data t => t -> Q Exp
  lift = liftData

Am a bit confused by this - do I need to explicitly derive Lift for Data.Set? if so, what use is the defaulting in the Lift class?