Template Haskell はHaskellの言語仕様には無くGHCの独自拡張なのでGHCのバージョンが変わる毎に仕様も変わる可能性があるので注意

{-# LANGUAGE QuasiQuotes #-}
import Language.Haskell.TH.Quote

readCSV xs = let (ys, zs) = break (==',') xs
             in if null zs then [ys]
                           else ys : readCSV (tail zs)

csv :: QuasiQuoter
csv = QuasiQuoter
      { quoteExp  = exp
      , quotePat  = undefined
      , quoteType = undefined
      , quoteDec  = undefined
      }
      where
      exp = dataToExpQ (const Nothing) . readCSV

>>> [csv|1,2,3|]
["1","2","3"]