How do I do logging in Haskell?

I'm attempting to use HSlogger to get some information about my program. So I add the following line to my function

import Data.Word
import qualified Data.ByteString as B
import qualified Data.ByteString.Lazy as L
import Data.Bits
import Data.Int
import Data.ByteString.Parser

import System.Log.Logger
import System.Log.Handler.Syslog


importFile :: FilePath -> IO (Either String (PESFile ))
importFile n = do
     warningM "MyApp.Component2" "Something Bad is about to happen."
     ...

And that works fine, because the function is inside IO. However when I add a similar line to the following function:

...
parsePES :: Parser PESFile
parsePES = do
        header <- string "#PES"
        warningM "parsing header"
        ...
        return (PESFile ...)

I get a type error:

 Couldn't match expected type `Parser a0'
                with actual type `String -> IO ()'
    In the return type of a call of `warningM'
    In a stmt of a 'do' expression: warningM "parsing header"
    In the expression:
      do { header <- string "#PES";
           warningM "parsing header";
        ...

And I totally understand why - parsePES is in the Parser monad, not the IO monad. What I don't understand is what to do about it. Do I need a monad transformer so I can stack the Parser monad and the IO monad together? How do I go about that?