gistfile1.txt

everythingButM
  :: forall r m
   . (Monad m)
  => (r -> r -> r)
  -> (forall a . Data a => a -> (m r, Bool))
  -> (forall a . Data a => a -> m r)
everythingButM k f x = do
  let (v, stop) = f x
  if stop
    then v
    else Data.gmapQr
      (\e acc -> do
        e' <- e
        a  <- acc
        return (e' `k` a)
      )
      v
      (everythingButM k f)
      x

-- -- | Variation of "everything" with an added stop condition
-- -- Just like 'everything', this is stolen from SYB package.
-- everythingBut :: (r -> r -> r)
--               -> (forall a. Data a => a -> (r, Bool))
--               -> (forall a. Data a => a -> r)
-- everythingBut k f x = let (v, stop) = f x
--                       in if stop
--                            then v
--                            else foldl' k v (gmapQ (everythingBut k f) x)

hie-8.6.4: user error (mzero)