我如何在状态monad中使用Debug.Trace.trace？

type State s a = s -> (a, s)

import Control.Monad.State

type Stack = [Int]

push :: Int -> State Stack ()
push x = do
    xs <- get
    put (x:xs)

pop :: State Stack (Maybe Int)
pop = do
    xs <- get
    case xs of
        [] -> return Nothing
        (x:xs) -> do
            put xs
            return (Just x)

import Debug.Trace

add :: Int -> Int -> Int
add x y = trace ("Adding " ++ show x ++ " and " ++ show y) $ x + y

import Control.Monad.State
import Debug.Trace

type Stack = [Int]

push :: Int -> State Stack ()
push x = do
    xs <- get
    trace ("Pushing " ++ show x) $ return ()
    put (x:xs)

pop :: State Stack (Maybe Int)
pop = do
    xs <- get
    case xs of
        [] -> return Nothing
        (x:xs) -> do
            trace ("Popping " ++ show x) $ return ()
            put xs
            return (Just x)