State monad

gistfile1.hs

{-# LANGUAGE NoMonomorphismRestriction #-}

import Control.Monad.State
import Control.Monad.Identity

test1 = do        -- when apply on init state 0
  a <- get        -- a = (0,0)
  modify (+1)     -- (0,1)
  b <- get        -- b = (1,1)
  return (a,b)    -- why result is ((0,1),1)

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runState test1 0
((0,1),1)   为什么啊？