相关疑难解决方法(0)

我在haskell中编写了一个小程序,使用State Monad with Vector计算Tree中所有的Int值的出现次数:

import Data.Vector
import Control.Monad.State
import Control.Monad.Identity

data Tree a = Null | Node (Tree a) a (Tree a) deriving Show
main :: IO ()
main = do 
    print $ runTraverse (Node Null 5 Null)


type MyMon a = StateT (Vector Int) Identity a

runTraverse :: Tree Int -> ((),Vector Int)
runTraverse t =  runIdentity (runStateT (traverse t) (Data.Vector.replicate 7 0))

traverse :: Tree Int -> MyMon ()
traverse Null = return ()
traverse (Node l v …

import           Control.Monad.ST
import           Data.STRef

import qualified Data.Vector.Unboxed         as V
import qualified Data.Vector.Unboxed.Mutable as MV

-- what the heck is that s?
new0 :: (MV.Unbox a, Num a) => ST s (MV.STVector s a)
new0 = do
  v <- MV.new 10
  MV.write v 1 10
  MV.write v 2 10
  return v

new1 :: (MV.Unbox a) => IO (MV.IOVector a)
new1 = MV.new 10

new2 :: (MV.Unbox a, Num a) => IO (MV.STVector RealWorld a)
new2 = do
  v <- MV.new 10 …