如何使用MonadRandom？

Question

有人可以提供"for-dummies"如何使用"MonadRandom"的例子吗？

目前我的代码可以执行诸如传递生成器变量之类的东西,从main函数一直到:

 main = do
     g <- getStdGen
     r <- myFunc g
     putStrLn "Result is : " ++ show r

 --my complicated func
 myFunc g x y z = afunc g x y z
 afunc g x y z = bfunc g x y
 bfunc g x y = cfunc g x
 cfunc g x = ret where
       (ret, _ ) = randomR (0.0, 1.0) g

谢谢

Answer 1

基本上所有额外的g参数都可以删除.然后使用Control.Monad.Random(例如getRandomR)中的函数获取随机数.这是你的例子(我添加了一些args以使其编译):

import Control.Monad.Random

main = do
    g <- getStdGen
    let r = evalRand (myFunc 1 2 3) g :: Double
    -- or use runRand if you want to do more random stuff:
    -- let (r,g') = runRand (myFunc 1 2 3) g :: (Double,StdGen)
    putStrLn $ "Result is : " ++ show r

--my complicated func
myFunc x y z = afunc x y z
afunc x y z = bfunc x y
bfunc x y = cfunc x
cfunc x = do
    ret <- getRandomR (0.0,1.0)
    return ret

Answer 2

你只需在RandTmonad变换器中使用runRandTor 运行一些东西evalRandT,对于纯Randmonad,使用runRand或evalRand:

main = do
  g <- getStdGen
  r = evalRand twoEliteNumbers g
  putStrLn $ "Result is: " ++ show r

twoEliteNumbers :: (RandomGen g) => Rand g (Double, Double)
twoEliteNumbers = do
  -- You can call other functions in the Rand monad
  number1 <- eliteNumber
  number2 <- eliteNumber
  return $ (number1, number2)

eliteNumber :: (RandomGen g) => Rand g Double
eliteNumber = do
  -- When you need random numbers, just call the getRandom* functions
  randomNumber <- getRandomR (0.0, 1.0)
  return $ randomNumber * 1337