小编use*_*080的帖子

我想使用库System.Random.MWC生成范围(0,30)中的随机整数.我可以使用库System.Random来做到这一点:

import System.Environment

import System.IO.Unsafe                                        

import System.Random

p :: Integer -> Integer

p n = unsafePerformIO (getStdRandom (randomR (0 , n)))

main :: IO()

main = do
        print $! (p 30)}

但我对System.Random.MWC感到困惑.

我想一个转换IO Int到Int从System.Random.MWC使用unsafePerformIO.它在ghci中有效:

Prelude System.Random.MWC System.IO.Unsafe> let p = unsafePerformIO(uniformR (0, 30) gen :: IO Int)

Prelude System.Random.MWC System.IO.Unsafe> p

11

Prelude System.Random.MWC System.IO.Unsafe> :t p

p :: Int

但是在GHC

import System.Random.MWC
import System.IO.Unsafe  

main :: IO()
main = do
        gen <-createSystemRandom
        print $! s 30 gen

s :: Int-> GenIO -> Int
s !k g = unsafePerformIO(uniformR (0, k - 1) g)

它返回

ghc: panic! (the 'impossible' happened)
(GHC version 7.6.3 for …