Simple Haskell Monad - 随机数 [英] Simple Haskell Monad - Random Number
问题描述
我试图扩展这篇文章中的代码(接受的答案),以便让我能够根据函数randomGen调用randomGen2来获得一个随机数,该函数将种子作为参数。但每次我调用randomGen2,尽管返回一个Int,我得到一个关于不能打印随机的错误(当我试图打印Int时)。
< interactive>:3:1:
(Show(Random Int))
使用`print'
可能的修正:为(Show(Random Int))添加一个实例声明
在一个交互式GHCi命令中:print it
$ b以下是代码:
import Control.Monad.State
type Seed = Int
randomGen :: Seed - > (种子,种子)
randomGen种子=(种子,种子+ 1)
类型随机a =状态种子a
randomGen2 :: Random Int
randomGen2 = do
seed< - get
let(x,seed')= randomGen seed
放入种子'
return x
有什么想法?
更新 - 预期行为 $ b我希望能够从翻译人员那里做些什么(例如GHCI) -
> getRandomInit 1
> - 其他一些东西,例如2 + 3
> getRandom
即我可以使用种子设置我的getRandom函数,然后使用
put
存储种子,然后此函数返回并退出。然后我做了一些其他的事情,然后再次调用getRandom,并从Monad中取回它的种子。 解决方案
randomGen2
返回一个 Random Int
,它是一个 State Seed Int
所以你需要使用 runState
来获得一个结果,通过提供一个种子值例如
runState randomGen2 1
如果您想继续重复使用 randomGen2
您可以创建一个函数,如:
genRandoms :: Seed - > [int]
genRandoms s = let(v,s')= runState randomGen2 s in v:genRandoms s'
或者您可以使用序列
:
genRandoms ::种子 - > [Int]
genRandoms s = fst $ runState(sequence(repeat randomGen2))s
I'm trying to extend the code in this post (accepted answer) to allow me to be able to call randomGen2 to get a random number, based on the function randomGen which takes a seed as an argument. But everytime I call randomGen2, despite returning an Int, I get an error about not been able to print Random (when infact I am only trying to print Int).
<interactive>:3:1:
No instance for (Show (Random Int))
arising from a use of `print'
Possible fix: add an instance declaration for (Show (Random Int))
In a stmt of an interactive GHCi command: print it
Here's the code:
import Control.Monad.State
type Seed = Int
randomGen :: Seed -> (Int, Seed)
randomGen seed = (seed,seed+1)
type Random a = State Seed a
randomGen2 :: Random Int
randomGen2 = do
seed <- get
let (x,seed') = randomGen seed
put seed'
return x
any ideas?
Update - expected behaviour I'm hoping to be able to do something this from an interpreter (e.g. GHCI) -
> getRandomInit 1
> -- some other stuff, e.g. 2 + 3
> getRandom
i.e. I can set up my getRandom function with a seed, which then stores the seed using put
, then this function returns and exits. I then do some other stuff, then call getRandom again, and the seed is retrieved from the Monad where it was stored.
randomGen2
returns a Random Int
which is a State Seed Int
so you'll need to use runState
to get a result by providing a seed value e.g.
runState randomGen2 1
If you want to keep repeating the application of randomGen2
you can create a function like:
genRandoms :: Seed -> [Int]
genRandoms s = let (v, s') = runState randomGen2 s in v : genRandoms s'
or you could use sequence
:
genRandoms :: Seed -> [Int]
genRandoms s = fst $ runState (sequence (repeat randomGen2)) s
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