random - 在 Elm 中生成随机数所需的最少代码是多少？

Question

我只想看一个随机数。所以这里是 an example straight out of the docs对于随机库。我希望 Random.generate 接受生成器和种子并返回包含随机值和新种子的元组，如:

generate : Generator a -> Seed -> (a, Seed)

-- Main.elm

import Random

seed0 = Random.initialSeed 31415
randomNumber = Random.generate (Random.int 0 10) seed0
main = 
  -- print result of randomNumber here

编译器错误显示两种类型不匹配:

-- TYPE MISMATCH ---------------------------------------------------- -----------

The 2nd argument to function `generate` is causing a mismatch.

5|        Random.generate (Random.int 0 10) seed0
                                        ^^^^^
Function `generate` is expecting the 2nd argument to be:

    Random.Generator a

But it is:

    Random.Seed


The 1st argument to function `generate` is causing a mismatch.

5|        Random.generate (Random.int 0 10) seed0
                       ^^^^^^^^^^^^^^^
Function `generate` is expecting the 1st argument to be:

    a -> b

But it is:

    Random.Generator Int

我在这里错过了什么？

Answer 1

您引用的文档版本是Core 1.0.0，它是旧的。当前版本的核心是 4.0.5。 (docs for Random here)

您要查找的带有签名的函数现在命名为 step:

step : Generator a -> Seed -> (a, Seed)

所以你重构的代码看起来像这样:

import Html exposing (text)
import Random

seed0 = Random.initialSeed 31415
(randomNumber, nextSeed) = Random.step (Random.int 0 10) seed0

main =
  text <| toString randomNumber