Purescript 卤素，副作用（随机数）

Question

在 PureScript Halogen 项目中，我想将状态设置为随机数，但如何提取值？正常

r <- randomInt 1 10

在 eval 函数中时不编译。

module Main where

import Prelude
import Control.Monad.Eff (Eff)
import Control.Monad.Eff.Random (randomInt, RANDOM)
import Halogen as H
import Halogen.HTML.Events.Indexed as HE
import Halogen.HTML.Indexed as HH
import Halogen.Util (runHalogenAff, awaitBody)

type State = { n::Int }

initialState :: State
initialState = { n: 3}

data Query a = NewRandom a

ui :: forall e. H.Component { n :: Int } Query e
ui =
    H.component { render, eval }
    where
    render :: State -> H.ComponentHTML Query
    render state =
        HH.button
            [ HE.onClick $ HE.input_ NewRandom ]
            [ HH.text $ show state.n ]


    eval :: Query ~> H.ComponentDSL State Query e
    eval (NewRandom next) = do
        H.modify (\state -> state { n=12 } )

        --I'd like to set n to a random number
        --but I don't know how.
        --let r = randomInt 1 10
        --H.modify (\state -> state { n=r } )
        pure next

main :: Eff (H.HalogenEffects ()) Unit
main =
    runHalogenAff do
    body <- awaitBody
    H.runUI ui initialState body

Answer 1

你需要在你的 ComponentDSL 中使用合适的 monad（你目前有 e 类型的 var）才能实现，然后你可以使用 H.fromEff 提升randomInt:

module Main where

import Prelude
import Control.Monad.Aff (Aff)
import Control.Monad.Eff (Eff)
import Control.Monad.Eff.Random (randomInt, RANDOM)
import Halogen as H
import Halogen.HTML.Events.Indexed as HE
import Halogen.HTML.Indexed as HH
import Halogen.Util (runHalogenAff, awaitBody)

type State = { n::Int }

initialState :: State
initialState = { n: 3}

data Query a = NewRandom a

ui :: forall eff. H.Component { n :: Int } Query (Aff (random :: RANDOM | eff))
ui =
    H.component { render, eval }
    where
    render :: State -> H.ComponentHTML Query
    render state =
        HH.button
            [ HE.onClick $ HE.input_ NewRandom ]
            [ HH.text $ show state.n ]


    eval :: Query ~> H.ComponentDSL State Query (Aff (random :: RANDOM | eff))
    eval (NewRandom next) = do
        r <- H.fromEff $ randomInt 1 10
        H.modify (\state -> state { n=r } )
        pure next

main :: forall eff. Eff (H.HalogenEffects (random :: RANDOM | eff)) Unit
main =
    runHalogenAff do
    body <- awaitBody
    H.runUI ui initialState body

(旁白：如果你正在做有效的事情，即使你只需要 Eff，最简单的方法是使用 Aff 作为 ComponentDSL monad，就像你使用 runUI 它期望它是 Aff - 可以在 Halogen.Component 模块中使用 interpret 来更改 monad，但是因为你只是使用 interpret liftAff 反正你也可以直接上Aff.)

查看 "Non-state effects" section of the guide, or the AJAX example 以了解有关 eval 中运行效果的更多详细信息。

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