f# - F# 是否有异步验证库？

Question

我在我的代码中经常使用 asyncResult 但它会在第一个错误时退出:

asyncResult {

    let! a = allGood()
    let! b = thisReturnsError()
    let! c = neverExecuted()
}

但有时我想执行所有功能并总结错误:

validation {
    let! a = doSomething()
    and! b = doSomethingElse()
    and! c = andAnotherThing()
}

然后我要么得到一个 Ok，要么得到一个带有错误列表的 Error。

这很好，但我希望能够同时做到这两点!

asyncValidation {
    let! a = doSomethingAsync()
    and! b = doSomethingElseAsync()
    and! c = andAnotherThingAsync()
}

有库在做这个吗？

Answer 1

与 F#+您可以使用 Compose 组合应用程序:

#r @"nuget: FSharpPlus"

open FSharpPlus
open FSharpPlus.Data

// Generic applicative CE. At the moment not included in the library.
type ApplicativeBuilder<'a>() =
    inherit MonadFxStrictBuilder<'a>()
    member inline _.BindReturn(x, f) = map f x
let applicative<'t> = ApplicativeBuilder<'t> ()


let allGoodAsync () : Async<Validation<string, int>> = async { printfn "first success"; return Success 1 }
let thisResturnsErrorAsync () : Async<Validation<string, int>> = async { return Failure "thisReturnsError" }
let neverExecutedAsync () : Async<Validation<string, int>> = async { printfn "actually executed"; return Success 3 }

let x: Async<Validation<string, _>> =
    applicative {
        let! (a: int) = allGoodAsync () |> Compose
        and! (b: int) = thisResturnsErrorAsync () |> Compose
        and! (c: int) = neverExecutedAsync () |> Compose
        return a + b + c
        }
    |> Compose.run
let y = Async.RunSynchronously x

结果

> 
first success
actually executed
val y: Validation<string,int> = Failure "thisReturnsError"

更新

重新审视这个答案，这可以进一步简化如下:

type ApplicativeBuilder2<'a>() =
    inherit Builder<'a>()
    member inline _.BindReturn(x, f) = map f x
    member inline _.Source x = Compose x
    member inline _.Run x = Compose.run x
let applicative2<'t> = ApplicativeBuilder2<'t> ()

所以你不需要搞乱 Compose :

let x: Async<Validation<string, _>> =
    applicative2 {
        let! (a: int) = allGoodAsync ()
        and! (b: int) = thisResturnsErrorAsync ()
        and! (c: int) = neverExecutedAsync ()
        return a + b + c
        }

并且由于评论中提到的 F# 类型推断错误仍未修复，我现在可以说 applicative 和 applicative2 肯定会包含在下一版本的F#+。