asynchronous - 异步不可知的高阶函数

Question

假设我们有一个提供高阶函数的库 applyTest .

这可以与异步函数一起使用吗asyncFunction同时保留异步代码的好处？

是否可以将库设计为更好地支持异步应用程序，而无需专门提供异步版本？

let applyTest f =
    f 2 > 0

let syncFunction x =
    x - 1

let asyncFunction x =
    x - 2 |> async.Return

async {
    let a = applyTest syncFunction
    let b = applyTest (asyncFunction >> Async.RunSynchronously)
    printfn "a = %b, b = %b" a b
}
|> Async.RunSynchronously

Answer 1

如果您不想丢失强类型检查或像示例中那样同步运行异步计算，则需要提供单独的异步版本。这两种情况都应该尽量避免。

如果您想避免重复实际测试部分( f 2 > 0 )，您可以将其拆分为一个传递参数 2 的函数。到函数和检查值是否大于零的函数:

// LIBRARY CODE

let checkValue x = x > 0

// This function is generic so it can return a value or an async value
// (int -> 'a) -> 'a
let runTestFunction f = f 2

// (int -> int) -> bool
let applyTest f = f |> runTestFunction |> checkValue

// (int -> Async<int>) -> Async<bool>
let applyTestAsync f = async {
    let! value = runTestFunction f // use let! to await the value
    return checkValue value }

// USAGE

let syncFunction x = x - 1
let asyncFunction x = x - 2 |> async.Return

async {
    let a = applyTest syncFunction
    let! b = applyTestAsync asyncFunction // use let! to await the test result
    printfn "a = %b, b = %b" a b
}

另一种选择是使用重载方法。这建立在上面定义的函数之上:

type Test =
    static member Apply f = applyTest f
    static member Apply f = applyTestAsync f

// USAGE

async {
    let a = Test.Apply syncFunction
    let! b = Test.Apply asyncFunction // We still need to consume this differently with a let!
    printfn "a = %b, b = %b" a b
}