我可以在F#中同时使用不同的工作流程吗? [英] Can I use different workflows simultaneously in F#?

问题描述

我需要传递我的状态，同时能够与可能的工作流链接功能.有两种方法可以共享相同的上下文吗?如果没有，怎么办?

更新:

好吧，我有一个状态，表示要在数据库中创建的实体的可用ID的一部分.因此，一旦获取了ID，就必须将状态转换为具有下一个可用ID的较新状态，然后将其丢弃，以使任何人都无法再次使用它.我不想为了惯用而改变状态. State monad隐藏了转换并传递了状态，因此看起来就像是要走的路.一旦状态工作流就位，我将无法使用Maybe工作流，这是我在各处使用的东西.

解决方案

如上一个答案所述，在F#(Haskell中的Monads)中组合工作流的一种方法是使用一种称为Monad Transformers的技术.

在F#中，这确实很棘手，这里是一个处理该技术的项目. >

可以使用该库通过自动组合State和Maybe(选项)来编写上一个答案的示例:

#r @"c:\packages\FSharpPlus-1.0.0\lib\net45\FSharpPlus.dll"

open FSharpPlus
open FSharpPlus.Data

// Stateful computation
let computation =
    monad {
        let! x = get
        let! y = OptionT (result (Some 10))
        do! put (x + y)
        let! x = get
        return x
    }

printfn "Result: %A" (State.eval (OptionT.run computation) 1)

这是另一种选择，而不是创建自定义工作流，而是使用将自动推断出的通用工作流(a-la Haskell).

I need my state to be passed along while being able to chain functions with the maybe workflow. Is there a way for 2 workflows to share the same context? If no, what is the way of doing it?

UPDATE:

Well, I have a state that represents a segment of available ID's for the entities that I am going to create in the database. So once an ID is acquired the state has to be transformed to a newer state with the next available ID and thrown away so that nobody can use it again. I don't want to mutate the state for the sake of being idiomatic. The State monad looks like a way to go as it hides the transformation and passes the state along. Once the state workflow is in place I cannot use the Maybe workflow which is something I use everywhere.

解决方案

As stated in the previous answer, one way to combine workflows in F# (Monads in Haskell) is by using a technique called Monad Transformers.

In F# this is really tricky, here is a project that deals with that technique.

It's possible to write the example of the previous answer by automatically combining State and Maybe (option), using that library:

#r @"c:\packages\FSharpPlus-1.0.0\lib\net45\FSharpPlus.dll"

open FSharpPlus
open FSharpPlus.Data

// Stateful computation
let computation =
    monad {
        let! x = get
        let! y = OptionT (result (Some 10))
        do! put (x + y)
        let! x = get
        return x
    }

printfn "Result: %A" (State.eval (OptionT.run computation) 1)

So this is the other alternative, instead of creating your custom workflow, use a generic workflow that will be automatically inferred (a-la Haskell).

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