f# – 流水线与API设计的部分应用程序

在设计API时,我可以遵循这种趋势,就像在这个简单的状态机示例中一样：

type Transition =
    { CurrentState : string; TriggeringEvent : string; NewState : string }

let getNewState currentState triggeringEvent transitions =
    let isMatch t =
        t.CurrentState = currentState
        && t.TriggeringEvent = triggeringEvent
    match transitions |> Seq.tryFind isMatch with
    | Some transition -> Some(transition.NewState)
    | None -> None

let myTransitions =
    [ { CurrentState = "A"; TriggeringEvent = "one"; NewState = "B" };
      { CurrentState = "B"; TriggeringEvent = "two"; NewState = "A" } ]

let result = myTransitions |> getNewState "A" "one"

printfn "%A" result

这里getNewState有签名：

(string -> string -> seq<Transition> -> string option)

它支持流水线操作：

myTransitions |> getNewState "A" "one"

但在某些情况下,序列是不变的,而其他参数则不同.在状态机示例中,对于给定的状态机,转换表(转换)将是固定的.将使用不同的状态和事件多次调用getNewState.如果序列是第一个参数,则调用者可以使用部分应用程序：

let getNewState transitions currentState triggeringEvent =
    // body same as before

let stateMachine = getNewState myTransitions

let result1 = stateMachine "A" "one"
let result2 = stateMachine "B" "two"

printfn "%A" result1
printfn "%A" result2

现在getNewState有签名：

(seq<Transition> -> string -> string -> string option)

和stateMachine签名：

(string -> string -> string option)

如何在调用者选项中设计API以支持流水线操作和部分应用程序？