f# - 如何在 F# 模式匹配中 "compress"相似分支

Question

我手头有以下代码:

    match intersection with
    | None ->
        printfn "Please provide an empty intersection for ring placement"
        gameState
    | Some x ->
        match x.Status with
        | Empty ->
            let piece = { Color = gameState.Active.Color; Type = Ring }
            putPieceOnIntersection gameState.Board pos piece

            printfn "%s ring placed at %A" (colorStr gameState.Active.Color) pos

            // Decide if we ended this phase
            let updatedPhase = if ringsPlaced = 10 then Main else Start(ringsPlaced + 1)
            let newActivePlayer = gameState.Players |> Array.find (fun p -> p.Color = invertColor gameState.Active.Color)
            let updatedGameState = { gameState with Active = newActivePlayer; CurrentPhase = updatedPhase }

            updatedGameState
        | _ ->
            printfn "Please provide an empty intersection for ring placement"
            gameState

如您所见，如果变量交集是 None 或其状态不同于空，我应该执行完全相同的打印一些文本并返回的分支。但是我不知道如何在 F# 中执行这种条件表达式，以便我可以共享相同的分支。在命令式编程中，我很容易做到这一点，但在 F# 中我该怎么做？

谢谢

Answer 1

如果 Status 是记录字段，那么您可以执行以下操作:

match intersection with
| Some { Status = Empty } ->
    // Code for empty...
| _ ->
    printfn "Please provide an empty intersection for ring placement"
    gameState

否则，您可以使用 guard :

match intersection with
| Some x when x.Status = Empty ->
    // Code for empty...
| _ ->
    printfn "Please provide an empty intersection for ring placement"
    gameState