f# - 如何遍历联合案例列表并访问每个案例的数据？

Question

如何遍历联合案例列表并访问每个案例的数据？

我有这一行:

root.Neighbors |> Seq.filter(fun x -> print x)

但是，Neighbors 是一个列表:

Neighbors=[ One   { State=Survives; Neighbors=[] }
            Two   { State=Survives; Neighbors=[] }
            Three { State=Survives; Neighbors=[] }
            Four  { State=Survives; Neighbors=[] }
            Six   { State=Survives; Neighbors=[] }
            Seven { State=Survives; Neighbors=[] }
            Eight { State=Survives; Neighbors=[] }
            Nine  { State=Survives; Neighbors=[] } ]

我需要访问邻居列表中每个邻居的状态。

但是，我收到以下错误:

The type 'Neighbor' does not match the type 'Cell' Type mismatch. Expecting a Neighbor -> unit but given a Cell -> unit

注意:我真的需要进行模式匹配才能访问所有邻居吗？

代码:

module GameOfLife

type Neighbor = | One   of Cell
                | Two   of Cell
                | Three of Cell
                | Four  of Cell

                | Six   of Cell
                | Seven of Cell
                | Eight of Cell
                | Nine  of Cell

and CauseOfDeath = | Underpopulated // Fewer than 2 live neighbors
                   | Overpopulated  // More than 3 live neighbors

and State = | Dies of CauseOfDeath  
            | Survives    // 2 or 3 live neighbors
            | Resurected  // Is dead and has 3 live neighbors

and Neighbors = Neighbor List

and Cell = { State:State; Neighbors:Neighbors }

let letThereBeLife() = 
    { State=Survives; Neighbors=[ One   { State=Survives; Neighbors=[] }
                                  Two   { State=Survives; Neighbors=[] }
                                  Three { State=Survives; Neighbors=[] }
                                  Four  { State=Survives; Neighbors=[] }
                                  Six   { State=Survives; Neighbors=[] }
                                  Seven { State=Survives; Neighbors=[] }
                                  Eight { State=Survives; Neighbors=[] }
                                  Nine  { State=Survives; Neighbors=[] } ] }


let print (cell:Cell) =
    printf "This cell %A\n%A" cell.State cell.Neighbors

let tick root =
    root.Neighbors |> Seq.iter(print)

Answer 1

当您有一个复杂的区分联合，其中的案例在案例之间共享一些共同的状态，并且您想将它隐藏在一个更简单的界面后面时，一种技术是让一个成员隐藏模式匹配样板。

type Neighbor =
    | One of Cell
    ...
    | Nine of Cell 
    static member Cell (n: Neighbor) = 
        match n with
        | One cell
        ...
        | Nine cell -> cell

 root.Neighbors |> Seq.iter (Neighbor.Cell >> print)

然而，正如其他人在评论中提到的那样，您真的应该重新考虑您的设计。这种巨大的 Neighbor 类型感觉就像你歧视了一个错误的维度。