.net - 递归序列生成

Question

我正在尝试通过从我的数据源中递归读取数据来生成一系列切片。

let rec read stream startFrom (conn : IEventStoreConnection) = 
    seq {
        let size = 10000
        let slice = conn.ReadStreamEventsForwardAsync(stream, startFrom, size, true).Result

        Console.WriteLine("Events in slice: " + slice.Events.Count().ToString())

        if (slice.IsEndOfStream) then
           yield slice
        else
           yield! read stream (startFrom + 1 * size) conn 
    }

let slices = read "stream-name" 0 conn

Console.WriteLine("TOTAL slices in sequence: " + (Seq.length slices).ToString());

我原以为该序列包含三项，但它似乎只返回一项，即最后一项。

Events in slice: 10000
Events in slice: 10000
Events in slice: 4501
TOTAL slices in sequence: 1

为什么我的递归调用的结果也没有产生？范围界定？

Answer 1

正如 John 已经告诉您的，您还必须 yield 其他切片:

let rec read stream startFrom (conn : IEventStoreConnection) = 
    seq {
        let size = 10000
        let slice = conn.ReadStreamEventsForwardAsync(stream, startFrom, size, true).Result

        Console.WriteLine("Events in slice: " + slice.Events.Count().ToString())

        if (slice.IsEndOfStream) 
        then
           yield slice
        else
           yield slice // here
           yield! read stream (startFrom + 1 * size) conn 
    }

我认为您可以使用内部函数稍微清理一下:

let read (conn : IEventStoreConnection) stream startFrom = 
    let size = 10000
    let rec loop startFrom =
       seq {
           let slice = conn.ReadStreamEventsForwardAsync(stream, startFrom, size, true).Result

           Console.WriteLine("Events in slice: " + slice.Events.Count().ToString())

           if (slice.IsEndOfStream) 
           then
              yield slice
           else
              yield slice // here
              yield! loop (startFrom + 1 * size)
       }
    loop startFrom