[英]how can I make a recursive async function in F#?
我有以下內容:
let getCandlesFrom (exchange: IExchange) (instrument: Instrument) (interval: TimeSpan) (fromTime: DateTime) =
let rec get (c: CandleData array) (f: DateTime) =
let now = DateTime.UtcNow
//info $"requesting {f} - {now}"
let candles = exchange.GetCandles(instrument, interval, f, now)
if candles.IsError then
failwith candles.GetError.Describe
else
//info $"received data {candles.Get.[0].Timestamp} - {candles.Get.[^0].Timestamp}"
let c = Array.append c candles.Get
if c.[^0].Timestamp < now - interval then
get c (c.[^0].Timestamp + interval)
else
c
get [||] fromTime
我想移動這條線:
let candles = exchange.GetCandles(instrument, interval, f, now)
到異步調用:
let! candles = exchange.GetCandlesAsync(instrument, interval, f, now)
但是如果我將整個 function 包裝在一個異步塊中,則遞歸 function 不會編譯,我會收到此錯誤:
DataSource.fs(14, 13): [FS0588] 這個 'let' 后面的塊未完成。 每個代碼塊都是一個表達式,並且必須有一個結果。 'let' 不能是塊中的最后一個代碼元素。 考慮給這個塊一個明確的結果。
我沒有看到您的代碼產生錯誤,但您一定忘記了一些東西(在let
之后) - 這應該有效:
let getCandlesFrom (exchange: IExchange) (instrument: Instrument) (interval: TimeSpan) (fromTime: DateTime) =
let rec get (c: CandleData array) (f: DateTime) =
asnyc {
let now = DateTime.UtcNow
//info $"requesting {f} - {now}"
let! candles = exchange.GetCandlesAsync(instrument, interval, f, now)
if candles.IsError then
return (failwith candles.GetError.Describe)
else
let c = Array.append c candles.Get
if c.[^0].Timestamp < now - interval then
return! get c (c.[^0].Timestamp + interval)
else
return c
}
get [||] fromTime
注意return
和return!
對於遞歸調用 - 你需要那些
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