[英]how can I make a recursive async function in F#?
我有以下内容:
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
我想移动这条线:
let candles = exchange.GetCandles(instrument, interval, f, now)
到异步调用:
let! candles = exchange.GetCandlesAsync(instrument, interval, f, now)
但是如果我将整个 function 包装在一个异步块中,则递归 function 不会编译,我会收到此错误:
DataSource.fs(14, 13): [FS0588] 这个 'let' 后面的块未完成。 每个代码块都是一个表达式,并且必须有一个结果。 'let' 不能是块中的最后一个代码元素。 考虑给这个块一个明确的结果。
我没有看到您的代码产生错误,但您一定忘记了一些东西(在let
之后) - 这应该有效:
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!
对于递归调用 - 你需要那些
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