Seq.delay<'T> 函式 (F#)
傳回序列，這個序列是從指定的延遲序列規格所建置。
命名空間/模組路徑：Microsoft.FSharp.Collections.Seq
組件：FSharp.Core (在 FSharp.Core.dll 中)
// Signature:
Seq.delay : (unit -> seq<'T>) -> seq<'T>
// Usage:
Seq.delay generator
參數
傳回值
產生的序列。
備註
每次要求序列的 IEnumerator 時，就會評估輸入函式。
這個函式在已編譯的組件中名為 Delay。如果您是透過 F# 以外的語言，或是透過反映來存取函式，請使用這個名稱。
範例
下列程式碼示範如何使用 Seq.delay，對從通常立即評估之集合中建立的序列延遲進行評估。
// Normally sequences are evaluated lazily. In this case,
// the sequence is created from a list, which is not evaluated
// lazily. Therefore, without Seq.delay, the elements would be
// evaluated at the time of the call to makeSequence.
let makeSequence function1 maxNumber = Seq.delay (fun () ->
let rec loop n acc =
printfn "Evaluating %d." n
match n with
| 0 -> acc
| n -> (function1 n) :: loop (n - 1) acc
loop maxNumber []
|> Seq.ofList)
printfn "Calling makeSequence."
let seqSquares = makeSequence (fun x -> x * x) 4
let seqCubes = makeSequence (fun x -> x * x * x) 4
printfn "Printing sequences."
printfn "Squares:"
seqSquares |> Seq.iter (fun x -> printf "%d " x)
printfn "\nCubes:"
seqCubes |> Seq.iter (fun x -> printf "%d " x)
Output
下列程式碼範例相當於上述範例，但它不會使用 Seq.delay。請注意輸出中的差異。
// Compare the output of this example with that of the previous.
// Notice that Seq.delay delays the
// execution of the loop until the sequence is used.
let makeSequence function1 maxNumber =
let rec loop n acc =
printfn "Evaluating %d." n
match n with
| 0 -> acc
| n -> (function1 n) :: loop (n - 1) acc
loop maxNumber []
|> Seq.ofList
printfn "Calling makeSequence."
let seqSquares = makeSequence (fun x -> x * x) 4
let seqCubes = makeSequence (fun x -> x * x * x) 4
printfn "Printing sequences."
printfn "Squares:"
seqSquares |> Seq.iter (fun x -> printf "%d " x)
printfn "\nCubes:"
seqCubes |> Seq.iter (fun x -> printf "%d " x)
Output
平台
Windows 8 中， Windows 7， Windows Server 2012 上， Windows Server 2008 R2
版本資訊
F# 核心程式庫版本
支援版本:2.0， 4.0，可攜式執行檔 (PE)。