F# 对于
示例
for序列表达被设计为看起来与其更著名的表亲一样，即命令式for循环。它通过一个序列“循环”，并将每次迭代的主体评估为它正在生成的序列。就像所有与序列相关的东西一样，它不是可变的。
> let oneToTen = seq { for x in 1..10 -> x }
val oneToTen: seq<int> = seq [1; 2; 3; 4; 5; 6; 7; 8; 9; 10]
//或者，等效地：
> let oneToTen = seq { for x in 1..10 do yield x }
val oneToTen: seq<int> = seq [1; 2; 3; 4; 5; 6; 7; 8; 9; 10]
//就像Seq.map：将映射功能应用于序列中的每个项目以构建新序列
> let map mapping seq1 = seq { for x in seq1 do yield mapping x }
> map (fun x -> x * x) [1..10]
val map: ('a -> 'b) -> seq<'a> -> seq<'b>
val it: seq<int> = seq [1; 4; 9; 16; 25; 36; 49; 64; 81; 100]
//从0开始的连续整数的无限序列
> let naturals =
let numbersFrom n = seq { yield n; yield! numbersFrom (n + 1) }
numbersFrom 0
//就像Seq.filter：返回一个序列，该序列仅由输入序列中满足谓词的项目组成
> let filter predicate seq1 = seq { for x in seq1 do if predicate x then yield x }
> let evenNaturals = naturals |> filter (fun x -> x % 2 = 0)
val naturals: seq<int> = seq [1; 2; 3; ...]
val filter: ('a -> bool) -> seq<'a> -> seq<'a>
val evenNaturals: seq<int> = seq [2; 4; 6; ...]
//就像Seq.concat：将一系列序列连接在一起
> let concat seqSeq = seq { for seq in seqSeq do yield! seq }
> concat [[1;2;3];[10;20;30]]
val concat: seq<#seq<'b>> -> seq<'b>
val it: seq<int> = seq [1; 2; 3; 10; 20; 30]