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F#从列表中选择0或1的区分联合

discriminated-union filter f# list

1

Dylan · 技术社区 · 15 年前

type thing = { One:int; Two:int; Three:int}

type data = 
    | Alpha of int
    | Bravo of thing
    | Charlie of string
    | Delta of Object

//generate some data
let listData = [
                Alpha(1);
                Alpha(2);
                Bravo( { One = 1; Two = 2; Three = 3 } );
                Charlie("hello");
                Delta("hello again")]

//find the 0 or 1 instances of bravo and return the data as a thing
let result =    listData 
                |> List.map( function | Bravo b -> Some(b) | _ -> None)
                |> List.filter( fun op -> op.IsSome)
                |> (function | [] -> None | h::t -> Some(h.Value))

谢谢

2 回复 | 直到 15 年前

1

2

kvb 15 年前

怎么样

let result =
  listData
  |> List.tryPick (function | Bravo b -> Some b | _ -> None)

2

0

dahlbyk 15 年前

let result = listData
             |> List.tryFind (function | Bravo b -> true | _ -> false)