F＃zip實現

Question

我無法弄清楚如何在F＃中實現Zip功能。 誰能告訴我我做錯了什么？ 這是我輸入fsi.exe ：

> let rec zip xs ys =
-  match xs with
-   | [] -> []
-   | head :: tail -> (match ys with
-                       | [] -> []
-                       | headY :: tailY -> (head, headY) :: zip tail tailY);;

val zip : xs:'a list -> ys:'b list -> ('a * 'b) list

> zip [1;2;3;4] ["a","b","c","d"];;
val it : (int * (string * string * string * string)) list =
  [(1, ("a", "b", "c", "d"))]

Answer 1

在您的示例中["a","b","c","d"]是包含一個元素的列表，該元素是4維元組。 這就是為什么你從zip獲得意想不到的結果。 只是用; 作為元素分隔符而不是。

Answer 2

我認為值得指出的是，為了避免大型列表上的堆棧溢出，可能還需要使zip函數尾遞歸。

或許這樣的事情

let zip3 xs ys = 
  let rec loop r xs ys =
    match xs,ys with 
    | [],[]         -> r
    | xh::xt,yh::yt -> loop ((xh,yh)::r) xt yt
    | _ -> failwith "xs & ys has different length"
  loop [] xs ys |> List.rev