F# 压缩实现

Question

我不知道如何在 F# 中实现 Zip 功能。谁能告诉我我做错了什么？这是我在 fsi.exe:

中输入的内容

> 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"] 是一个包含一个元素的列表，该元素是 4 维元组。这就是为什么您从 zip 中得到意想不到的结果。只需使用 ; 作为元素分隔符即可。

Answer 2

我认为值得指出的是，为了避免较大列表上的堆栈溢出，也可能值得使 zip 函数尾递归。

也许是这样的

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

F# 压缩实现

F# zip implementation

f#

functional-programming

f#-interactive