F＃zip實現

Question

我無法弄清楚如何在F＃中實現Zip函數。誰能告訴我我做錯了什麼？以下是我已經輸入到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

在您的例子["a","b","c","d"]是包含一個元素，這是4維的元組的列表。這就是爲什麼你從zip獲得意想不到的結果。 改爲使用;作爲元素分隔符。

Answer 2

我認爲值得指出的是，爲了避免在較大的列表上出現堆棧溢出，可能值得使用zip函數進行尾遞歸。

像這樣的事情也許

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