list - F# 列出文件夹和文件
问题描述
我必须编写一个名为“find”的函数,我可以在其中给出一个名称作为输入。该函数必须搜索具有给定名称的文件或文件夹,并且必须在列表中返回它们。
在这里,您有一个应该是什么样子的示例:
find "Hallo" hallo = []
find "Hallo.txt" hallo = [["Hallo.txt"]]
find "Hallo.txt" dokumente = [["Dokumente"; "Hallo.txt"]]
find "Hallo.txt" (Folder ("Test", [hallo; dokumente ])) =
[["Test"; "Hallo.txt"]; ["Test"; "Dokumente"; "Hallo.txt"]]
这就是我到目前为止所尝试的:
type Node =
| File of string * Nat
| Folder of string * (Node list)
let rec find (name: string) (root: Node): string list list =
match root with
| File (N,G) ->if N=name then [[N]] else find(name)(root)
| Folder(N,G) ->if N=name then [[N]] else find(name)(root)
解决方案
let find name root =
let rec loop name node acc =
[ match node with
| File (n) -> if n = name then yield List.rev (n::acc)
| Folder (n, l) -> for x in l do yield! loop name x (n::acc) ]
loop name root []