F#：声明函数并在列表中查找元素

Question

我是 F# 的新手，遇到问题需要一些帮助。我在查找列表中的元素时遇到问题： "Declare a function findRoute: Lid*LuggageCatalogue -> Route, that finds the route for a given luggage identification in a luggage catalogue"

我列出了不同的类型并给出了类型元素。

    type Lid = string 
    type Flight = string
    type Airport = string
    type Route = (Flight*Airport) list
    let route = [("DL 189","ATL"); ("DL 124","BRU"); ("SN 733","CPH"); ("SK 208","ATL"); ("DL 124","BRU"); ("SK 122","JFK")]

    type LuggageCatalogue = (Lid*Route) list
    let lc = [("DL 016-914", [("DL 189","ATL"); ("DL 124","BRU"); ("SN 733","CPH")]); 
    ("SK 222-142", [("SK 208","ATL"); ("DL 124","BRU"); ("SK 122","JFK")])]


    let findRoute fr = function
    match fr with
    | [] -> printf "No match"
    |

我卡住的地方是我找不到使用该函数在 LuggageCatalogue 列表

中查找元素的正确方法

Answer 1

也许您可以先过滤行李目录以更好地了解发生了什么，例如

let filterlist lid = List.filter (fun (luggageid, _) -> luggageid = lid)

然后在目录中查找特定项目就像

filterlist "SK 222-142" lc

或者更好的是，尝试自己创建函数的第一部分。尽管这只是第一步，也许可以尝试想象一下行李 id 的递归搜索功能的外观，

let findfirst lid =
  let rec checktail lctail =
    match lctail with
    | [] -> invalidArg "lid" "luggageid not present in catalogue"
    | (id, r)::tail -> if id = lid then r else checktail tail
  checktail lc

F#：声明函数并在列表中查找元素

F#: Declare function and find element in list

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