f# - FSharp - 基于数组的匹配和返回记录的意外行为

Question

我刚刚真正进入 FSharp 并且我已经为此苦苦挣扎了很长一段时间，因为我不明白为什么我没有在比赛声明中得到预期的结果。

根据消息编号，我需要将数组(拆分)中的某些值与我想要返回的记录上的字段相匹配。

let UNMATCHED = "UNMATCHED"
let T0200 = "T0200" ;; let R0200 = "R0200"

let matchTypes = [| { MessageType = T0200; Regex = REGEX_T0200 }
                ; { MessageType = R0200; Regex = REGEX_R0200 }
...

let messageInfo (matchType:MatchType, line:string) =
    let matching = Regex.Match(line, REGEX_DATA)
    let splits = matching.Value.Replace("[","").Replace("]","").Split('|')
    let showSplit (x:string[]) = "[" + String.Join(";",x) + "]"
    let info =
        Console.WriteLine("matching against: " + matchType.MessageType)
        match matchType.MessageType with
            | T0200 -> 
                { MessageType = T0200; CustomerID = splits.[1]; CustomerName = "";
                        ItemID = splits.[2]; ItemDescription = "" }
            | R0200 ->
                { MessageType = R0200; CustomerID = splits.[1]; CustomerName = splits.[2];
                        ItemID = splits.[5]; ItemDescription = splits.[6] }
            ...
            | UNMATCHED ->  { MessageType = UNMATCHED; CustomerID = ""; CustomerName = "";
                        ItemID = ""; ItemDescription = "" }
            | _ ->  { MessageType = UNMATCHED; CustomerID = ""; CustomerName = "";
                        ItemID = ""; ItemDescription = "" }
    Console.WriteLine("messageInfo: {0}", (matchType, showSplit splits, info))
    info

但是，这似乎不起作用，从下面的输出中，我得到了 T0200 的预期结果，但是对于 R0200，字段的映射与数组中的字段不匹配 - 即。它似乎使用与 T0200 语句相同的数组索引。我对所有其他后续消息都有完全相同的问题。

matching against: T0200
messageInfo: ({MessageType = "T0200";
 Regex = "\sT0200\[([\w\s]*\|)*[\w\s]*\]";}, [3;000008757051;1401], {MessageType = "T0200";
 CustomerID = "000008757051";
 CustomerName = "";
 ItemID = "1401";
 ItemDescription = "";})
matching against: R0200
messageInfo: ({MessageType = "R0200";
 Regex = "\sR0200\[([\w\s]*\|)*[\w\s]*\]";}, [3;000008757051;Ricky Bobby;413792;0;1401;SNACKER;909;0], {MessageType = "R0200";
 CustomerID = "000008757051";
 CustomerName = "";
 ItemID = "Ricky Bobby";
 ItemDescription = "";})

我猜我的 match 语句的语法有问题 - 我做错了什么？

我在 ubuntu 上运行 dotnet core 2.0.2

谢谢

Answer 1

MessageType是一个字符串和 T0200只是一个命名的字符串值。当您尝试在 T0200 上匹配时它实际上将字符串绑定(bind)到 T0200并且总是进入你的match的第一个分支.模式匹配语言不允许您匹配这样的值名称。您可以匹配有区别的联合案例、文字值和其他一些东西。见 here .