f# - 文字属性不起作用

Question

在阅读完克里斯对F# - public literal的回答以及http://blogs.msdn.com/b/chrsmith/archive/2008/10/03/f-zen-the-literal-attribute.aspx上的博客文章后，我不明白为什么以下内容不起作用:

[<Literal>]
let one = 1

[<Literal>]
let two = 2

let trymatch x =
    match x with
    | one -> printfn "%A" one
    | two -> printfn "%A" two
    | _ -> printfn "none"


trymatch 3

尽管我认为不应该这样做，但它始终打印“3”。我在这里看不到什么？

Answer 1

我认为字面量必须为大写。以下工作正常:

[<Literal>]
let One = 1
[<Literal>]
let Two = 2

let trymatch x =
    match x with
    | One -> printfn "%A" One
    | Two -> printfn "%A" Two
    | _ -> printfn "none"


trymatch 3

另外，如果您想要一个很好的通用解决方案而不使用文字，可以定义一个参数化的 Activity 模式，如下所示:

let (|Equals|_|) expected actual = 
  if actual = expected then Some() else None

然后写

let one = 1
let two = 2

let trymatch x =
    match x with
    | Equals one -> printfn "%A" one
    | Equals two -> printfn "%A" two
    | _ -> printfn "none"