模式匹配不调用 F# 中的函数

Question

open System

[<EntryPoint>]
let main argv =
    match argv with
        | [| firstArg |] -> printfn "Your first arg is %s", firstArg
        | [| |] -> failwith "You didn't pass an argument"
        | _ -> failwith "You did something unusual"
    0 // return an integer exit code

我写这个是为了处理我的 F# 控制台应用程序的第一个参数。如果我没有传递参数，它就会失败，并出现异常 "You didn't pass an argument"。如果我至少传递了两个参数，它会失败并出现异常 "You did something unusual"。但是，当我恰好通过一个参数时，它什么也没说。为什么 printfn 在这里不起作用？

Answer 1

这里没有打印任何东西的原因是你在 printf 之后添加了一个额外的逗号。这意味着签名是一个 string -> unit 函数和字符串元组。如果您删除逗号，它将起作用。

一个可行的解决方案是


[<EntryPoint>]
let main argv =
    match argv with
        | [| firstArg |] -> printfn "Your first arg is %s" firstArg
        | [| |] -> failwith "You didn't pass an argument"
        | _ -> failwith "You did something unusual"
    0 // return an integer exit code

您可能已经在运行之前看到编译器警告，它说 warning FS0020: The result of this expression has type '(string -> unit) * string' and is implicitly ignored. Consider using 'ignore' to discard this value explicitly, e.g. 'expr |> ignore', or 'let' to bind the result to a name, e.g. 'let result = expr'

模式匹配不调用 F# 中的函数

Pattern matching does not call function in F#

printf

f#

pattern-matching

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