此值不是函数,无法应用 - F#

Question

// Learn more about F# at http://fsharp.org
// See the 'F# Tutorial' project for more help.

open System

let highLowGame () = 
    let rng = new Random()
    let secretNumber = rng.Next() % 100 + 1

    let rec highLowGameStep () = 
        printfn "Guess the secret number: " 
        let guessStr = Console.ReadLine()
        let guess = Int32.Parse(guessStr)

        match guess with
        | _ when guess > secretNumber
            -> (printfn "The secret number is lower")
                highLowGameStep ()
        | _ when guess = secretNumber
            -> (printfn "You've guessed correctly!")
                ()
        | _ when guess < secretNumber
            -> (printfn "The secret number is higher")
                highLowGameStep ()

    highLowGameStep ()

[<EntryPoint>]
let main argv = 
    printfn "%A" argv
    0 // return an integer exit code

我已经检查了这个代码一千次,我得到一个警告说g uess is incomplete on pattern matching这绝对是不可能的......我也得到一个错误说value is not a function and cannot be applied.

我直接从书中复制了这个,所以我不明白这是怎么编译的？!

Answer 1

模式匹配上的空白区域是错误的.它应该是这样的:

match guess with
| _ when guess > secretNumber ->
        (printfn "The secret number is lower")
        highLowGameStep ()
| _ when guess = secretNumber ->
        (printfn "You've guessed correctly!")
        ()
| _ when guess < secretNumber ->
        (printfn "The secret number is higher")
        highLowGameStep ()

这修复了编译错误.至于警告,编译器正在做出最好的猜测,但它无法确定所有案例是否实际被覆盖.如果要修复警告,可以添加另一个案例:

| _ -> invalidOp("Invalid input")