爲什麼一些FAKE方法不能在目標函數中工作？

考慮以下幾點：爲什麼一些FAKE方法不能在目標函數中工作？

#r @"FakeLib.dll" 

open Fake 
open Fake.StringHelper 
open Fake.ProcessHelper 

Shell.Exec("mkdir","exampleDirectory") 

Target "DoStuff" (fun() -> 
    trace "Doing Stuff..." 
) 

Target "Clean" (fun() -> 
    trace "Cleaning..." 
) 

Target "Deploy" (fun() -> 
    trace "Deploying..." 
) 

"DoStuff" 
    ==>"Clean" 
    ==>"Deploy" 

RunTargetOrDefault "Deploy"

上述腳本工作正常，但是當我移動Shell.Exec一個目標內是這樣的：

#r @"FakeLib.dll" 

open Fake 
open Fake.StringHelper 
open Fake.ProcessHelper 

Target "DoStuff" (fun() -> 
    trace "Doing Stuff..." 
    Shell.Exec("mkdir","exampleDirectory") 
) 

Target "Clean" (fun() -> 
    trace "Cleaning..." 
) 

Target "Deploy" (fun() -> 
    trace "Deploying..." 
) 

"DoStuff" 
    ==>"Clean" 
    ==>"Deploy" 

RunTargetOrDefault "Deploy"

我結束了一個錯誤：

FsiEvaluationException: 

Error: 

     DeployScript.fsx(10,5): error FS0001: This expression was expected to have type 
      unit 
     but here has type 
      int 


Output: [Loading C:\Users\myusername\Desktop\SomeFolder\DeployScript.fsx] 


Input: C:\Users\myusername\Desktop\SomeFolder\DeployScript.fsx 
\Arguments: 
    C:\fsi.exe 

Exception: Yaaf.FSharp.Scripting.FsiEvaluationException: Error while compiling or executing fsharp snippet. ---> System.Exception: Operation failed. The error text has been print the error stream. To return the corresponding FSharpErrorInfo use the EvalInteractionNonThrowing, EvalScriptNonThrowing or EvalExpressionNonThrowing 
    at Microsoft.FSharp.Compiler.Interactive.Shell.FsiEvaluationSession.commitResult[a,b](FSharpChoice`2 res) 
    at Microsoft.FSharp.Compiler.Interactive.Shell.FsiEvaluationSession.EvalScript(String filePath) 
    at [email protected](String arg00) in C:\code\fake\paket-files\matthid\Yaaf.FSharp.Scripting\src\source\Yaaf.FSharp.Scripting\YaafFSharpScripting.fs:line 1303 
    at [email protected](Unit unitVar0) in C:\code\fake\paket-files\matthid\Yaaf.FSharp.Scripting\src\source\Yaaf.FSharp.Scripting\YaafFSharpScripting.fs:line 1277 
    at Yaaf.FSharp.Scripting.Helper.consoleCapture[a](TextWriter out, TextWriter err, FSharpFunc`2 f) in C:\code\fake\paket-files\matthid\Yaaf.FSharp.Scripting\src\source\Yaaf.FSharp.Scripting\YaafFSharpScripting.fs:line 1221 
    at [email protected][a](Boolean preventStdOut, OutStreamHelper out, OutStreamHelper err, FSharpFunc`2 f) in C:\code\fake\paket-files\matthid\Yaaf.FSharp.Scripting\src\source\Yaaf.FSharp.Scripting\YaafFSharpScripting.fs:line 1254 
    at [email protected](String text) in C:\code\fake\paket-files\matthid\Yaaf.FSharp.Scripting\src\source\Yaaf.FSharp.Scripting\YaafFSharpScripting.fs:line 1276 
    --- End of inner exception stack trace --- 
    at [email protected](String text) in C:\code\fake\paket-files\matthid\Yaaf.FSharp.Scripting\src\source\Yaaf.FSharp.Scripting\YaafFSharpScripting.fs:line 1284 
    at [email protected]IFsiSession-EvalScriptWithOutput(String) in C:\code\fake\paket-files\matthid\Yaaf.FSharp.Scripting\src\source\Yaaf.FSharp.Scripting\YaafFSharpScripting.fs:line 1308 
    at Fake.FSIHelper.runScriptUncached(Boolean useCache, String scriptPath, IEnumerable`1 fsiOptions, Boolean printDetails, CacheInfo cacheInfo, TextWriter out, TextWriter err) in C:\code\fake\src\app\FakeLib\FSIHelper.fs:line 471 
DeployScript.fsx(10,5): error FS0001: This expression was expected to have type

這裏的一點是我試圖只在某個目標下執行shell命令。不要關注mkdir命令，因爲我實際上想要使用schtasks命令。我只是爲了簡單起見而使用了mkdir。也許我在這裏錯過了一個細微差別。我也注意到使用environVarOrFail時的相同行爲。預先感謝所有回覆的人。

來源

2017-07-06 Leroy Jenkins Coder

Shell.Exec返回int，但Target需要返回unit的函數。

試試這個：

let returnUnit() =() 
let return42() = 42 

Target "One" returnUnit // works 
Target "Two" return42 // fails: expected to have type unit, but here has type int

目標「兩個」編譯失敗，因爲它的第二個參數是返回int的函數，而返回unit預期的功能。

這個錯誤是爲了防止你忘記函數返回值：編譯器有用地告訴你「嘿，你確定你不想用這個int做什麼嗎？那麼爲什麼你在第一個函數中調用函數地點？」

但是，有時候，丟棄返回值是有意義的。例如，在這種特殊情況下，您稱Shell.Exec爲副作用，其返回值並不令您感興趣。這種情況經常出乎意料地發生，所以經常有這樣的特殊功能 - ignore。

Target "DoStuff" (fun() -> 
    trace "Doing Stuff..." 
    Shell.Exec("mkdir","exampleDirectory") |> ignore // compiles fine 
)

該函數獲取任何值，將其拋出並返回一個單位。通過將其應用於Shell.Exec的結果，您告訴編譯器：「是的，我確定我不需要這個值，請ignore它。」

這就是說，我強烈建議使用專門的功能，而不是通用的系統調用。這將使您的腳本更具可讀性，甚至可以幫助您儘早發現偶然的錯誤。例如，要創建目錄，請使用FileUtils.mkdir：

Target "DoStuff" (fun() -> 
    trace "Doing Stuff..." 
    FileUtils.mkdir "exampleDirectory" // no need for `ignore`, mkdir already returns `unit` 
)

來源

2017-07-06 02:55:26

非常感謝。我不打算使用mkdir系統調用。我需要它用於schtasks命令。我找不到FAKE中的任何內容來創建，結束和刪除計劃任務。所以，我將使用Shell.Exec來完成這個任務。 –

爲什麼一些FAKE方法不能在目標函數中工作？

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