Why are some of the FAKE methods not working as part of the target functions?

Question

Consider the following:

#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"

The above script works fine, but when I move Shell.Exec to Target like this:

#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"

As a result, I get an error message:

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 [e-mail](String arg00) in C:\code\fake\paket-files\matthid\Yaaf.FSharp.Scripting\src\source\Yaaf.FSharp.Scripting\YaafFSharpScripting.fs:line 1303
   at [e-mail](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 Yaaf.FSharp.Scripting.Helper.redirectOut@1247[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 [e-mail](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 [e-mail](String text) in C:\code\fake\paket-files\matthid\Yaaf.FSharp.Scripting\src\source\Yaaf.FSharp.Scripting\YaafFSharpScripting.fs:line 1284
   at [e-mail]-FSharp-Scripting-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

Here I want to make a shell command only for a specific purpose. Ignore the mkdir command as I really would like to use the schtasks command. I just used mkdir for simplicity. Maybe there is a nuance that I miss here. I also noticed the same behavior using environmentVarOrFail. Thanks in advance to everyone who answers.

Answer 1

Shell.Exec int, Target , unit.

:

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

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

"" , - , int, , unit.

: : ", , int? ?"

, , . , Shell.Exec , . , , - ignore.

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

, . Shell.Exec, : ", , , , ignore it."

---

, . script . , , FileUtils.mkdir:

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