IcedTasks

What is IcedTasks?

This library contains additional computation expressions for the task CE utilizing the Resumable Code introduced in F# 6.0.

• ValueTask<'T> - This utilizes .NET's ValueTask (which is essentially a Discriminated Union of 'Value | Task<'Value>) for possibly better performance in synchronous scenarios. Similar to F#'s Task Expression

  • valueTask
  • valueTaskUnit
  • poolingValueTask

• ColdTask<'T> - Alias for unit -> Task<'T>. Allows for lazy evaluation (also known as Cold) of the tasks, similar to F#'s Async being cold.

  • coldTask

• CancellableTask<'T> - Alias for CancellationToken -> Task<'T>. Allows for lazy evaluation (also known as Cold) of the tasks, similar to F#'s Async being cold. Additionally, allows for flowing a CancellationToken through the computation, similar to F#'s Async cancellation support.

  • cancellableTask
  • cancellableBackgroundTask

• CancellableValueTask<'T> - Alias for CancellationToken -> ValueTask<'T>. Allows for lazy evaluation (also known as Cold) of the tasks, similar to F#'s Async being cold. Additionally, allows for flowing a CancellationToken through the computation, similar to F#'s Async cancellation support.

  • cancellableValueTask
  • cancellablePoolingValueTask

• ParallelAsync<'T> - Utilizes the applicative syntax to allow parallel execution of Async<'T> expressions. See this discussion as to why this is a separate computation expression.

  • parallelAsync

• AsyncEx<'T> - Variation of F# async semantics described further below with examples.

  • asyncEx
  • This can also be accessed under IcedTasks.Polyfill.Async which will shadow the F# Async CE.
    • async

• Task<'T> - Polyfill for fixes to F# Task CE. Can be accessed under IcedTasks.Polyfill.Task which will shadow the F# Task CE.

  • task
  • backgroundTask

• Task - a CE for a Task that has no return value.

  • taskUnit
  • backgroundTaskUnit

Differences at a glance

• ¹ - Computation Expression
• ² - Which Nuget package do they come from
• ³ - Which Target Framework Moniker these are available in
• ⁴ - Hot refers to the asynchronous code block already been started and will eventually produce a value. Cold refers to the asynchronous code block that is not started and must be started explicitly by caller code. See F# Async Tutorial and Asynchronous C# and F# (II.): How do they differ? for more info.
• ⁵ - ValueTask Awaiting patterns
• ⁶ - Multi-start refers to being able to start the asynchronous code block again. See FAQ on Task Start for more info.
• ⁷ - Allows use of let rec with the computation expression. See Tail call Recursion for more info.
• ⁸ - CancellationToken is propagated to all types the support implicit CancellatationToken passing. Calling cancellableTask { ... } nested inside async { ... } (or any of those combinations) will use the CancellationToken from when the code was started.
• ⁹ - Cancellation will be checked before binds and runs.
• ¹⁰ - Allows parallel execution of the asynchronous code using the Applicative Syntax in computation expressions.
• ¹¹ - Allows use of IAsyncDisposable with the computation expression. See IAsyncDisposable for more info.

Why should I use this?

AsyncEx

AsyncEx is similar to Async except in the following ways:

1. Allows use for IAsyncDisposable

   open IcedTasks
   let fakeDisposable () = { new IAsyncDisposable with member __.DisposeAsync() = ValueTask.CompletedTask }
   
   let myAsyncEx = asyncEx {
       use _ = fakeDisposable ()
       return 42
   }

2. Allows let!/do! against Tasks/ValueTasks/any Awaitable

   open IcedTasks
   let myAsyncEx = asyncEx {
       let! _ = task { return 42 } // Task<T>
       let! _ = valueTask { return 42 } // ValueTask<T>
       let! _ = Task.Yield() // YieldAwaitable
       return 42
   }

3. When Tasks throw exceptions they will use the behavior described in Async.Await overload (esp. AwaitTask without throwing AggregateException

   let data = "lol"
   
   let inner = asyncEx {
       do!
           task {
               do! Task.Yield()
               raise (ArgumentException "foo")
               return data
           }
           :> Task
   }
   
   let outer = asyncEx {
       try
           do! inner
           return ()
       with
       | :? ArgumentException ->
           // Should be this exception and not AggregationException
           return ()
       | ex ->
           return raise (Exception("Should not throw this type of exception", ex))
   }

4. Use IAsyncEnumerable with for keyword. This example uses TaskSeq but you can use any IAsyncEnumerable<T>.

   open IcedTasks
   open FSharp.Control
   let myAsyncEx = asyncEx {
       let items = taskSeq {  // IAsyncEnumerable<T>
           yield 42
           do! Task.Delay(100)
           yield 1701
       }
       let mutable sum = 0
       for i in items do
           sum <- sum + i
       return sum
   }

For ValueTasks

• F# doesn't currently have a valueTask computation expression. Until this PR is merged.

open IcedTasks

let myValueTask = task {
    let! theAnswer = valueTask { return 42 }
    return theAnswer
}

For Cold & CancellableTasks

• You want control over when your tasks are started
• You want to be able to re-run these executable tasks
• You don't want to pollute your methods/functions with extra CancellationToken parameters
• You want the computation to handle checking cancellation before every bind.

ColdTask

Short example:

open IcedTasks

let coldTask_dont_start_immediately = task {
    let mutable someValue = null
    let fooColdTask = coldTask { someValue <- 42 }
    do! Async.Sleep(100)
    // ColdTasks will not execute until they are called, similar to how Async works
    Expect.equal someValue null ""
    // Calling fooColdTask will start to execute it
    do! fooColdTask ()
    Expect.equal someValue 42 ""
}

CancellableTask & CancellableValueTask

The examples show cancellableTask but cancellableValueTask can be swapped in.

Accessing the context's CancellationToken:

1. Binding against CancellationToken -> Task<_>

   let writeJunkToFile = 
       let path = Path.GetTempFileName()
   
       cancellableTask {
           let junk = Array.zeroCreate bufferSize
           use file = File.Create(path)
   
           for i = 1 to manyIterations do
               // You can do! directly against a function with the signature of `CancellationToken -> Task<_>` to access the context's `CancellationToken`. This is slightly more performant.
               do! fun ct -> file.WriteAsync(junk, 0, junk.Length, ct)
       }

2. Binding against CancellableTask.getCancellationToken

   let writeJunkToFile = 
       let path = Path.GetTempFileName()
   
       cancellableTask {
           let junk = Array.zeroCreate bufferSize
           use file = File.Create(path)
           // You can bind against `CancellableTask.getCancellationToken` to get the current context's `CancellationToken`.
           let! ct = CancellableTask.getCancellationToken ()
           for i = 1 to manyIterations do
               do! file.WriteAsync(junk, 0, junk.Length, ct)
       }

Short example:

let executeWriting = task {
    // CancellableTask is an alias for `CancellationToken -> Task<_>` so we'll need to pass in a `CancellationToken`.
    // For this example we'll use a `CancellationTokenSource` but if you were using something like ASP.NET, passing in `httpContext.RequestAborted` would be appropriate.
    use cts = new CancellationTokenSource()
    // call writeJunkToFile from our previous example
    do! writeJunkToFile cts.Token
}

ParallelAsync

• When you want to execute multiple asyncs in parallel and wait for all of them to complete.

Short example:

open IcedTasks

let exampleHttpCall url = async {
    // Pretend we're executing an HttpClient call
    return 42
}

let getDataFromAFewSites = parallelAsync {
    let! result1 = exampleHttpCall "howManyPlantsDoIOwn"
    and! result2 = exampleHttpCall "whatsTheTemperature"
    and! result3 = exampleHttpCall "whereIsMyPhone"

    // Do something meaningful with results
    return ()
}

Builds

GitHub Actions

NuGet

Package	Stable	Prerelease
IcedTasks

Developing

Make sure the following requirements are installed on your system:

• dotnet SDK 7.0 or higher

or

• VSCode Dev Container

Environment Variables

• CONFIGURATION will set the configuration of the dotnet commands. If not set, it will default to Release.
  • CONFIGURATION=Debug ./build.sh will result in -c additions to commands such as in dotnet build -c Debug
• GITHUB_TOKEN will be used to upload release notes and Nuget packages to GitHub.
  • Be sure to set this before releasing
• DISABLE_COVERAGE Will disable running code coverage metrics. AltCover can have severe performance degradation so it's worth disabling when looking to do a quicker feedback loop.
  • DISABLE_COVERAGE=1 ./build.sh

Building

> build.cmd <optional buildtarget> // on windows
$ ./build.sh  <optional buildtarget>// on unix

The bin of your library should look similar to:

$ tree src/MyCoolNewLib/bin/
src/MyCoolNewLib/bin/
└── Debug
    └── net50
        ├── MyCoolNewLib.deps.json
        ├── MyCoolNewLib.dll
        ├── MyCoolNewLib.pdb
        └── MyCoolNewLib.xml

Build Targets

• Clean - Cleans artifact and temp directories.
• DotnetRestore - Runs dotnet restore on the solution file.
• DotnetBuild - Runs dotnet build on the solution file.
• DotnetTest - Runs dotnet test on the solution file.
• GenerateCoverageReport - Code coverage is run during DotnetTest and this generates a report via ReportGenerator.
• WatchTests - Runs dotnet watch with the test projects. Useful for rapid feedback loops.
• GenerateAssemblyInfo - Generates AssemblyInfo for libraries.
• DotnetPack - Runs dotnet pack. This includes running Source Link.
• SourceLinkTest - Runs a Source Link test tool to verify Source Links were properly generated.
• PublishToNuGet - Publishes the NuGet packages generated in DotnetPack to NuGet via paket push.
• GitRelease - Creates a commit message with the Release Notes and a git tag via the version in the Release Notes.
• GitHubRelease - Publishes a GitHub Release with the Release Notes and any NuGet packages.
• FormatCode - Runs Fantomas on the solution file.
• BuildDocs - Generates Documentation from docsSrc and the XML Documentation Comments from your libraries in src.
• WatchDocs - Generates documentation and starts a webserver locally. It will rebuild and hot reload if it detects any changes made to docsSrc files, libraries in src, or the docsTool itself.
• ReleaseDocs - Will stage, commit, and push docs generated in the BuildDocs target.
• Release - Task that runs all release type tasks such as PublishToNuGet, GitRelease, ReleaseDocs, and GitHubRelease. Make sure to read Releasing to setup your environment correctly for releases.

Releasing

• Start a git repo with a remote

git add .
git commit -m "Scaffold"
git remote add origin https://github.com/user/MyCoolNewLib.git
git push -u origin master

• Create your NuGeT API key

  • Add your NuGet API key to paket

  paket config add-token "https://www.nuget.org" 4003d786-cc37-4004-bfdf-c4f3e8ef9b3a

  • or set the environment variable NUGET_TOKEN to your key

• Create a GitHub OAuth Token

  • You can then set the environment variable GITHUB_TOKEN to upload release notes and artifacts to github
  • Otherwise it will fallback to username/password

• Then update the CHANGELOG.md with an "Unreleased" section containing release notes for this version, in KeepAChangelog format.

NOTE: Its highly recommend to add a link to the Pull Request next to the release note that it affects. The reason for this is when the RELEASE target is run, it will add these new notes into the body of git commit. GitHub will notice the links and will update the Pull Request with what commit referenced it saying "added a commit that referenced this pull request". Since the build script automates the commit message, it will say "Bump Version to x.y.z". The benefit of this is when users goto a Pull Request, it will be clear when and which version those code changes released. Also when reading the CHANGELOG, if someone is curious about how or why those changes were made, they can easily discover the work and discussions.

Here's an example of adding an "Unreleased" section to a CHANGELOG.md with a 0.1.0 section already released.

## [Unreleased]

### Added
- Does cool stuff!

### Fixed
- Fixes that silly oversight

## [0.1.0] - 2017-03-17
First release

### Added
- This release already has lots of features

[Unreleased]: https://github.com/user/MyCoolNewLib.git/compare/v0.1.0...HEAD
[0.1.0]: https://github.com/user/MyCoolNewLib.git/releases/tag/v0.1.0

• You can then use the Release target, specifying the version number either in the RELEASE_VERSION environment variable, or else as a parameter after the target name. This will:
  • update CHANGELOG.md, moving changes from the Unreleased section into a new 0.2.0 section
    • if there were any prerelease versions of 0.2.0 in the changelog, it will also collect their changes into the final 0.2.0 entry
  • make a commit bumping the version: Bump version to 0.2.0 and adds the new changelog section to the commit's body
  • publish the package to NuGet
  • push a git tag
  • create a GitHub release for that git tag

macOS/Linux Parameter:

./build.sh Release 0.2.0

macOS/Linux Environment Variable:

RELEASE_VERSION=0.2.0 ./build.sh Release