IegTools.Sequencer 3.0.0-rc.2

This is a prerelease version of IegTools.Sequencer.
dotnet add package IegTools.Sequencer --version 3.0.0-rc.2                
NuGet\Install-Package IegTools.Sequencer -Version 3.0.0-rc.2                
This command is intended to be used within the Package Manager Console in Visual Studio, as it uses the NuGet module's version of Install-Package.
<PackageReference Include="IegTools.Sequencer" Version="3.0.0-rc.2" />                
For projects that support PackageReference, copy this XML node into the project file to reference the package.
paket add IegTools.Sequencer --version 3.0.0-rc.2                
#r "nuget: IegTools.Sequencer, 3.0.0-rc.2"                
#r directive can be used in F# Interactive and Polyglot Notebooks. Copy this into the interactive tool or source code of the script to reference the package.
// Install IegTools.Sequencer as a Cake Addin
#addin nuget:?package=IegTools.Sequencer&version=3.0.0-rc.2&prerelease

// Install IegTools.Sequencer as a Cake Tool
#tool nuget:?package=IegTools.Sequencer&version=3.0.0-rc.2&prerelease                


IegTools.Sequencer provides a fluent interface for creating easy-to-read and extensible sequences, eliminating the need for lengthy if/else statements.
The library is written in C# 11.0 and targets .NET Standard 2.0 (.NET Core and .NET Framework).

The library allows you to define:

  • Transition jobs: from one state to another state, when it should be triggered, and the action that should be invoked.
  • Force state on specified conditions.
  • Invoke actions on specified states.

Build Status

  workflow tests
  workflow complete

Table of Contents

State Tags
SequenceBuilder Extensions
Version Changes
Breaking Changes


The library is available as a NuGet package.


Configure, build and run a sequence

Configuration .NET 6 style

A simple example configuration and usage for an OnTimer-sequence:

public class OnTimerExample
    private ISequence _sequence;
    public OnTimerExample() =>
        _sequence = SequenceConfig.Build();

    public void In(bool value)
        LastValue = value;


    private ISequenceBuilder SequenceConfig =>
            .AddForceState(">Off", () => !LastValue)
            .AddTransition(">Off", "PrepareOn", () => LastValue, () => _sequence.Stopwatch.Restart())
            .AddTransition("PrepareOn", "!On", () => _sequence.Stopwatch.Expired(MyTimeSpan));

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Configuration .NET 5 style

A more complex example configuration for a pump-anti-sticking-sequence:

 private ISequenceBuilder SequenceConfig =>
        SequenceBuilder.Configure(builder =>
            builder.AddForceState(">Paused", () => !_onTimer.Out);
            builder.AddTransition(">Paused", "Activated",
                () => _onTimer.Out,
                () => _countStarts = 1);
            builder.AddTransition("Activated", "Pump on",
                () => true,
                () => Stopwatch.Restart());
            builder.AddTransition("Pump on", "Pump off",
                () => Stopwatch.Expired(_settings.RunTime * _countStarts.Factorial()),
                () =>

            builder.AddTransition("Pump off", "Pump on",
                () => Stopwatch.Expired(_settings.PauseTime) && !sequenceDone());

            builder.AddTransition("Pump off", ">Paused",
                () => Stopwatch.Expired(_settings.PauseTime) && sequenceDone(),
                () => _onTimer.In(false));

            bool sequenceDone() => _countStarts > _settings.PumpStartQuantity;

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Config in Detail

  • Force state on condition:
    builder.AddForceState("ForceState", constraint)

  • State transition on condition (with optional action)
    builder.AddTransition("FromState", "ToState", constraint, action)

  • Action on state:
    builder.AddStateAction("State", action)

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States can be defined as strings or enums, internally they will be stored as strings.

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State Tags

[I tend to delete this feature, it's to much magic, the Initial-State and ignored States should be defined explicit.]

State-Tags can only be used with string-states. For enum-states there are other possibilities. (-> Validation Handler)

There are available two state tags as prefix for states

  • the IgnoreTag '!'
  • and the InitialStateTag '>'


Use the IgnoreTag as prefix for an state to tell the Validator not to check this state for counterpart-plausibility.


 .AddTransition("PrepareOff", "!Off", () => Stopwatch.Expired(MyTimeSpan));


Use the InitialStateTag as prefix for an state to tell the Sequence what state to start from.


 builder.AddForceState(">Paused", () => !_onTimer.Out);

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The sequence will be validated on build.
_sequence = builder.Build();

Validation Handler:

  • InitialState must be defined
  • The InitialState must have an counterpart in a StateTransition
  • The Sequence must have at least two steps
  • Each 'NextStep' must have a counterpart StateTransition with an matching 'CurrentState'
  • Each 'CurrentState' must have a counterpart StateTransition with an matching 'NextStep' or ForceState

Validation could be disabled

  • completely turn off validation

  • or with specifying states that shouldn't be validated:
    builder.DisableValidationForStates("state1", "state2", ...)
    builder.DisableValidationForStates(Enum.State1, Enum.State2, ...)

  • or with the IgnoreTag '!':
    .AddTransition("PrepareOn", "!On", ...);

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Internally the Framework is working with Handler (you can write your own customized handler). The Handler describe what they are supposed to do within the sequence.

There are five default handler at the moment:


The StateTransitionHandler is responsible for the transition between two states. It switches the sequence from start-state to end-state when the sequence current state is the start-state and the state-transition-condition is true. Additionally an action can be executed when the transition is done.


It's basically the same as the StateTransitionHandler, but it can handle multiple start-states to one end-state.


It's basically the same as the ContainsStateTransitionHandler, but it can handle all start-states that contains the specified string to one end-state.


Forces the sequence into the specified state when the force-state-condition is fulfilled. Additionally an action can be executed when the force-transition is done.


Executes continuously the specified action when the sequence is in the specified state.

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SequenceBuilder Extensions

ExtensionMethods for existing Handler

All existing Handler can be added to a sequence via the SequenceBuilders ExtensionMethods.


Each Transition can be enhanced with the ExtensionMethod .AllowOnceIn(timeSpan). This prevents the transition from being triggered again within the specified timeSpan.

Example from an xUnit test:

    public void Test_AllowOnlyOnceIn_set()
        var x = 0;
        var builder = SequenceBuilder.Configure(builder =>
            builder.AddTransition("State1", "State2", () => true, () => x++)

        var sut = builder.Build();


        for (int i = 0; i < 3; i++)


For more examples take a look at the UnitTests.

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Write your own customized

  • Handler
  • Sequence
  • and Validator

TODO Documentation

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Version Changes

v2.1 → v2.2

  • new builder.SetLogger(...) methods

v2.0 → v2.1

  • new ExtensionMethod .AllowOnceIn(timeSpan)

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Breaking Changes

so far none

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Product Compatible and additional computed target framework versions.
.NET net5.0 was computed.  net5.0-windows was computed.  net6.0 was computed.  net6.0-android was computed.  net6.0-ios was computed.  net6.0-maccatalyst was computed.  net6.0-macos was computed.  net6.0-tvos was computed.  net6.0-windows was computed.  net7.0 was computed.  net7.0-android was computed.  net7.0-ios was computed.  net7.0-maccatalyst was computed.  net7.0-macos was computed.  net7.0-tvos was computed.  net7.0-windows was computed.  net8.0 was computed.  net8.0-android was computed.  net8.0-browser was computed.  net8.0-ios was computed.  net8.0-maccatalyst was computed.  net8.0-macos was computed.  net8.0-tvos was computed.  net8.0-windows was computed. 
.NET Core netcoreapp2.0 was computed.  netcoreapp2.1 was computed.  netcoreapp2.2 was computed.  netcoreapp3.0 was computed.  netcoreapp3.1 was computed. 
.NET Standard netstandard2.0 is compatible.  netstandard2.1 was computed. 
.NET Framework net461 was computed.  net462 was computed.  net463 was computed.  net47 was computed.  net471 was computed.  net472 was computed.  net48 was computed.  net481 was computed. 
MonoAndroid monoandroid was computed. 
MonoMac monomac was computed. 
MonoTouch monotouch was computed. 
Tizen tizen40 was computed.  tizen60 was computed. 
Xamarin.iOS xamarinios was computed. 
Xamarin.Mac xamarinmac was computed. 
Xamarin.TVOS xamarintvos was computed. 
Xamarin.WatchOS xamarinwatchos was computed. 
Compatible target framework(s)
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NuGet packages

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Version Downloads Last updated
3.0.0-rc.2 131 12/26/2023
3.0.0-rc.1 73 12/24/2023
3.0.0-alpha.5 67 12/23/2023
3.0.0-alpha.4 79 12/17/2023
3.0.0-alpha.3 60 12/17/2023
3.0.0-alpha.2 77 12/14/2023
3.0.0-alpha.1 62 12/13/2023
2.2.2-alpha.4 74 12/11/2023
2.2.2-alpha.3 68 12/10/2023
2.2.2-alpha.2 65 12/10/2023
2.2.2-alpha 286 12/9/2023
2.2.1 426 12/7/2023
2.2.0 307 12/7/2023
2.1.0 374 11/2/2023
2.0.2 588 4/13/2023
2.0.2-rc.1 88 4/10/2023
2.0.2-beta2 502 3/28/2023
2.0.2-beta1 476 3/27/2023
2.0.2-beta.3 86 4/4/2023
1.10.1 611 3/18/2023
1.10.0 619 3/18/2023
1.9.0 630 2/21/2023
1.8.0 706 1/9/2023
1.7.0 806 8/2/2022
1.6.0 765 8/1/2022
1.5.0 788 6/16/2022

v3.0.0-rc.2 builder.SetOnStateChangedAction(...)