delegateas/ExpressionEngine

Expression Engine for Power Automate expressions written in C# using Sprache!

ExpressionEngine

ExpressionEngine is originally created in PowerAutomateMockUp to parse PowerAutomate Expressions. Parsing of expression can be used outside of Power Automate, why the ExpressionEngine is now a standalone project.

Usage

EE uses Dependency Injection, which makes it easy to use and extend. Out-of-the-box functionality comes from the AddExpressionEngine() extension method:

using Microsoft.Extensions.DependencyInjection;
using Parser;
...
var services = new ServiceCollection();
services.AddExpressionEngine();
var sp = services.BuildServiceProvider();

ee = sp.GetRequiredService<IExpressionEngine>();

EE can evaluate expression to a string or a ValueContainer. A ValueContainer can contain boolean, integer, float, string, object, array or null values.

var str = ee.Parse("@concat('Hello', ' ', 'World', '!'"); // str = "Hello World!"
var strVc = ee.ParseToValueContainer("@concat('Hello', ' ', 'World', '!'").GetValue<string>(); // str = "Hello World!"

⚠️ Expressions can also be written inside strings, such as someone@@@{toLower('DELEGATE')}.dk will evaluate to someone@delegate.dk, the result using @{<expression>} will always evaluate to a ValueType.String, whereas @<expression> will evaluate to the actual type.

Extending with custom functions

Write your function by extending the Function class and providing a function name:

public class FooBar : Function
{
    public FooBar() : base("fooBar") { }
    
    public override ValueContainer ExecuteFunction(params ValueContainer[] parameters)
    {
        if (parameters.Length != 1)
            throw new Exception("Expected 1 argument");
        if (parameters[0].Type() != ValueContainer.ValueType.String)
            throw new Exception("Expected string");
        return new ValueContainer($"Foo - {parameters[0].GetValue<string>()} - Bar");
    }
}

Then add the function to the service collection

services.AddTransient<IFunction, FooBar>();

IFunction is used to apply the function when the fooBar function name is evaluated.

Contributing

CI/CD is configured using Github Actions and it works by analyzing commit messages to determine the changes and the relevant version number. This is done using semantic-release and the commit message style is Conventional Commits. Please use the correct format in every commit message to ensure the version is determined correctly

The main branch is the release branch which will release a production NuGet package with the determined version number. The dev branch is the development branch and will release a development NuGet package with the determined version number.

Therefore, start by making a pull-request against dev which will trigger a pre-release and later on we can make a production release.