Dynamic Expressions

The Extensions.Expressions package provides runtime expression evaluation and template rendering.

Installation

dotnet add package WorkflowFramework.Extensions.Expressions

SimpleExpressionEvaluator

A lightweight evaluator supporting variables, comparisons, boolean logic, arithmetic, and literals:

using WorkflowFramework.Extensions.Expressions;

var evaluator = new SimpleExpressionEvaluator();
var vars = new Dictionary<string, object?> { ["age"] = 25, ["threshold"] = 18 };

var result = await evaluator.EvaluateAsync<bool>("age >= threshold", vars);
// true

Supported Operations

• Comparisons: ==, !=, >, <, >=, <=
• Boolean: &&, ||
• Arithmetic: +, -, *, /
• Literals: numbers, true/false, null, quoted strings
• Variables: any key from the variables dictionary

TemplateEngine

Renders strings with {{expression}} placeholders:

var engine = new TemplateEngine();
var vars = new Dictionary<string, object?> { ["name"] = "Alice", ["total"] = 42.5 };

var output = await engine.RenderAsync("Hello {{name}}, your total is {{total}}.", vars);
// "Hello Alice, your total is 42.5."

IfExpression Builder

Use expressions directly in workflow branching:

using WorkflowFramework.Extensions.Expressions;

var workflow = new WorkflowBuilder()
    .IfExpression("amount > 1000")
        .Step(requireApproval)
    .Else()
        .Step(autoApprove)
    .EndIf()
    .Build();

The expression is evaluated against the workflow context properties at runtime.

Custom Evaluators

Implement IExpressionEvaluator for more advanced scenarios (e.g., C# scripting, JavaScript):

public interface IExpressionEvaluator
{
    string Name { get; }
    Task<T?> EvaluateAsync<T>(string expression, IDictionary<string, object?> variables, CancellationToken ct = default);
    Task<object?> EvaluateAsync(string expression, IDictionary<string, object?> variables, CancellationToken ct = default);
}