RuntimeExpressions

Simple .net standard runtime expression evaluation

A simple, extensible expression evaluator. The evaluator accepts string expressions and evaluates the expression value. the EvaluationEngine is the main class that does the evaluation, and it optionally accepts implementations of IFunctionEvaluator and IVariableEvaluator that act as extension points to allow evluating custom defined functions and variables. Below are some examples of basic use cases, all shown in C#

Usage examples:

var engine = new RuntimeExpressions.EvaluationEngine();
Console.WriteLine(engine.Evaluate<int>("10 + 2"); //12
Console.WriteLine(engine.Evaluate<decimal>("1.1 + (2 * 4) - 0.1"); //9.0
Console.WriteLine(engine.Evaluate<string>("\"Hello, \" + \"world!\""); //Hello, world!
Console.WriteLine(engine.Evaluate<string>("\"ABAABCD\" - \"AB\""); //ACD

Can be extended with user-defined functions by implementing IFunctionEvaluator and passing instance(s) of the implementation(s) to the contructor of EvaluationEngine. Usage example:

public class ExtraFuncProvider : IFunctionEvaluator
{
    public int Order => 1;

    public EvaluationResult Evaluate(string functionName, IList<object> args)
    {
        if (args != null && args.Count == 1 && decimal.TryParse(args[0].ToString(), out var x))
        {
            switch (functionName.ToLower())
            {
                case "reverse":
                    return new EvaluationResult(decimal.Parse(new string(x.ToString().Reverse().ToArray())));
                case "negate":
                    return new EvaluationResult(-1 * x);
                default:
                    return EvaluationResult.NotEvaluated;
            }
        }

        return EvaluationResult.NotEvaluated;
    }
}

/*..*/
_engine = new EvaluationEngine(null, new[] { new ExtraFuncProvider() });
Console.WriteLine(_engine.Evaluate<double>("Reverse(194)")); //491
Console.WriteLine(_engine.Evaluate<double>("Negate(11)")); //-11

Also supports variables that will be evaluated using implemenataions of IVariableEvaluator. A Basic dictionary-based implementation is provided in the class DictionaryVariableProvider. Usage example:

var varProvider = new DictionaryVariableProvider(new Dictionary<string, object>
{
    ["V1"] = 2,
    ["V2"] = 2.5
});

_engine = new EvaluationEngine(new[] { varProvider }, null);           
Console.WriteLine(_engine.Evaluate<decimal>("V1 * V2 + 0.5")); //5.5