ReflectionContextTests.cs

class MyLibrary
{
    public MyLibrary()
    {
        pi = Math.PI;
    }

    public double pi { get; private set; }
    public double r { get; set; }

    public double rectArea(double width, double height)
    {
        return width * height;
    }

    public double rectPerimeter(double width, double height)
    {
        return (width + height) * 2;
    }
}

[TestMethod]
public void Reflection()
{
    // Create a library of helper function
    var lib = new MyLibrary();
    lib.r = 10;

    // Create a context that uses the library
    var ctx = new ReflectionContext(lib);

    // Test
    Assert.AreEqual(Parser.Parse("rectArea(10,20)").Eval(ctx), 200);
    Assert.AreEqual(Parser.Parse("rectPerimeter(10,20)").Eval(ctx), 60);
    Assert.AreEqual(Parser.Parse("2 * pi * r").Eval(ctx), 2 * Math.PI * 10);
}