Dynamic Expresso Variables

The Dynamic Expresso library provides the following standard constants, which you can use directly in the expressions.

You can also define your custom variables by using the SetVariable method of Interpreter. The following example adds two variables x and y, to use them inside an expression.

public static void Example1()
{
    Interpreter interpreter = new Interpreter();

    interpreter.SetVariable("x", 6);
    interpreter.SetVariable("y", 5.5);

    string expression = "x + y * (x - y)";
    var result = interpreter.Eval(expression);

    Console.WriteLine("{0} = {1}", expression, result);
}

Dynamic Expresso is statically typed. It knows the type of each variable based on the value.

public static void Example2()
{
    Interpreter interpreter = new Interpreter();
    interpreter.SetVariable("myInt", 6);
    interpreter.SetVariable("myDouble", -3.6);
    interpreter.SetVariable("myStr", "Hello World");
    interpreter.SetVariable("myArray", new object[] { 3.5, "Test", false });

    List<string> expressions = new List<string>()
    {
        "myInt + myDouble",
        "myStr + \", you are learning Expression Evaluator\"",
        "myArray.Length",
        "myArray[0]",
        "myArray[2]",
    };

    foreach (var expression in expressions)
    {
        var result = interpreter.Eval(expression);
        Console.WriteLine("{0} = {1}", expression, result);
    }
}

Let's execute the above code, and you will see the following output.

myInt + myDouble = 2.4
myStr + ", you are learning Expression Evaluator" = Hello World, you are learning Expression Evaluator
myArray.Length = 3
myArray[0] = 3.5
myArray[2] = False

Variables can be primitive types or custom complex types such as classes, structures, delegates, arrays, collections, etc.

You can use custom functions with delegate variables using the Interpreter.SetFunction method.

public static void Example3()
{
    Func<double, double, double> pow = (x, y) => Math.Pow(x, y);
    Interpreter interpreter = new Interpreter();
    interpreter.SetFunction("pow", pow);

    List<string> expressions = new List<string>()
    {
        "pow(1, 2)",
        "pow(2, 2)",
        "pow(3, 2)",
        "pow(4, 2)",
        "pow(5, 2)",
    };

    foreach (var expression in expressions)
    {
        var result = interpreter.Eval(expression);
        Console.WriteLine("{0} = {1}", expression, result);
    }
}