Dynamic Expresso Exception Handling

Exception handling helps you deal with any unexpected or exceptional situations that occur when a program is running. For example, you can use the try, catch, and finally keywords to try actions that may not succeed, handling failures, and cleaning up resources afterward.

If the syntax of the text is invalid or if there is an error during the parsing, it will throw a ParseException. A ParseException will be thrown whenever an expression cannot be compiled.

Let's consider the following simple example where the expression syntax is invalid.

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

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

    string expression = "x + y +";

    var result = interpreter.Eval(expression);

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

Let's run the above code, and you will see the following exception.

DynamicExpresso.Exceptions.ParseException: 'Invalid Operation (at index 7).'

You can use the try, catch blocks handles any kind of exceptions.

public static void Example2()
{
    try
    {
        Interpreter interpreter = new Interpreter();

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

        string expression = "x + y +";

        var result = interpreter.Eval(expression);

        Console.WriteLine("{0} = {1}", expression, result);
    }
    catch (ParseException e)
    {
        Console.WriteLine(e.Message);
    }
}

Let's consider another example where the expression uses a variable that is not defined.

public static void Example3()
{
    try
    {
        Interpreter interpreter = new Interpreter();
        string expression = "x + y + z";

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

        var result = interpreter.Eval(expression);

        Console.WriteLine("{0} = {1}", expression, result);
    }
    catch (ParseException e)
    {
        Console.WriteLine(e.Message);
    }
}

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

Unknown identifier 'z' (at index 8).