Expressif provides a class named Expression to define a chain of functions applied to a value. The class is expecting the textual representation of the chained functions in its constructor.
var expression = new Expression("lower");
var result = expression.Evaluate("Nikola Tesla");
Assert.That(result, Is.EqualTo("nikola tesla"));
Some functions require parameters, you can specify them between the parenthesis following the function name. Note that literal textual values don’t required quotes surronding them.
var expression = new Expression("remove-chars(a)");
var result = expression.Evaluate("Nikola Tesla");
Assert.That(result, Is.EqualTo("Nikol Tesl"));
You can chain the functions with the operator pipe (|). The functions are executed from left to right.
var expression = new Expression("lower | remove-chars(a)");
var result = expression.Evaluate("Nikola Tesla");
Assert.That(result, Is.EqualTo("nikol tesl"));
It’s possible to use variables as function parameters. The name of the variables must always start by an arobas (@)
var context = new Context();
context.Variables.Add<char>("myChar", 'k');
var expression = new Expression("lower | remove-chars(@myChar)", context);
var result = expression.Evaluate("Nikola Tesla");
Assert.That(result, Is.EqualTo("niola tesla"));
In addition to the variables that must be scalar values (text, numeric, dateTime …), you can also add a property-object to the context. A property-object must be a pure C# object, an IDictionnary, an IList, or a DataRow. You can access the properties of the property-object based on the property’s name with the syntax [property-name].
var context = new Context();
context.CurrentObject.Set(new { CharToBeRemoved = 't' });
var expression = new Expression("lower | remove-chars([CharToBeRemoved])", context);
var result = expression.Evaluate("Nikola Tesla");
Assert.That(result, Is.EqualTo("nikola esla"));
or based on its position with the syntax #index (where index is positive number).
var context = new Context();
context.CurrentObject.Set(new List<char>() { 'e', 's' });
var expression = new Expression("lower | remove-chars(#1)", context);
var result = expression.Evaluate("Nikola Tesla");
Assert.That(result, Is.EqualTo("nikola tela"));
It’s also possible to use the result of function as the value of a parameter for another function. To achieve this the function as a parameter must be surrounded by curly braces {...}.
var context = new Context();
context.Variables.Add<int>("myVar", 6);
context.CurrentObject.Set(new List<int>() { 15, 8, 3 });
var expression = new Expression("lower | skip-last-chars( {@myVar | subtract(#2) })", context);
var result = expression.Evaluate("Nikola Tesla");
Assert.That(result, Is.EqualTo("nikola te"));
