Expressif 0.2.20

Expressif

Expressif is the variable substitution syntax, initially designed for NBi.io.

Expressif allows you to define variables and transformation of these variables (functions), in plain text, which can then be interpreted by the engine. The syntax for the definition of the expression transforming the variable is similar to:

@myVariable | text-to-lower | text-to-pad-right(@myCount, *)

About | Quickstart | Installing | Functions and predicates

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Quickstart

Expressif provides a class named Expression to define a chain of functions to apply 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 | numeric-to-subtract(#2) })", context);
var result = expression.Evaluate("Nikola Tesla");
Assert.That(result, Is.EqualTo("nikola te"));

Installing

Install in the usual .NET fashion:

Install-Package Expressif

Supported functions and predicates

Functions

Predicates