In the past few days I’ve created two new library projects: Parrot-Test and Parrot-Container. The goal of each of these two projects was to provide a set of reusable libraries for people to make some common tasks easier and enable easy use of best practices.

While working on Parrot-Container I realized that I wanted to use Parrot-Test to implement the hest harness and test suite. While working on Parrot-Test I realized that I really wanted to use some of the decoupling and new event-based features of Parrot-Container. Also, once I started adding an events library to Parrot-Container, I realized that project was much more than just a dependency injection container project and really needed to be renamed to show that it was bigger. Proper mock objects for Parrot-Test were also going to require a proxy object library, which didn’t even have a home yet.

In short I have a lot of little things I wanted to do, these two libraries really were only small parts of my larger overall plans, and many of the little things I am working on have lots of opportunity for code sharing.

Today I’ve merged those two projects together into a new project called Rosella. Rosella is a library-of-libraries project, where I aim to provide a series of reasonably-sized building block libraries for people to use. Rosella is not a framework per say. It’s more modular than that. At the moment it is a collection of about 5 libraries (and growing) that can be used independently of each other. There are opportunities for interplay and code reuse, but I am trying to keep each individual building block as small as is usefully possible. Pick what you want, leave what you don’t, and be empowered by having these cool new tools at your disposal. Here’s a quick rundown of what Rosella offers right now:


Actions are bundled-up commands that can be created once and executed later on a target object. In the most simple case, Rosella::Action::Method, the action is a method call on the given invocant with a pre-specified list of parameters. Once you have the Action object all bundled up, you can pass it around and call it any time you want.

Arguments to an Action are themselves complicated objects which provide resolution behavior: when you ask for the appropriate value, it may return it directly, calculate it, search for it, etc. If you’re using the Action library with the Container library (described below), there is an action argument type that looks up the value in the container.

Actions are useful because you can package up some kind of command that you want to execute, store it for later, and execute it whenever you want.

For people familiar with design patterns, this is essentially an implementation of the “Command” pattern, but with a bit more flexibility in resolving parameters.


This is the dependency injection container that I discussed in a recent post. You register a type with the container, and later can resolve that type to produce an instance. In essence, you tell the container ahead of time the name of the type and specify a list of rules for how to create and initialize an object of that type. Then when we resolve, we get an instance (either new or cached) and execute all the inialization actions to properly initialize that object.

The Rosella::Container type is an implementation of the “Inversion of Control” (IoC) and “Dependency Injection” (DI) principles.


The new Events library allows you to create decoupled events in your application. Early in your program you define a list of events that your program is going to use. Then, you register handlers or listeners who are interested in those events. When the event is raised later in the program, all of the listener Actions are executed to be notified about the event.

This is essentially an implementation of the “Observer/Observable” pattern.


This is a very small library that implements a Prototype system. You register prototype objects with the PrototypeManager. Later in your program when you need an object, you ask the PrototypeManager to clone you a copy of the registered prototype. Think about JavaScript’s object system, and this is essentially that. Notice that Rosella::Container can be used to instantiate prototypes as well, but this library is much thinner and single-purpose than that.

This is an implementation of the “Prototype” pattern.


Borrowed in large part from Kakapo, this is a “mostly” implementation of xUnit-style unit tests. You define a class which is a descendant of Rosella::Testcase, create a suite from it, and then run the suite. Rosella::Testcase and the related machinery automatically finds and executes all test methods in the class and generates all the necessary output. In this case the output is TAP, but the system is extensible enough to allow for other output formats.


This library provides all the necessary logic for implementing a complete, functional TAP harness. By using this library, you can create a fully-functional TAP test harness in about 10 lines of code. It has some pretty nifty features too, which other harnesses in the Parrot ecosystem probably cannot match.

For a bit of perspective, here is an entire test harness implementation using Rosella::Harness:

INIT { pir::load_bytecode("rosella/tap_harness.pbc"); }
my $harness := Rosella::build(Rosella::Harness);
$harness.add_test_dirs("NQP", 't', :recurse(1));
my $output := Rosella::build(Rosella::Harness::Output::Console);

Thats it. Six lines of code and you have a complete TAP harness for your project. Quite powerful, considering how many projects in the Parrot ecosystem have TAP-based test suites.

Future Libraries

There are a few other libraries I am thinking about as well. Here is a quick list of things I am actively planning:

1) proxy: A proxy-building library which can create proxy objects for use in place of other objects for a variety of purposes. 2) mockobject: By using a proxy object to intercept method and vtable calls we can add test logic to create mock object-based testing tools. 3) test: A test library, similar in interface to Perl5’s Test::More. All your favorite functions will be there (ok, nok, is, isnt, diag, etc). The difference is that the output will be configurable just like the xunit test library, and the two will be compatible. You’ll be able to output test results in multiple formats, including but not limited to TAP.

I have a few more ideas in my head, but none as concrete or as thought-out as these. I’ll certainly be making more posts as work progresses on these tools.

So that’s a quick introduction to my new Rosella library. I’m sure I’ll be writing more about it in the days and weeks to come.