The other day I quietly bumped the Rosella Template library to stable status. I’ve been living with the API for a while and am happy with it for the most part. I’ve also gotten documentation and unit tests up to a nice level and I felt pretty comfortable that it wasn’t a buggy, incomplete piece of crap. I don’t want to claim that it’s perfect, but I’m pretty happy with it as a first attempt. There are a few internal bits that are awkward and difficult to test, but the overall public-facing form of the library is working well enough.

It’s extremely easy to write up things like unit tests and documentation when I have a templating tool that can produce files for those kinds of things semi-automatically.

I’ve talked a lot about the templating library in two previous posts, and am planning a separate post for it later this week, so I won’t go into details about it here as well. As I start putting together more tools that use it, I’ll show those off so the reader can see the new library in action.

Instead, today I want to talk about some of the new Rosella libraries I have been playing around with. Some or all of these might become a stable part of Rosella some day too, but right now they aren’t quite ready for prime time.


Rosella.Assert, formerly known as “Contract” is a library for debugging. It provides a few interesting tools: Runtime assertions, debug logging, and contracts. All of these features read a global flag to determine if they are on or off. If off, calls to the various assert, debug, and contract routines all do nothing. The calls themselves aren’t completely removed, but they do short-circuit and exit early with no side-effects. Several people, especially GSoC students have asked for these kinds of debugging routines, so it’s about time somebody added them.

The library basically does nothing unless you turn it on, so it won’t interfere with your code at all unless you enable it. To turn on the Assert library, you do this:


Without that line of code, most calls in the Assert library do nothing at all. The calls are still made, however, but they check the flag and immediately return if it’s not activated. Winxed does do dead code elimination from conditionals with constant expressions. That dead-code elimination along with a new __DEBUG__ constant NotFound added recently, means that you can make assertions disappear entirely if you want:

if (__DEBUG__)
    var(Rosella.Assert.debug)("This message probably won't appear");

The Assert library provides assertions too. So you can start peppering your code with calls to the assert function:

using Rosella.Assert.assert;
assert(1 == 1);

Notice that the conditional here is executed before the assert function is called, so side-effects aren’t invisible. However, a different form of assertion takes a predicate Sub, which won’t be evaluated at all if the library is turned off:

using Rosella.Assert.assert_func;
assert_func(function() { return 1 == 1; });

It’s not very pretty, but it does what you expect it to do. If the Assert library is enabled and the assertion condition fails, an error message and backtrace are printed. Otherwise, nothing happens. Likewise, you can make the code disappear entirely using the __DEBUG__ flag.

The new library also provides contracts in two flavors: Object interface contracts, and function contracts. In the first, we verify certain features of an object: Does it have the necessary list of methods? Does it have the necessary attributes? We can use the contract to verify that the object has the expected interface, or throw an assertion failure if not. In the second type, we can insert predicates into an existing function or method, to do pre- and post-call testing of values. For instance, to assert that the first argument of a call to method bar() on class Foo is never null, we can set up this assertion:

var c = new Rosella.Assert.MethodContract(class Foo);
c.arg_not_null("bar", 0);

likewise, to verify that the method bar() never returns a null value, we can do the following:

c.return_not_null("bar", 0);

That will automatically inject predicates into the method, which will be checked every time the method is invoked, if the Assert library is enabled. If a check fails, you get an exception and a backtrace. If you turn off the library, no checking happens and method calls happen like normal with no interference or slowdown.

One last detail, the Assert library integrates with the Test library, if you have them both loaded together. If you use Assert in a test suite using Rosella Test, you can use assertions and contracts as tests directly, and things printed out with debug() are printed out as normal TAP diagnostics. It’s quite handy indeed, because if you have put the assertions and contracts into your code, you now have test code running inside your program, testing things that would otherwise be hard to get to. Setting up predicate assertions on methods in your code is a handy and useful replacement for mock objects, if mocks aren’t your kind of thing.

This library has a lot of potential to be used as a debugging and testing aide, and I expect to be using it a lot in my own work once I get some of the last details sorted out.


Rosella.Reflect is a library for doing easy, familiar reflection. Basically, it’s an abstraction over methods and tools already provided by Parrot’s built-in types, but with a nicer interface. It is the same motivation as I had for the FileSystem library, which is like a much nicer veneer over the OS PMC and a handful of other lower-level file-manipulation details provided by Parrot. Right now Reflect is an early-stage plaything, but it’s already looking nice and I have plenty more things to add to it.

With Rosella.Reflect, you can do things like this:

var f = new Foo();
var c = new Rosella.Reflect.Class(class Foo);
var b = c.get_attribute("bar");
b.set_value(f, "hello");        # Set = "hello"
var m = c.get_method("baz");
m.invoke(f, 1, 2, 3)            # f.baz(1, 2, 3)
var x = new Bar();
m.invoke(x, 1, 2, 3)            # Error, x is not a Foo

Basically, it provides type-safe object wrappers for classes, attributes and methods. It provides routines for iterating attributes and methods, dealing with the indirectly, and doing other reflection-based tasks too.

In the future I want to add tools for building classes at runtime, tools for exploring packfiles, namespaces, and lexicals, and doing a few other things. This library is pretty heavily influenced by some of the things Parrot user Eclesia has been doing with his Eria project. It gives a nice object-based way to interact with some things in Parrot that don’t always have the most friendly interfaces.

This library is very very young and is mostly a prototype. I am looking for more things to add to it, and hope it will become more generally useful. It’s complicated by the fact that the upcoming 6model refactors could radically change the way we do some types of reflection, so I don’t want to reinvent any wheels.


Rosella.Dumper is a replacement for the Data::Dumper library that ships with Parrot. It uses an OO interface with pluggable visitors and configurable settings. It’s very early in development but it’s already much more functional and usable than Data::Dumper. With the new interface, you can do something like this:

var dumper = new Rosella.Dumper();
string txt = dumper.dump(obj);

The Dumper object contains several collections of DumpHandler objects, which are responsible for dumping out particular types of object. DumpHandlers are arranged into 4 groups: type-based dumpers that dump objects of specific types, role-based dumpers which dump objects that implement a given role, miscellaneous dumpers which are given the opportunity to dump anything else, and special dumpers for things like null and anything that falls through the cracks. By mixing and matching the kinds of things you want to see dumped, you can customize behavior. By subclassing the various bits, you can change behavior and output formatting.

This library is pretty straight forward, and is already pretty generally useful. I have a few decisions left to make about the API and some of the default settings, but it’s useful and usable now and I’ve already employed it myself for several recent debugging tasks.


This is the newest prototype library of all. So new that as of the publishing of this blog post I haven’t pushed the code to github yet. Rosella.CommandLine is a library for working with the command line and command line arguments in particular. Basically, it’s a replacement for the GetOpt::Obj library which comes with Parrot, along with a few other features for making program entry easier. To give a short example, here’s a test program I’ve been playing with using the new library:

function main[main](var args) {
    var rosella = load_packfile("rosella/core.pbc");
    var program = new Rosella.CommandLine.Program(args);;

function real_main(var opts, var args, var other) {

The main function initializes Rosella and loads in the CommandLine library. Then it creates a Rosella.CommandLine.Program object, to handle the rest of the details. The Program object takes the program arguments and automatically parses them out into a hash and some arrays based on some basic syntax rules. You can specify formats like you do in GetOpt::Obj if you want, or the library can parse them by default rules and just pass you the results. The run method of the Program object takes a reference to a Sub object to treat like the start of your program. It sets up a try/catch block to do automatic error catching and backtrace printing. Also, it can be used to dispatch certain arguments to different routines entirely, which is useful if you need to set up routines for printing out help or version information:, {
    "help" => function() { ... },
    "version => function() { ... }

The argument processing is done by a new Rosella.CommandLine.Arguments class, which mimics much of the behavior of GetOpt::Obj, but has a few subtle differences, which are partly because it’s early in the implementation and partly because I like certain syntaxes better than others. Also, if you return an integer from your real_main routine, that integer will be the exit code of the process, which should be familiar for most C coders and their ilk. If you return no value, or if you use the exit opcode, things will continue to behave as you would expect. As with all Rosella libraries, there will be plenty of opportunity for subclassing and customization, so if you need something different from the provided defaults, it will be easy to change things.

I have a couple other projects in mind that I want to start playing with, some in Rosella, and some that intend to use Rosella to build bigger things. I’ll certainly share more information about whatever else I am planning in future blog posts.