1+2. And objects!

Finally done with exams, yesterday was my last. Ever, hopefully. So I had time to do some work. You can find it at either http://bitbucket.org/lucian1900/puffin or http://github.com/lucian1900/puffin. I pull from bitbucket, but push to both.

At the moment I am focused entirely on correctness and completeness. I care little about interop with other parrot languages and not at all about performance. I don't want to waste time on issues that don't have established solutions on parrot anyway. Instead, I want a correct python implementation on parrot. Interop and performance can be fixed later.

I started writing a compiler using python3's ast module, generating PIR. I focused on a subset of python that supports int literals, int addition, assignment and printing. I wrote some tests, to check both the PIR output and its execution. This was straightforward, the ast module is very good.

Python's semantics are almost entirely defined by its object system, so I decided to start implementing it. I looked at whiteknight and NotFound's experiments with prototype objects (found in rosella/unstable/prototype). I found it unsuitable to directly support Python's object system, but that it could be a useful source of inspiration.

I don't want to write assembly and I have almost no experience with Perl, so I decided to use Winxed to implement an object system, on top of Object/Class. Objects are backed by a Hash, for __dict__, which contains all attributes of the object. Both types (classes) and objects (instances) are instances of 'instance', a parrot Class. 'type' inherits from 'instance', since types are also objects in python.

Python objects can be interracted with from Winxed/PIR similarly to how CPython does: "foo.bar" becomes "foo.__class__.__dict__['__getattribute__'](foo, 'bar')".
The object system boostraps itself to the point where there is a significant subset of builtins, with almost entirely correct pythonic behaviour: type, object, int, tuple, function, BaseException etc. From there on, in theory, everything can be implemented in pure python.

The compiler doesn't yet generate code for this object system, since there are a few vital bits missing, such as correctly working methods and metaclasses. Also, I have few tests for the object system, I'd like concentrate on improving that situation.

I had initially also considered 6model, but its unfortunate lack of documentation prevented me from properly evaluating it. After some chats with jnthn and his recent (very useful) docs, I have a much better understanding of 6model, it is in fact quite similar to my object system (but more general). Since Python's interaction with its objects follows a very clearly defined interface, I believe it'll be very easy to rewrite the object system from under the compiler, using whatever ends up being the recommended method. Since I've already built much of what 6model would offer me, I'll stick with this (I know, it's a bit NIH) until 6model gets integrated into parrot better.

Another issue is building&packaging. Packaging for Python(3) is well established, and Parrot has its own distutils. However, since I have code in both Python and a parrot language, the interraction is a bit tricky. The same goes for testing, in fact. I see two possible solutions: 1) write build scripts in python/distutils for building winxed&pir, likely based on allison's work in pynie/setup.py or 2) write setup.py for python code and setup.winxed for parrot code, and add a command to setup.py that calls setup.winxed. I'm inclined to prefer the second option.

After I've tested the builtins in my object system, I'll start targeting the compiler to use them. Afterwards, I'll look at supporting more 'exotic' features, such as I/O module importing.