rPY: Use (r)Python as backend

When designing a Castle-Compiler with a C-backend, we found some nasty details unrelated to CCastle but to the C-language. For example, C has no namespaces (see No Name Collisions); we can simulate them, but that is extra work. Likewise, we need to generate many (data)classes that are very similar. Again, it is possible, but it takes a lot of work: to write the code that generates those almost codes.
Therefore, I started to think about how we can automate that. Or: who has done it before, and what can we borrow?

PyPy –an alternative Python implementation– has developed a concept for that! They have built a translator to convert (r)Python into C and compile that into native machine code.
Can we re-use that? And can it help to realize the “first (bootstrap) compiler” faster?

What is RPython?

RPython is a (restricted) subset of Python. Therefore RPython can be executed in any Python compiler/interpreter, including the typical, standard CPython version, or with PyPy, who invented RPython. They use it to compile their compiler, as one can translate RPython can into native CPU instructions, also

However, RPython is not a Python compiler! Not all Python code can be translated, only a restricted subset.

RPython is not a tool, either. It’s more like a “sub-language”, although the PyPy-teams don’t describe it like that. That language isn’t very strictly defined either: “When a program can be translated (compiled), it’s RPython…” is kind of the rule.

Most relevant is the RPython-toolchain: a (Python) program that will translate a (valid) RPython program into C and then into CPU instructions.

Why RPython?

When a Castle-Compiler emits valid RPython, we can translate that into C and then in native instructions. So we can compile Castle into native instructions!
And, when that extra step results in less development work, it sounds like an interesting idea.

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