Durst progress

My new language is moving along slowly but steadily. The parser is now complete, and though I am tempted to rewrite it after reading about Marpa parsing, this would probably be counter-productive. Adding an interpreter was fairly simple, but this is running on an expression AST, not any sort of CFG.

The current plan is to first extend the language with functions, including some basic IO, then move on to compilation. Compilation will be done by first converting to an SSA CFG similar that that of LLVM, then converting to LLVM and letting it do the hard work of actually producing machine code.

Coming up with a good representation for the CFG is a bit difficult, because I want to have want operation to point to its operands, but naively done this is impossible in Rust, which forbids cycles of pointers. As such, I plan to create an (internally unsafe) module for a CFG using raw pointers, and use that.

Once I have basic compilation working, the plan is to play around with optimization by creating a framework similar to Hoopl. I have a number of ideas of how to improve upon that work, including interleaving the backwards and forwards passes and immediately applying transformations that are known to be valid.