I agree that I think that this `__tt_map` is a weakness behind this approach. It would be a little nice to have a vague idea of how to move away from this before landing, but I think that having this for now is totally fine in the meantime.

Would it be possible to give our new loadable syntax extensions a run for their money here? I came up with a few ideas to move away from `__tt_map`, but this really does seem like a clean solution, we just don't want it defined in the compiler.

Basically, I think we should open an issue on converting this to a true syntax extension. This will have a number of bootstrapping issues, but once we iron them out we can remove the `__tt_map` feature from the compiler (hurray!)