Next, when the body of a progn is expanded as part of the arc compilation process, the 'curly token is checked for and replaced with a let.
This means you can also write the following:
(do (curly (+ 1 2))
(cons ^ ^))
Also, since this feature hijacks some valuable characters, it would need to be applicable for far more situations than just 'do, or it would be a waste. I believe it fulfills this requirement.