Extremely cool. Thanks, GvR.

For my own language design I've wanted to introduce some of this ABC syntax back into Python. Mainly for unpacking data and doing index/slice assignments; a lot of beginners seem to get tripped up because assignments in Python use the same syntax as mutations, so maybe it's better to write e.g. `a['b'] = c` like `set b = c in a`, or `update a with {'b': c}`, or ... who knows, exactly.