...at the REPL, you'd better be careful not to give "a" a value, or it'll break your code. I think the cognitive overhead of worrying about that far outweighs the cost of using the ' operator.
Thank you so much for saying that. XD All of it. I feel the same way, but I can't help but think I'm just out of my element and resistant to change. Managing a single character here or there isn't a trivial problem, but I personally don't care much either way as long as I can also manage my code well on a large scale. Good to know I'm not the only one.
...warn when assigning to an already-bound variable...
I'm too much a fan of extensibility (where redefining things is normal) and of namespaces (where neglectable names are already protected from conflict) for 'safeset to seem like a positive thing, but in this case, it could just be me. ^^