Strings should not be primitive values

[erjiang]

Strings should not be primitive values

[yhara]

Yes, they should be mutable. But do you really need it?
string-set! implemented with immutable JavaScript strings may not be so fast.

[erjiang]

I opened this issue merely because I was concerned for the semantics of strings and also for convenience for the user who might want to use string-set!. Speed obviously won't be good, but that could be an implementation note. It's halfway done in https://github.com/erjiang/biwascheme/tree/string-obj if you're interested.