Making immutable instances

[Paul Rubin]

Mike Meyer <mwm at mired.org> writes:
> Lots of people seem to want immutable instances. Nobody seems to have
> a use case for them.

What is the use case for immutable strings?  Why shouldn't strings be
mutable like they are in Scheme?

Generally if I know I don't plan to mutate something, I'd want to make
it immutable so the runtime system can notice if I make an error.
It's like an "assert" statement spread through the whole program.