For anyone who's interested, I've written up a (highly experimental!) immutable
string data type
`here<https://gist.github.com/Varriount/fd56b757c6de57ab9712>`_.
The data type roughly follows the semantics of Python's ``string`` data type,
with the exception that it appears mutable (eg, the '&=' operator is
supported). Please note that slice and substring operations still make copies -
I couldn't implement non-copying behavior and still maintain implementation
simplicity.
