Joe asks for clarification.
Currently, the report says nothing about whether an instance
of Ix should perform bounds checking, or whether this is done
automatically by the implementation.
My proposal was to say that it should be in the instance
declaration, which gives the user a variety of options as to
how to implement bounds checking, including not at all.
The alternative is to say that the implementation itself
will perform a bounds check, which constrains the implementation
but guarantees that it always happens.
On pondering this after Joe's question, I find I don't have
a strong feeling in either direction. But we ought to specify
which (so that a careful programmer knows whether to include
bounds checks, or whether the system will provide).
Cheers, -- P
