DiffArray Performance

[Alastair Reid]

> I haven't checked the DiffArray implementation, though (it would be nice
> if someone could investigate DiffArray and fix any perf problems they
> find).

The most obvious one is that all accesses are protected by an MVar.  Of 
course, this is necessary in some code but I'm guessing that it's almost 
never used in multi-threaded situation.

--
Alastair Reid