DiffArray Performance

[MR K P SCHUPKE]

>never used in multi-threaded situation.

Erm, nearly all my code in Haskell is multi-threaded. One of the 
main reasons why I am using haskell is the low-cost light weight
multi-threading. Surely this is a big win for Haskell on SMP/Numa
machines - which are surely the future - as even Intel have realised
they can't just keep ramping up clock speeds and have gone multi-core
for their next pentium iteration. Just look at the benchmarks for the
multi-cpu opteron machines!

I would hesitate to make any type unsafe for multi-threading by default - I
think all the guards should be in as standard ... maybe a compile time
(or run-time) flag to replace the guards with NO-OPS for single CPU
machines might be a sensible option.

	Regards,
	Keean Schupke.