Neil Mitchell wrote:
Hi
Thanks for the tips, Isaac. I fixed my Ord decl. Too bad about the
run-time time & space overhead. I guess that's not fixable. Perhaps Simon
will decide to follow Pepe's suggestion of liberal deriving when
UndecidableInstances enabled.
If you implement compare, isn't everything else simply a small
constant over compare? And thats only if the optimiser doesn't pick up
that constant and throw it away.
In general, I think if you implement compare in Ord, you are likely to
end up with best (or very near best) performance.
It'll probably only be a significant difference if (f a) or (g a) has an
unusual Ord instance that has rather different implementations of the
different members (<), (compare) etc. Which probably never actually
happens.
Implementing compare likely needs to make one more comparison somewhere,
versus (<) etc. (unless the optimizer is really good). Usually compare
is the nicest anyway.
Isaac
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