G'day all. Adrian Hey wrote:
This might be a reasonable thing to say about *sortBy*, but not sort as the ordering of equal elements should not be observable (for any correct instance of Ord). It should be impossible to implement a function which can discriminate between [a,a],[a,b],[b,a],[b,b] if compare a b = EQ.
Nonsense. Consider a Schwartzian transform wrapper:
data OrdWrap k v = OrdWrap k v
instance (Ord k) => Ord (OrdWrap k v) where
compare (OrdWrap k1 v1) (OrdWrap k2 v2) = OrdWrap k1 k2
It would be incorrect (and not sane) for sort [a,b] to return [a,a] in
this case, though a case could be made that either [a,b] or [b,a] make
sense.
Quoting Jules Bean
Stability is a nice property. I don't understand why you are arguing against this so aggressiviely.
Stability is an occasionally very useful property. However, if there is a tradeoff between stability and performance, I'd prefer it if the library didn't choose for me. Cheers, Andrew Bromage