Performance horrors

John Meacham john at
Tue Aug 26 19:00:38 EDT 2008

nub has a couple advantages over the n log n version, the main one being
that it only requires an 'Eq' constraint, not an 'Ord' one. another
being that it is fully lazy, it produces results even for an infinite
list. a third is that the results come out in the order they went in.

That said, I have a 'snub' (sorted nub) routine I use pretty commonly as
well defined in the standard way. If you have something like

setnub xs = f Set.empty xs where
        f _ [] = []
        f s (x:xs) = if x `Set.member` s then f s xs else f (Set.insert
x xs) (x:xs)

then you can use 'RULES' pragmas to replace nub with setnub when it is

Though, I have reservations about using RULES to change the order of


John Meacham - ⑆⑆john⑈

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