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User:WillNess

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Revision as of 13:38, 7 August 2011 by WillNess (Talk | contribs)

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I am a newbie, interested in Haskell.

I like this:

primes = 2 : g (fix g) -- double staged production idea due to M. O'Neill
  where
    g xs = 3 : (gaps 5 $ foldi (\(q:qs) -> (q:) . union qs)
                               [[p*p, p*p+2*p..] | p <- xs])
    gaps k s@(x:xs)                
       | k < x = k : gaps (k+2) s     -- | k<=x = minus [k,k+2..] xs
       | True  =     gaps (k+2) xs    -- inlined to avoid a space leak
 
fix g = xs where xs = g xs            -- global defn to avoid space leak

foldi is on Tree-like folds. More at Prime numbers.