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User:WillNess

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Revision as of 18:06, 3 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
fix g = xs where xs = g xs
g xs = 3 : (gaps 5 $ foldi (\x:xs -> (x:) . union xs)
                           [[p*p, p*p+2*p..] | p <- xs])
gaps k s@(x:xs) -- | k<=x = minus [k,k+2..] xs
                -- inlined to avoid a space leak
     = if k < x 
         then k : gaps (k+2) s 
         else     gaps (k+2) xs

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