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User:WillNess

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<code>foldi</code> is on [[Fold#Tree-like_folds|Tree-like folds]] page. More at [[Prime numbers#Sieve_of_Eratosthenes|Prime numbers]].
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<code>foldi</code> is on [[Fold#Tree-like_folds|Tree-like folds]] page. <code>union</code> and more at [[Prime numbers#Sieve_of_Eratosthenes|Prime numbers]].

Revision as of 07:47, 8 August 2011

I am a newbie, interested in Haskell.

I like this: 

--   inifinte folding idea due to Richard Bird
--   double staged production idea due to Melissa O'Neill
--   tree folding idea Dave Bayer / simplified formulation Will Ness
primes = 2 : g (fix g) 
  where                
    g ps = 3 : gaps 5 (foldi (\(q:qs) -> (q:) . union qs) 
                             [[p*p, p*p+2*p..] | p <- ps])
    gaps k s@(c:t)                
       | k < c = k : gaps (k+2) s     -- | k<=c = minus [k,k+2..] s
       | True  =     gaps (k+2) t     --   fused to avoid a space leak
 
fix g = xs where xs = g xs            -- global defn to avoid space leak

foldi is on Tree-like folds page. union and more at Prime numbers.

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