# User:WillNess

### From HaskellWiki

(Difference between revisions)

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

fix g = xs where xs = g xs |
fix g = xs where xs = g xs |
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− | g xs = 3 : (gaps 5 $ foldi (\x:xs -> (x:) . union xs) |
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− | [[p*p, p*p+2*p..] | p <- xs]) |
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− | gaps k s@(x:xs) -- | k<=x = minus [k,k+2..] xs |
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− | -- inlined to avoid a space leak |
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− | = if k < x |
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− | then k : gaps (k+2) s |
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− | else gaps (k+2) xs |
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</haskell> |
</haskell> |
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## Revision as of 07:53, 7 August 2011

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 (\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 fix g = xs where xs = g xs

`foldi`

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