# Difference between revisions of "User:WillNess"

From HaskellWiki

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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 |
where |
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− | g xs = 3 : (gaps 5 $ foldi (\q:qs |
+ | g xs = 3 : (gaps 5 $ foldi (\(q:qs)-> (q:) . union qs) |

[[p*p, p*p+2*p..] | p <- xs]) |
[[p*p, p*p+2*p..] | p <- xs]) |
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## Revision as of 12:59, 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 (\(q:qs)-> (q:) . union qs)
[[p*p, p*p+2*p..] | p <- xs])
fix g = xs where xs = g xs
gaps k s@(x:xs) = if k < x -- | k<=x = minus [k,k+2..] xs
then k : gaps (k+2) s -- inlined to avoid a space leak
else gaps (k+2) xs
```

`foldi`

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