# 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)-> (q:) . union 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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+ | gaps k s@(x:xs) |
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+ | | k < x = k : gaps (k+2) s -- | k<=x = minus [k,k+2..] xs |
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+ | | True = gaps (k+2) xs -- inlined to avoid a space leak |
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− | fix g = xs where xs = g xs |
+ | fix g = xs where xs = g xs -- global defn to avoid space leak |

− | |||

− | gaps k s@(x:xs) = if k < x -- | k<=x = minus [k,k+2..] xs |
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− | then k : gaps (k+2) s -- inlined to avoid a space leak |
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− | else gaps (k+2) xs |
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</haskell> |
</haskell> |
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## Revision as of 13:38, 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])
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.