# Difference between revisions of "User:WillNess"

From HaskellWiki

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I am a newbie, interested in Haskell. |
I am a newbie, interested in Haskell. |
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− | I like ''this'': |
+ | I like ''[http://ideone.com/qpnqe this]'': |

<haskell> |
<haskell> |
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− | primes = 2 : 3 : ([5,7..] `minus` |
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+ | primes = 2 : g (fix g) -- double staged production idea due to M. O'Neill |
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⚫ | |||

+ | fix g = xs where xs = g 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 18:06, 3 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
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.