# 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 | ||

where | where | ||

− | 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]) | ||

## 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.