# User:WillNess

### From HaskellWiki

(Difference between revisions)

Line 4: | Line 4: | ||

<haskell> | <haskell> | ||

− | + | -- inifinte folding idea due to Richard Bird | |

− | where | + | -- double staged production idea due to Melissa O'Neill |

− | g | + | -- tree folding idea Dave Bayer / simplified formulation Will Ness |

− | + | primes = 2 : g (fix g) | |

− | gaps k s@( | + | where |

− | | k < | + | g ps = 3 : gaps 5 (foldi (\(q:qs) -> (q:) . union qs) |

− | | True = gaps (k+2) | + | [[p*p, p*p+2*p..] | p <- ps]) |

+ | gaps k s@(c:t) | ||

+ | | k < c = k : gaps (k+2) s -- | k<=c = minus [k,k+2..] s | ||

+ | | True = gaps (k+2) t -- fused to avoid a space leak | ||

fix g = xs where xs = g xs -- global defn to avoid space leak | fix g = xs where xs = g xs -- global defn to avoid space leak | ||

</haskell> | </haskell> | ||

− | <code>foldi</code> is on [[Fold#Tree-like_folds|Tree-like folds]]. More at [[Prime numbers#Sieve_of_Eratosthenes|Prime numbers]]. | + | <code>foldi</code> is on [[Fold#Tree-like_folds|Tree-like folds]] page. More at [[Prime numbers#Sieve_of_Eratosthenes|Prime numbers]]. |

## Revision as of 15:25, 7 August 2011

I am a newbie, interested in Haskell.

I like *this*:

-- inifinte folding idea due to Richard Bird -- double staged production idea due to Melissa O'Neill -- tree folding idea Dave Bayer / simplified formulation Will Ness primes = 2 : g (fix g) where g ps = 3 : gaps 5 (foldi (\(q:qs) -> (q:) . union qs) [[p*p, p*p+2*p..] | p <- ps]) gaps k s@(c:t) | k < c = k : gaps (k+2) s -- | k<=c = minus [k,k+2..] s | True = gaps (k+2) t -- fused to avoid a space leak fix g = xs where xs = g xs -- global defn to avoid space leak

`foldi`

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