User:WillNess
From HaskellWiki
(Difference between revisions)
| Line 5: | Line 5: | ||
<haskell> | <haskell> | ||
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 | ||
| + | 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 | ||
| + | |||
fix g = xs where xs = g xs | fix g = xs where xs = g xs | ||
| - | |||
| - | |||
| - | |||
| - | |||
| - | |||
| - | |||
| - | |||
</haskell> | </haskell> | ||
<code>foldi</code> is on [[Fold#Tree-like_folds|Tree-like folds]]. More at [[Prime numbers]]. | <code>foldi</code> is on [[Fold#Tree-like_folds|Tree-like folds]]. More at [[Prime numbers]]. | ||
Revision as of 07:53, 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 (\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 fix g = xs where xs = g xs
foldi is on Tree-like folds. More at Prime numbers.
