User:WillNess
From HaskellWiki
(Difference between revisions)
m |
|||
| Line 6: | Line 6: | ||
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]) | ||
| + | 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 | + | 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]]. More at [[Prime numbers#Sieve_of_Eratosthenes|Prime numbers]]. | ||
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.
