Difference between revisions of "User:WillNess"
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g xs = 3 : gaps 5 (foldi (\(c:cs) -> (c:) . union cs) [] |
g xs = 3 : gaps 5 (foldi (\(c:cs) -> (c:) . union cs) [] |
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[[x*x, x*x+2*x..] | x <- xs]) |
[[x*x, x*x+2*x..] | x <- xs]) |
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− | + | gaps k s@(c:t) |
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− | + | | k < c = k : gaps (k+2) s -- == minus [k,k+2..] (c:t), k<=c, |
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− | + | | True = gaps (k+2) t -- fused to avoid a space leak |
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− | fix g = xs where xs = g xs |
+ | fix g = xs where xs = g xs -- global defn to avoid space leak |
</haskell> |
</haskell> |
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Revision as of 06:57, 26 October 2011
I'm 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 xs = 3 : gaps 5 (foldi (\(c:cs) -> (c:) . union cs) []
[[x*x, x*x+2*x..] | x <- xs])
gaps k s@(c:t)
| k < c = k : gaps (k+2) s -- == minus [k,k+2..] (c:t), k<=c,
| 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. union
and more at Prime numbers.
The math formula for Sieve of Eratosthenes,
where
- . . . or, :) :) .
Trial division sieve:
If you're put off by self-referentiality, just replace or on the right-hand side of equations with .