[Haskell-cafe] Floating phi, round and even Fibonnaci numbers

[haskell at list.mightyreason.com]

And using dynamic precision :

http://haskell.org/haskellwiki/Applications_and_libraries/Mathematics#Dynamic_precision

The ERA package (darcs get http://darcs.augustsson.net/Darcs/CReal/) one can do 
better...

> import CReal
> 
> even_fibs'' :: (Integral t) => [t]
> even_fibs'' = iterate (\x -> round(fromIntegral x * (dp**3))) 2
>   where dp :: CReal
>         dp = phi
> 
> 
> even_fibs_2 = filter even fibs
>   where fibs = 1 : 1 : zipWith (+) (fibs) (tail fibs)
> 
> z n = take n $ zipWith (\a b -> (a==b,a)) even_fibs'' even_fibs_2
> 
> t z = not $ null $ filter fst $ z
> 
> main = let y = z 1000
>        in putStr . unlines . map show $ y

This works quite well....

(True,2)
(True,8)
(True,34)
(True,144)
(True,610)
(True,2584)
(True,10946)
(True,46368)

...snip...

(True,3987795824799770715342824788687062628452272409956636682999616408)
(True,16892574194241670428824570378554538679120491007541580961500624834)
(True,71558092601766452430641106302905217344934236440122960529002115744)

...