[Haskell-cafe] Progress on shootout entries

[Chris Kuklewicz]

Could you post your code to this mailing list or to the wiki at
http://haskell.org/hawiki/FannkuchEntry ?

Bertram Felgenhauer wrote:
>>And for sanity's sake, I wish one of the entries would have documentated
>>a clear way to understand the permutation generator.   The PHP and Lua
>>versions are almost legible.
> 
> 
> Here's a neat Haskell version:
> 
> -- rotate initial n elements of the list left by one place
> rotate n (x:xs) = rot' n xs where
>     rot' 1 xs     = x:xs
>     rot' n (x:xs) = x:rot' (n-1) xs
> 
> permutations l = foldr perm' [l] [2..length l] where
>     perm' n l = l >>= take n . iterate (rotate n)
> 
> Combined with Jan-Willem Maessen's ideas (i.e. the single-pass flop)
> this runs about 85 times faster than the current shootout entry.
> 
> Bertram
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