[Haskell-cafe] Code Golf

[MigMit]

If I understand the problem correctly...

Prelude> let diag = concat . diags where diags ((x:xs):xss) = [x] : zipWith (:) xs (diags xss)
Prelude> take 10 $ diag [[ (m,n) | n <- [1..]] | m <- [1..]]
[(1,1),(1,2),(2,1),(1,3),(2,2),(3,1),(1,4),(2,3),(3,2),(4,1)]

Sebastian Fischer wrote on 15.04.2009 14:32:
> Fancy some Codegolf?
> 
> I wrote the following function for list diagonalization:
> 
>  > diag l = foldr (.) id ((sel l . flip sel) ((:[]).(:))) []
>  >  where
>  >   sel = foldr (\a b c -> id : mrg (a c) (b c)) (const []) . map (flip 
> id)
>  >
>  >   mrg []     ys     = ys
>  >   mrg xs     []     = xs
>  >   mrg (x:xs) (y:ys) = (x.y) : mrg xs ys
> 
> Self explanatory, isn't it? Here is a test case:
> 
>     *Main> take 10 $ diag [[ (m,n) | n <- [1..]] | m <- [1..]]
>     [(1,1),(1,2),(2,1),(1,3),(2,2),(3,1),(1,4),(2,3),(3,2),(4,1)]
> 
> I was trying to golf it down [^1] but my brain explodes. If you succeed 
> in reducing keystrokes, I'd be happy to know!
> 
> Cheers,
> Sebastian
> 
> [^1]: http://codegolf.com/
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