[Haskell-cafe] How to write fast for loops

[John Lato]

On Apr 27, 2014 1:10 PM, "Niklas Hambüchen" <mail at nh2.me> wrote:
>
> On 27/04/14 03:28, John Lato wrote:
> > No, I mean this:
> >
> >> V.forM_ (V.enumFromN 1 n)
>
> Hey John,
>
> unfortunately that's not fast, and it eats all the RAMs.
>
> Here comes the sad comparison of looping in Haskell:
>
> - loop (maxBound :: Word32)
>   3 seconds, constant space
>
> - forM_ [0..maxBound :: Word32]
>   36 seconds, constant space
>
> - V.forM_ (V.enumFromTo 0 (maxBound :: Word32))
>   37 seconds, constant space
>
> - V.forM_ (V.enumFromN 0 (fromIntegral (maxBound :: Word32)))
>   linear space -> crashes
>
> All loops execute `return ()`.

Hmm.  Are you using regular vectors or unboxed? Also what sort of crash? Is
it a stack space overflow or are you on a 32-bit platform?
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