[Haskell-cafe] Fwd: Fwd: Re: the state of Yarr?

Dominic Steinitz dominic at steinitz.org
Wed Jan 6 09:48:59 UTC 2016

A problem with my email prevented this making it on to the mailing list.

Hi Petr,

I am not actively developing Yarr but I would very much like to. I keep
it from bit-rotting. The problem as always is finding time. On the other
hand I don't think repa is very active e.g. upgrading to vector-0.11
took a while to happen although clearly more active than me on Yarr!

What I'd like is something like Python's numpy but safer and faster. If
you look at the static module in the hmatrix package
you can see how type level literals can be used to prevent e.g.
multiplying two inconsistent matrices together at compile time. I am
sure we could do something better with either Yarr or repa (repa will
currently give out of bounds errors at runtime).

For reasons I don't understand (I think a bug in Haddock) the
documentation does not get generated.

There are examples of its use here:
https://github.com/leventov/yarr/tree/master/tests. I wrote a blog using
repa and Yarr here:
and compare performance. You can safely ignore the theory and need only
look at "Repa Implementation", "Yarr Implementation" and "Performance".

I think performance will depend on your application. I believe (but
haven't confirmed) that repa will outperform Yarr on e.g grid based
problems such as numerical methods for diffusions and Poisson. In the
case of planets (or stars or particles) where everything is influenced
by everything else then repa is a bad fit and Yarr outperforms.

If your application is linear algebra, I would think that hmatrix would
have what you want or could be extended to give what you want since it
is LAPACK under the covers.

I am very excited that you are interested in this area; it often feels
very lonely.

Best wishes, Dominic.

On 06/01/2016 09:10, Petr Pudlák wrote:
> Hi Dominic,
> what is the current state of Yarr? Is it being actively developed? Is
> there some tutorial or documentation available?
> I'm deciding between repa and yarr for some linear algebra
> computations. I found some references that yarr is more performant,
> but I couldn't find much documentation and the hackage page [1] hasn't
> indexed most modules for some reason, so there seems to be no good
> place to start from. And the last commit was 9 months ago.
> [1]https://hackage.haskell.org/package/yarr
> Thank you,
> Petr

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