[Haskell-cafe] Vedr: Are storable-mutable-vectors in two dimensions possible in Haskell?

Fixie Fixie fixie.fixie at rocketmail.com
Sat Dec 1 12:34:21 CET 2012


Sounds good. I thought something like this could be the solution.

But it might be that my type-knowledge is not good enough - but I have not been able to do this. Example:

vec1 <- MV.new 1000 :: IO (V.MVector (PrimState IO) Int)



Data.Vector.singleton vec1 -- does not work, gives a lot of type-errs.

Felix



________________________________
 Fra: Dmitry Dzhus <dima at dzhus.org>
Til: Fixie Fixie <fixie.fixie at rocketmail.com>; Haskell cafe <haskell-cafe at haskell.org> 
Sendt: Lørdag, 1. desember 2012 12.27
Emne: Re: [Haskell-cafe] Are storable-mutable-vectors in two dimensions possible in Haskell?
 
01.12.2012, 15:14, "Fixie Fixie" <fixie.fixie at rocketmail.com>:
> Hello haskellers
> I am struggling with this package: Data.Vector.Storable.Mutable
> I am creating vectors like this: MV.new 1000 :: IO (V.MVector (PrimState IO) Int)
> Now I would like access to this vectors in linear time, like I could have done in C using pointers.
> The problem is that I do not know which datastructure to keep my vectors in. If I put them in a list, the access is very slow. Even a binary tree is very slow compared to a C-version.
> I have tried to make an array og vector of storable-mutable vectors, but have not manged to accomplish this - even though there must be a haskell way :-)

You can use boxed vector as a first-level structure holding pointers
you your storable vectors to perform O(1) indexing on first dimension.

Alternatively, if your matrix is dense, store your data in a
one-dimensional vector and use Repa as a thin wrapper to perform
multi-dimensional indexing (see toIndex/fromIndex
Data.Array.Repa.Shape).
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