Haskell Platform proposal: Add the vector package

[Henning Thielemann]

On Mon, 18 Jun 2012, Roman Leshchinskiy wrote:

> There are type families, rank-n types, unboxed types and other goodies 
> deep in the guts of vector so the Storable part is very much 
> GHC-specific. To be honest, I don't think being portable is feasible for 
> high-performance code at the moment, the language standard simply 
> doesn't have enough tools for this. Which is a shame, really.

I am not mainly interested in the efficient implementation. I am 
completely ok with having the definition of (Vector a) in a separate 
package, such that it can be used by vector (GHC only) and storablevector 
(portable).

However, I have just looked into Vector.Storable and it looks like

   data Vector a = Vector Int (ForeignPtr a)

I thought it was

   data Vector a = Vector {len :: Int, allocated :: ForeignPtr a, start :: Ptr a}

ByteString looks like:

   data ByteString = PS {allocated :: ForeignPtr Word8, start, length :: Int}

Both forms allow efficient slicing.
How do you perform efficient 'take' and 'drop' ?


> FWIW, Storable vectors are fundamentally broken, anyway, since a 
> Storable instance can perform arbitrary I/O in its methods but a pure 
> vector based on Storable will necessarily have to unsafePerformIO these 
> operations.

That's unfortunately true.

> Storable should *really* live in ST but it's too late for that now.

How would this prevent from broken pointer arithmetic?