[Haskell-cafe] Construction of short vectors

[Alexey Khudyakov]

On Fri, 25 Jun 2010 18:30:06 -0300
Felipe Lessa <felipe.lessa at gmail.com> wrote:

> On Fri, Jun 25, 2010 at 12:41:48AM +0400, Alexey Khudyakov wrote:
> > Then constructor like one below arise naturally. And I don't know how to write
> > them properly. It's possible to use fromList but then list could be allocated
> > which is obviously wasteful.
> 
> Did you see the generated core?  I think you should give a try to
> the following simple code:
> 
>   import qualified Data.Vector.Generic as VG -- vector == 0.6.*
> 
>   vector2 :: Double -> Double -> Vec2D
>   vector2 x y = Vec2D (VG.fromListN 2 [x,y])
> 
I tryed to look at ghc core output but it was totally incomprehensible.
Is there any documentation about how to inspect and interpret generated
code, good practices etc?

> > Another question is there any specific problems with short vectors? They could
> > be just 2 elements long. I mean performance problems
> 
> Probably there will be more overhead than defining
> 
>   data Vec2D = Vec2D {-# UNPACK #-} !Double
>                      {-# UNPACK #-} !Double
> 
> You should profile to see how much difference there is between
> those representations.
> 
Sure. This price of code generality.