On 10/22/07, Tim Docker <[EMAIL PROTECTED]> wrote: > TJ: > > > After all, sometimes all you need to know about a list is that > > all the elements support a common set of operations. If I'm > > implementing a 3d renderer for example, I'd like to have > > > > class Renderable a where > > render :: a -> RasterImage > > > > scene :: Renderable a => [a] > > > Everyone has launched into explanations of how to use existentials > to do this, but you may be happy in just haskell 98. In the above, > you could just have: > > scene :: [RasterImage] > > Laziness will ensure that the computation/storage of the images > will not occur until they are used. > > Tim >
Ah... indeed it can, in this case. It won't work if class Renderable also has a method for saving to file, etc, I suppose, unless scene :: [(RasterImage,IO (),...whatever other operations...)] Thanks for the heads up :) TJ _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
