ANNOUNCE: yap-0.0 - yet another prelude

[Henning Thielemann]

On Wed, 10 Aug 2011, Paterson, Ross wrote:

> Yet another restructuring of the Prelude numeric classes on algebraic lines, proposed for a revision of the Haskell Prelude:
>
> http://hackage.haskell.org/package/yap-0.0

A nice lightweight design, both in terms of the use of type extensions and 
import dependencies, that should people encourage to use it, when they are 
afraid of changing to a more radical approach like numeric-prelude. I 
would have prefered the name AdditiveGroup to AbelianGroup, since with '+' 
and '-' and '0' I associate more than just the laws of an Abelian group. 
The multiplicative group of rational numbers is abelian, too.

  I also like the Quantity datatype. It can be used with any framework for 
type-encoded physical units. I have for instance a Haskell98 approach, 
that could be sepearated from numeric-prelude:
   http://hackage.haskell.org/packages/archive/numeric-prelude/0.2.2/doc/html/Algebra-DimensionTerm.html
  In this approach I encode composed units using type constructors like Mul 
and Div and the user is responsible for showing that (Mul a b) is 
equivalent to (Mul b a). Sure, its cumbersome, but Haskell 98 and I hope 
you do not need those proofs very often.