The Haskell 1.3 effort is nearly complete. Although a new report is not yet complete, all proposed changes to the language as well as the new Prelude are now available for public comment. These documents are available on the web at http://www.cs.yale.edu/HTML/YALE/CS/haskell/haskell13.html
Your error messages from ghc are correct: you have violated the infamous C-T rule (section 4.3.2, page 32) which restricts instance declarations to the module containing either the class or the datatype. Since (,) and Num are both in the prelude, you can't compile this in official Haskell 1.2.
Ignoring the issue of whether the current Prelude would be improved using a more general class heirarchy, let me point out the real failing of Haskell here. The problem is not so much that the prelude doesn't work the way you want it to, but rather that there is no way to build your own prelude
Announcing a preliminary version of the Haskell 1.3 report. The Haskell 1.3 report is nearly complete. All technical issues appear to be resolved and the report is nearly ready. The report will be finalized April 19. Any comments must be submitted by April 15. We do not anticipate making
The Haskell 1.3 report is nearly done. The text of the report is complete - I'm working on indexing and web pages. We also have an initial cut at the Library Report. If you are interested in seeing the new report on the web, look at
The Haskell 1.3 Report is now complete. A web page with the entire report and other related information is at: http://haskell.cs.yale.edu/haskell-report/haskell-report.html This new report adds many new features to Haskell, including monadic I/O, standard libraries, constructor classes, labeled
Different Versions of Yale Haskell Compared --- There are currently three different platforms running Yale Haskell. Yale Haskell runs on Lucid Common Lisp, CMU Common Lisp, and AKCL. This document describes the differences between