The Preface of the Haskell Report says: The comittee hopes that Haskell can serve as a basis for future research in language design. We hope that extensions or variants of the language may appear, incorporating experimental features. Various extensions have been proposed or even
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.
Dear sir, I had written several pages of Haskell scripts, tried HUGS Haskell on them, debugged, and now I'm trying to complile the stuff with Glasgow Haskell. ghc-0.25 dislikes the following declarations: - module M where instance (Num a, Num b) =