Hypothetical reasoning in type classes

[Ken Shan]

On 2003-11-13T13:19:28-0000, Simon Peyton-Jones wrote:
> | From: haskell-cafe-bounces at haskell.org
> | 
> | Has anyone thought about adding hereditary Harrop formulas, in other
> | words hypothetical reasoning and universal quantification, to the
> | instance contexts in the Hsakell type class system?
> 
> Yes, absolutely.  See
> 	http://research.microsoft.com/~simonpj/Papers/derive.htm
> Section 7, and Trifanov's paper at the Haskell Workshop 2003

Thanks for the pointers!  I am now thinking about encoding SML-style
module systems into Haskell using type classes with functional
dependencies.  For this purpose, I seem to need hereditary Harrop
formulas in instance contexts.  I wonder if such encodings have been
proposed previously in the literature?  The closest I was able to find
is Kahl and Scheffczyk's paper at the 2001 Haskell Workshop.

Thanks again,
	Ken

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