[Haskell-cafe] looking for examples of non-full Functional Dependencies

Sittampalam, Ganesh ganesh.sittampalam at credit-suisse.com
Thu Apr 17 04:01:22 EDT 2008

Martin Sulzmann wrote:
> Mark P Jones wrote:

> > In fact, the two sets of dependencies that you have given here are 
> > provably equivalent, so it would be decidedly odd to have a "type 
> > improvement" system that distinguishes between them.

> Based on the FD-CHR formulation, for the single-range FD case we
> get [...] which is clearly weaker.
> [...]
> So, I conclude that in the Haskell type improvement context 
> there's clearly a difference among single-range and multi-range FDs.

This seems like a flaw in FD-CHR, rather than a fundamental difference 
between the dependencies.

> Of course, we could define multi-range FDs in terms of single-range FDs
> which then trivially solves the "equivalence" problem (but some user 
> may be disappointed that their multi-range FDs yield weaker improvement).

Why not instead transform single-range FDs into multi-range ones where


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