[Haskell] Quantified class constraints (& back-chaining)

[jeff p]

Hello,

> It's something I've wanted... Got a link for hereditary Harrop formulas
> so I can add them to my to-implement-when-Qhc-is-good-enough list?
> Google isn't telling me much about them except how to add support for
> constaints, which isn't terribly helpful.
>
This paper has a good description; it focuses on how to make a logic
programming language based on them.

    http://www.lix.polytechnique.fr/Labo/Dale.Miller/papers/apal91.pdf

-Jeff