[Haskell] Re: type class instance selection & search

[Chung-chieh Shan]

Conal Elliott <conal at conal.net> wrote in article <ea8ae9fb0707311208j9f3fcf7m92bef8f54aea3dd8 at mail.gmail.com> in gmane.comp.lang.haskell.general:
> I keep running into situations in which I want more powerful search in
> selecting type class instances.

I agree that it's quite useful for instance search to backtrack, if not
desirable in all cases.  Proof search is program search, after all.

Of course, allowing undecidable instances, we can build backtracking
into instance search ourselves by representing the state of a
backtracking machine as a type.  http://okmij.org/ftp/Haskell/poly2.txt

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