Thanks for these pointers, Ken.&nbsp; And belated thanks to Oleg for his reply in June.&nbsp; Impressive tricks!<br><br>Perhaps I&#39;m not the only person who&#39;d prefer a more straightforward formulation of backtracking search?&nbsp; Cheers,
<br><br>&nbsp; - Conal<br><br><div><span class="gmail_quote">On 7/31/07, <b class="gmail_sendername">Chung-chieh Shan</b> &lt;<a href="mailto:ccshan@post.harvard.edu">ccshan@post.harvard.edu</a>&gt; wrote:</span><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
Conal Elliott &lt;<a href="mailto:conal@conal.net">conal@conal.net</a>&gt; wrote in article &lt;<a href="mailto:ea8ae9fb0707311208j9f3fcf7m92bef8f54aea3dd8@mail.gmail.com">ea8ae9fb0707311208j9f3fcf7m92bef8f54aea3dd8@mail.gmail.com
</a>&gt; in gmane.comp.lang.haskell.general:<br>&gt; I keep running into situations in which I want more powerful search in<br>&gt; selecting type class instances.<br><br>I agree that it&#39;s quite useful for instance search to backtrack, if not
<br>desirable in all cases.&nbsp;&nbsp;Proof search is program search, after all.<br><br>Of course, allowing undecidable instances, we can build backtracking<br>into instance search ourselves by representing the state of a<br>backtracking machine as a type.&nbsp;&nbsp;
<a href="http://okmij.org/ftp/Haskell/poly2.txt">http://okmij.org/ftp/Haskell/poly2.txt</a><br><br>--<br>Edit this signature at <a href="http://www.digitas.harvard.edu/cgi-bin/ken/sig">http://www.digitas.harvard.edu/cgi-bin/ken/sig
</a><br>And if thou gaze into the abyss, the abyss...actually finds you pretty creepy.<br><br>_______________________________________________<br>Haskell mailing list<br><a href="mailto:Haskell@haskell.org">Haskell@haskell.org
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