Re: [Haskell-cafe] Enforcing data structures invariant in the type system

Nicola Gigante writes:

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Il giorno 30/mar/2015, alle ore 19:17, Oliver Charles ha scritto:

You're in the right ballpark that's for sure - and your experience with hard-to-decode error messages is not a new one either! Haskell is somewhat "experiemental" in this domain, as its only now starting to learn the features necessary to do what you want to do.

Having some compilers background I understand very well the difficulties in making sensible error messages, especially when dealing with such advanced features. The point was more that I don’t know the basics on how those features work (and what is involved in the job of the type checker) so I can’t even parse what GHC try to tell me (skolem what?).

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I think some of the best work to learn the latest techniques is described here: https://github.com/jstolarek/dep-typed-wbl-heaps-hs https://github.com/jstolarek/dep-typed-wbl-heaps-hs

Thank you that looks very useful!

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-- ocharles

Greetings, Nicola _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe

Stephanie Stephanie Weirich gave an invited talk about maintaining color and height invariants for Red-Black trees at ICFP this year [1]. Connor McBride had a talk and paper about also maintinging order invariants [2]. You might want to have a look at them. As for getting used to the error messages. I think the only way to learn is to get your hands dirty yourself. I can highly reccommend also just doing the red-black trees yourself. Getting insertions to work is not too difficult. Deletions are a bit harder. I also did so some time ago [3] (before seeing the ICFP talk even; I found it very cool that I had pretty much the same solution :)). Regards, [1] https://www.youtube.com/watch?v=rhWMhTjQzsU&index=22&list=PL4UWOFngo5DVBqifWX6ZlXJ7idxWaOP69 [2] https://www.youtube.com/watch?v=pNBPCnZEdSs [3] http://fstaals.net/RedBlackTree.html -- - Frank