[Haskell-cafe] Dealing with incoherent instances

Vyacheslav Akhmechet coffeemug at gmail.com
Wed Dec 27 20:23:44 EST 2006

Ok, I think I solved the problem. It actually simplified my design and
made it significantly cleaner and nicer :) I won't bore people with
the code/explanation here but I'll publish an article about it on

Actually what I was trying to do is described in the SYB 3 paper.

- Slava.

On 12/27/06, Bulat Ziganshin <bulat.ziganshin at gmail.com> wrote:
> Hello Vyacheslav,
> (returning to cafe)
> Wednesday, December 27, 2006, 6:10:30 PM, you wrote:
> > Ah, so the moment something is passed through a polymorphic function
> > its type information is lost... This seems like a bug in the
> > specification/implementation, no? This is most certainly not the
> > desired behavior. It seems like the compiler has all the information
> > it needs but still can't select the right instance.
> sorry, but i think that it is how type class system should work in this
> case. look at the page for details
> > Are there ways to get around this problem?
> existential types, for example. we need exact specification of your
> problem. "show me the code"
> >> are you seen http://haskell.org/haskellwiki/OOP_vs_type_classes ?
> --
> Best regards,
>  Bulat                            mailto:Bulat.Ziganshin at gmail.com

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