On Mon, Jun 6, 2011 at 7:52 AM, Yitzchak Gale <[email protected]> wrote: > Scott Lawrence wrote: >> More specifically, I have >> >> class Model m a | m -> a where ... >> class Entropy d where ... >> instance (Model m a) => Entropy m where ... >> >> The first line requires MultiParamTypeClasses and >> FunctionalDependencies... the third >> requires UndecidableInstances... >> Is this likely to cause a problem? > > Yes. > > You almost never want to use UndecidableInstances > when writing practical programs in Haskell. > When GHC tells you that you need them, it almost > always means that your types are poorly designed, > usually due to influence from previous experience > with OOP. > > Your best bet is to step back and think again about > the problem you are trying to solve. What is the > best way to formulate the problem functionally? > That will lead you in the right direction. Please > feel free to share more details about what you are > trying to do. We would be happy to help you work out > some good directions.
Are you sure you weren't thinking of OverlappingInstances here? I haven't seen as much scorn heaped upon Undecidable. > > Regards, > Yitz > > _______________________________________________ > Haskell-Cafe mailing list > [email protected] > http://www.haskell.org/mailman/listinfo/haskell-cafe > -- Work is punishment for failing to procrastinate effectively. _______________________________________________ Haskell-Cafe mailing list [email protected] http://www.haskell.org/mailman/listinfo/haskell-cafe
