This might be better answered at the haskell-cafe. Sending to cafe. On 21 March 2015 at 03:09, Stuart Hungerford wrote:

Hi,

As a learning exercise I'm modelling some algebraic structures as Haskell typeclasses. Some of these are multi-parameter type classes. Here's a very simplified version of the type class relationships:

class MM a where one :: a

class AM a where zero :: a

class (AM a, MM a) => SR a

class (AM a) => AG a where inv :: a -> a

class (SR a) => R a where neg :: a -> a

class (R r, AG g) => M r g where sca :: r -> g -> g

check :: (Eq g, M r g) => g -> Bool check x = sca one x == x

The problem I have is that GHC is finding the "r" type variable in the "check" function ambiguous. Given my still limited Haskell knowledge I'm not surprised this is happening. What I would like to know is how experienced Haskellers handle this situation in practice: is there an idiomatic way of disambiguating "r" or is it a sign of poor type class design?

Thanks,

Stu _______________________________________________ Beginners mailing list Beginners@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners

-- Regards Sumit Sahrawat