Hi,
I am trying to define a commutative operator :
(%+) :: a -> b -> c
(%+) :: b -> a -> c

instead of defining a class and instantiating twice every time, I am trying to do the following:

class Commutative a b c where
(%+) :: a -> b -> c

class Operation a b c | a b -> c where
(%+%) :: a -> b -> c

instance (Operation a b c) => Commutative a b c where
(%+) = (%+%)

instance (Operation b a c) => Commutative a b c where
(%+) = flip (%+%)

instance Operation Int (Maybe Int) Int where
i %+% (Just s) = i + s

---

With hugs -98 +mo
((2::Int) %+ (Just (2::Int)))::Int gives 4
But (2::Int) %+ (Just (2::Int)) is of type Commutative Int (Maybe Int) a => a. So is (Just (2::Int)) %+ (2::Int)

Is the dependency in Operation class not sufficient. Any work around?

Which flags to be set for Ghc to accept this code. I tried -fallow-overlapping-instances and
-fallow-undecidable-instances.

Thanks,
S