Relax superclasses for instance Arbitrary Compose

[Bodigrim]

Currently we define

quickcheck/src/Test/QuickCheck/Arbitrary.hs

Lines 1016 to 1018 in 3c2d0d8

	instance (Arbitrary1 f, Arbitrary1 g, Arbitrary a) => Arbitrary (Compose f g a) where
	arbitrary = arbitrary1
	shrink = shrink1

That's more restrictive than it can be, it would be nice to relax the constraint to Arbitrary (f (g a)) as in

instance Arbitrary (f (g a)) => Arbitrary (Compose f g a) where 
  arbitrary = Compose <$> arbitrary
  shrink (Compose x) = map Compose (shrink x)

This would bring the approach in line with how base defines all other instances for Compose:

instance Num (f (g a)) => Num (Compose f g a) 	
instance Read (f (g a)) => Read (Compose f g a) 	
instance Fractional (f (g a)) => Fractional (Compose f g a) 	
instance Integral (f (g a)) => Integral (Compose f g a) 	
instance Real (f (g a)) => Real (Compose f g a) 	
instance RealFrac (f (g a)) => RealFrac (Compose f g a) 	
instance Show (f (g a)) => Show (Compose f g a)

[MaximilianAlgehed]

I don't see why not!

I guess it risks breaking some super esoteric constraint solver hack in some code somewhere. But that's a price I think might be worth paying to be in line with how base does things and to be more permissive.