Signal has a lot of bogus instances

[ghost]

The following instances are mostly filled with bottoms:

instance (Rep a, Eq a) => Eq (Signal c a)
instance (Rep a, Enum a) => Enum (Signal i a)
instance (Ord a, Rep a) => Ord (Signal i a)
instance (Rep a, Real a) => Real (Signal i a)

It seems that min and max aren't used, the implementation of min looks odd (primS2 max?). So these instances are all to support Num and Integral, at the cost of deferring type errors to runtime. Are you sure that's worth it?