This is the type class of an ordered ring, satisfying the laws
a * b === b * a
a + (max b c) === max (a+b) (a+c)
negate (max b c) === min (negate b) (negate c)
a * (max b c) === max (a*b) (a*c) where a >= 0
Note that abs is in a rather different place than it is in the Haskell
98 Prelude. In particular,
abs :: Complex > Complex
is not defined. To me, this seems to have the wrong type anyway;
Complex.magnitude has the correct type.
Note:
The abs function can be defined for Additive and Ord,
the Ring constraint is not needed.
We may move signum to the new RealRing class.
