Basic numeric class.
The Haskell Report defines no laws for
Num. However,
(+) and
(*) are customarily expected
to define a ring and have the following properties:
- Associativity of (+) (x + y) +
z = x + (y + z)
- Commutativity of (+) x + y
= y + x
- fromInteger 0 is the additive
identity x + fromInteger 0 = x
- negate gives the additive inverse x +
negate x = fromInteger 0
- Associativity of (*) (x * y) *
z = x * (y * z)
- fromInteger 1 is the multiplicative
identity x * fromInteger 1 = x and
fromInteger 1 * x = x
- Distributivity of (*) with respect to
(+) a * (b + c) = (a * b) + (a *
c) and (b + c) * a = (b * a) + (c * a)
Note that it
isn't customarily expected that a type instance of
both
Num and
Ord implement an ordered ring. Indeed, in
base only
Integer and
Rational do.