Abstraction of numeric types that may be raised to a power using the exponentiation operator ^.

function exp(Float x) => e^x;

The exponentiation operation should obey the usual index laws, including:

• x^0 = 1,
• x^1 = x,
• x^(-1) = 1/x
• x^(m+n) = x^m * x^n
• x^(m-n) = x^m / x^n
• x^(m*n) = (x^m)^n
• (x*y)^n = x^n * y^n

where 0 is the additive identity, and 1 is the multiplicative identity.

Note that in general, the type of the exponent may be different to the numeric type which is exponentiated. For example, a Rational number class might be a subtype of Exponentiable<Rational,Integer>, thus accepting only whole-number exponents.