Computes expectation for a given ditribution
expect(spec, a, b, ...)
a character string specifying the distribution (for example, "norm" corresponds to the standard normal)
the lower end point of the distribution specified by spec
the upper end point of the distribution specified by spec
other parameters
A scalar, giving the expected value of the distribution specified by spec
S. Chan and S. Nadarajah, Risk: An R package for risk measures, submitted