Statistics.meanMethod
mean(::ClosedFormExpectation, f, q)

Compute the E_q[f(x)] where q is a distribution and f is a function.

Statistics.meanMethod
mean(::ClosedWilliamsProduct, f, q)

Suppose q is a distribution with density parameterized by θ and f is a function.

Compute the Eq[f(x) ∇θ log q(x; θ)] where q is a distribution and f is a function.