One-dimensional Gaussian distribution with mean and variance sampled from Gaussian/gamma priors

```
(define xdata '(1 1.2 1.5 0.8 0.9 1 1.3 0.9))
(define samples
(mh-query
1000 10
(define mu (gaussian 0 2))
(define sigma-squared (gamma 1 1))
mu
(all
(map (lambda (x) (equal? (gaussian mu sigma-squared x) x)) xdata)
)))
(density samples "Posterior over mu" #t)
```