I want to save a `mcmc()`

output so I do not need to rerun it next time. However, using `saveRDS()`

(or `save()`

) seems to decouple the `greta_mcmc_list`

object from other `greta_array`

s.

Example code:

First, run this:

```
library(greta)
alpha <- normal(0, 1)
beta <- normal(0, 1)
sigma <- lognormal(1, 0.1)
y <- as_data(iris$Petal.Width)
mu <- alpha + iris$Petal.Length * beta
distribution(y) <- normal(mu, sigma)
m <- model(alpha, beta, sigma)
draws <- mcmc(m, n_samples = 500)
# save draws as rds so do not need to rerun mcmc every time
saveRDS(draws, file = "draws.rds")
```

Then restart the session and load the `greta_mcmc_list`

object. This will fail halfway:

```
library(greta)
draws <- readRDS(file = "draws.rds")
# the codes below breaks
petal_length_plot <- seq(min(iris$Petal.Length),
max(iris$Petal.Length),
length.out = 100)
mu_plot <- alpha + petal_length_plot * beta
mu_plot_draws <- calculate(mu_plot, values = draws)
mu_est <- colMeans(mu_plot_draws[[1]])
plot(mu_est ~ petal_length_plot, type = "n",
ylim = range(mu_plot_draws[[1]]))
apply(mu_plot_draws[[1]], 1, lines,
x = petal_length_plot, col = grey(0.8))
lines(mu_est ~ petal_length_plot, lwd = 2)
```

You should get an error:

```
Error: the target greta arrays do not appear to be connected to those in the greta_mcmc_list object
```

Did I do something wrong?