A list, will be initialized after an instance is built.
Examples
# Instantiate
x <- rand_uniform()
e <- rand_normal()
test <- vi_model(prm = list(x = x, e = e),
prm_type = list(x = "r", e = "r"),
formula = y ~ 1 + x + x^2 + e)
test$prm
#> $x
#>
#> ── <RAND_UNIFORM object>
#> [a: 0, b: 1]
#>
#> $e
#>
#> ── <RAND_NORMAL object>
#> [mu: 0, sigma: 1]
#>
#> $y
#>
#> ── <CLOSED_FORM object>
#> EXPR = 1 + x + x^2 + e
#> - x: <RAND_UNIFORM object>
#> [a: 0, b: 1]
#> - e: <RAND_NORMAL object>
#> [mu: 0, sigma: 1]
#>