Closed form expression of y

A quoted formula, will be passed to CLOSED_FORM$instantiate to define a closed form expression for y.

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,
                 null_formula = y ~ x,
                 alt_formula = y ~ x + I(x^2))

# A formula with environment equals to `test`
test$formula
#> y ~ 1 + x + x^2 + e

# `y` has the same expression
test$prm$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]