greta_model_environment.R

library(greta)

# to be overwritten with correct method
greta_here <- function ()
  invisible(NULL)

# create an environment, and define the model there
greta_model <- function (model_expression,
                         parameters = list()) {
  env <- new.env()
  expr <- substitute(model_expression)
  
  # make sure the greta nodes are placed evaluated here
  local(greta_here(), envir = env)
  local(eval(expr), envir = env)
  
  
  # define and return the model object
  define_text <- paste('define_model(',
                       paste(parameters, collapse = ','),
                       ')')

  m <- local(eval(parse(text = define_text)),
             envir = env)
  
  m$defining_environment <- env
  m
  
}


model <- greta_model({
  
  intercept = normal(0, 5)
  coefficient = normal(0, 3)
  sd = lognormal(0, 3)
  mean <- intercept + coefficient * iris$Petal.Length
  likelihood(iris$Sepal.Length) = normal(mean, sd)
  
}, parameters = list('intercept', 'coefficient', 'sd'))

mcmc(model, n_samples = 100, warmup = 1)