Produces a minimal R script that, when executed, recreates the recipe from
scratch. The output is a single declarative omop_recipe(...)
expression whose arguments are nested calls to the leaf constructors
(omop_variable*, omop_filter*, omop_output,
omop_population, omop_variable_block). Does not include
library() calls or header comments.
Examples
if (FALSE) { # \dontrun{
code <- recipe_to_code(recipe)
cat(code)
} # }