Downloads R in app_dir. If it has already been downloaded, get_R will use that file. If the download fails it will stop.
get_R(app_dir = getwd(), R_version = paste0(">=", R.version$major, ".",
R.version$minor))Development app's directory, defaults to getwd().
R version to use. Supports inequalities. Defaults to: paste0(">=", R.version$major, '.', R.version$minor).
sprintf('R-%s-win.exe', R_version) in app_dir.
If create_app(include_R = TRUE), then get_R.
get_R, copy_installation, create_config, create_bat, directives_section, setup_section, languages_section, tasks_section, files_section, icons_section, run_section, and code_section.