pre-action-variables.md
In workflows: Modeling Workflows

cannot add variables if a recipe already exists

Code
  add_variables(wf, y, x)
Condition
  Error in `add_variables()`:
  ! Variables cannot be added when a recipe already exists.

cannot add variables if a formula already exist

Code
  add_variables(wf, y, x)
Condition
  Error in `add_variables()`:
  ! Variables cannot be added when a formula already exists.

informative error if either `predictors` or `outcomes` aren't provided (#144)

Code
  add_variables(workflow(), outcomes = mpg)
Condition
  Error in `workflow_variables()`:
  ! `predictors` can't be missing.

Code
  add_variables(workflow(), predictors = mpg)
Condition
  Error in `workflow_variables()`:
  ! `outcomes` can't be missing.

cannot add two variables

Code
  add_variables(workflow, mpg, cyl)
Condition
  Error in `add_variables()`:
  ! A `variables` action has already been added to this workflow.

Code
  add_variables(workflow, variables = workflow_variables(mpg, cyl))
Condition
  Error in `add_variables()`:
  ! A `variables` action has already been added to this workflow.

can only use a 'xy_blueprint' blueprint

Code
  add_variables(workflow, mpg, cyl, blueprint = blueprint)
Condition
  Error in `add_variables()`:
  ! `blueprint` must be a hardhat 'xy_blueprint'.