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

formula is validated

Code
  add_formula(workflow(), 1)
Condition
  Error in `add_formula()`:
  ! `formula` must be a formula.

cannot add a formula if a recipe already exists

Code
  add_formula(workflow, mpg ~ cyl)
Condition
  Error in `add_formula()`:
  ! A formula cannot be added when a recipe already exists.

cannot add a formula if variables already exist

Code
  add_formula(workflow, mpg ~ cyl)
Condition
  Error in `add_formula()`:
  ! A formula cannot be added when variables already exist.

cannot add two formulas

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

can't pass an `offset()` through `add_formula()` (#162)

Code
  fit(workflow, data = df)
Condition
  Error in `fit()`:
  ! Can't use an offset in the formula supplied to `add_formula()`.
  i Instead, specify offsets through a model formula in `add_model(formula = )`.

can only use a 'formula_blueprint' blueprint

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