spec_is_possible: Model Specification Checking:

Description

The helpers spec_is_possible(), spec_is_loaded(), and prompt_missing_implementation() provide tooling for checking model specifications. In addition to the spec, engine, and mode arguments, the functions take arguments user_specified_engine and user_specified_mode, denoting whether the user themselves has specified the engine or mode, respectively.

Usage

spec_is_possible(
  spec,
  engine = spec$engine,
  user_specified_engine = spec$user_specified_engine,
  mode = spec$mode,
  user_specified_mode = spec$user_specified_mode
)
spec_is_loaded(
  spec,
  engine = spec$engine,
  user_specified_engine = spec$user_specified_engine,
  mode = spec$mode,
  user_specified_mode = spec$user_specified_mode
)
prompt_missing_implementation(
  spec,
  engine = spec$engine,
  user_specified_engine = spec$user_specified_engine,
  mode = spec$mode,
  user_specified_mode = spec$user_specified_mode,
  prompt,
  ...
)

Arguments

Details

spec_is_possible() checks against the union of

the current parsnip model environment and
the model_info_table of "pre-registered" model specifications

to determine whether a model is well-specified. See parsnip:::model_info_table for this table.

spec_is_loaded() checks only against the current parsnip model environment.

spec_is_possible() is executed automatically on new_model_spec(), set_mode(), and set_engine(), and spec_is_loaded() is executed automatically in print.model_spec(), among other places. spec_is_possible() should be used when a model specification is still "in progress" of being specified, while spec_is_loaded should only be called when parsnip or an extension receives some indication that the user is "done" specifying a model specification: at print, fit, addition to a workflow, or extract_*(), for example.

When spec_is_loaded() is FALSE, the prompt_missing_implementation() helper will construct an informative message to prompt users to load or install needed packages. It's prompt argument refers to the prompting function to use, usually cli::cli_inform or cli::cli_abort, and the ellipses are passed to that function.