library(parsnip)

set_new_model("potato")
set_model_mode(model = "potato", mode = "classification")

set_fit(
  model = "potato",
  eng = "potato",
  mode = "classification",
  value = list(
    interface = "formula",
    protect = c("formula", "data"),
    func = c(pkg = "potato", fun = "potato"),
    defaults = list()
  )
)
#> Error: The combination of 'potato' and mode 'classification' has not been registered for model 'potato'.
#> Backtrace:
#>     █
#>  1. └─parsnip::set_fit(...)

set_model_engine(
  "potato", 
  mode = "classification", 
  eng = "potato"
)

set_dependency("potato", eng = "potato")
#> Error: Please supply a single character value for the package name.
#> Backtrace:
#>     █
#>  1. └─parsnip::set_dependency("potato", eng = "potato")
#>  2.   └─parsnip:::check_pkg_val(pkg) /Volumes/Data1TB/Google Drive/data_science/rstudio/parsnip/R/aaa_models.R:522:2

set_fit(
  model = "potato",
  eng = "potato",
  mode = "classification",
  value = list(
    interface = "formula",
    protect = c("formula", "data"),
    func = c(pkg = "potato", fun = "potato"),
    defaults = list()
  )
)

set_fit(
  model = "potato",
  eng = "potato",
  mode = "classification",
  value = list(
    interface = "formula",
    protect = c("formula", "data"),
    func = c(pkg = "potato", fun = "potato"),
    defaults = list()
  )
)
#> Error: The combination of 'potato' and mode 'classification' already has a fit component for model 'potato'.
#> Backtrace:
#>     █
#>  1. └─parsnip::set_fit(...)