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Check Formula Argument

Source: R/arg_formula.R
arg_formula.Rd

Checks whether an argument is a formula.

Usage

arg_formula(
  x,
  one_sided = NULL,
  .arg = rlang::caller_arg(x),
  .msg = NULL,
  .call
)

Arguments

x

the argument to be checked

one_sided

NULL or logical; if TRUE, checks that x is a formula with only one side (the right side); if FALSE, checks that x is a formula with both sides; if NULL (the default), checks only that x is a formula.

.arg

the name of the argument supplied to x to appear in error messages. The default is to extract the argument's name using rlang::caller_arg(). Ignored if .msg is supplied.

.msg

an optional alternative message to display if an error is thrown instead of the default message.

.call

the execution environment of a currently running function, e.g. .call = rlang::current_env(). The corresponding function call is retrieved and mentioned in error messages as the source of the error. Passed to err(). Set to NULL to omit call information. The default is to search along the call stack for the first user-facing function in another package, if any.

Value

Returns NULL invisibly if an error is not thrown.

See also

rlang::is_formula(), arg_is()

Examples

form1 <- ~a + b
form2 <- y ~ a + b
not_form <- 1:3

try(arg_formula(form1))    # No error
try(arg_formula(form2))    # No error
try(arg_formula(not_form)) # Error: not a formula
#> Error : `not_form` must be a formula.

try(arg_formula(form1,
                one_sided = TRUE)) # No error
try(arg_formula(form2,
                one_sided = TRUE)) # Error, not one-sided
#> Error : `form2` must be a one-sided formula.

try(arg_formula(form1,
                one_sided = FALSE)) # Error, only one-sided
#> Error : `form1` must be a two-sided formula.
try(arg_formula(form2,
                one_sided = FALSE)) # No error