arg_formula: Check Formula Argument
In arg: Clean and Simple Argument Checking

arg_formula

R Documentation

Check Formula Argument

Description

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.

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

try(arg_formula(form1,
                one_sided = TRUE)) # No error
try(arg_formula(form2,
                one_sided = TRUE)) # Error, not one-sided

try(arg_formula(form1,
                one_sided = FALSE)) # Error, only one-sided
try(arg_formula(form2,
                one_sided = FALSE)) # No error

arg documentation built on April 9, 2026, 5:09 p.m.