arg_function: Check Function Argument

In arg: Clean and Simple Argument Checking

Check Function Argument

Description

Checks whether an argument is a function.

Usage

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

Arguments

x	the argument to be checked
.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_function(), arg_is()

Examples

f <- function(z) {
  arg_function(z)
}

try(f(print))   # No error
try(f("print")) # Error: must be a function

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