A callable object is an object that can appear in the function position of a call (as opposed to argument position). This includes symbolic objects that evaluate to a function or literal functions embedded in the call.




An object to test.


Note that strings may look like callable objects because expressions of the form "list"() are valid R code. However, that's only because the R parser transforms strings to symbols. It is not legal to manually set language heads to strings.


# Symbolic objects and functions are callable: is_callable(quote(foo))
#> [1] TRUE
#> [1] TRUE
# node_poke_car() lets you modify calls without any checking: lang <- quote(foo(10)) node_poke_car(lang, current_env()) # Use is_callable() to check an input object is safe to put as CAR: obj <- base::identity if (is_callable(obj)) { lang <- node_poke_car(lang, obj) } else { abort("`obj` must be callable") } eval_bare(lang)
#> [1] 10