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Check if an object can be safely coerced to a function

Source: R/are_fn_ish.R
are_fn_ish.Rd

are_fn_ish() is a vectorized predicate function that checks whether each element of its input can be safely coerced to a function. are_function_ish() is a synonym of are_fn_ish().

is_fn_ish() is a scalar predicate that checks whether its input can be safely coerced to a function by to_fn(). is_function_ish() is a synonym of is_fn_ish().

Usage

are_fn_ish(x, ...)

are_function_ish(x, ...)

is_fn_ish(x, ...)

is_function_ish(x, ...)

Arguments

x

The object to check.

...

Arguments passed to methods.

Value

are_fn_ish() returns a logical vector with the same length as the input. is_fn_ish() returns a length-1 logical (TRUE or FALSE).

Details

are_fn_ish() returns TRUE for:

  • Functions (including lambda functions created with ~ or \())

  • Formulas (one-sided or two-sided, coercible via rlang::as_function())

  • Character strings that are syntactically valid function names: either a bare name ("mean") or a namespaced name ("pkg::fn"). The check is syntactic; it does not verify that the named function exists in any environment.

is_fn_ish() returns TRUE for objects that to_fn() can coerce without error (assuming a matching function exists in the search path):

  • Functions (including lambda functions created with ~ or \())

  • One-sided or two-sided formulas

  • Single non-NA character strings (including namespaced "pkg::fn" names)

NULL and length-0 character vectors are not considered function-ish because they do not represent a callable object; to_fn() converts them to NULL only as a permissive special case controlled by allow_null.

See also

Other function functions: to(), to_fn()

Other check functions: are_chr_ish(), are_dbl_ish(), are_fct_ish(), are_int_ish(), are_lgl_ish()

Examples

are_fn_ish(mean)
#> [1] TRUE
are_fn_ish(~ . + 1)
#> [1] TRUE
are_fn_ish(c("mean", "stats::median", NA, "", "1bad"))
#> [1]  TRUE  TRUE FALSE FALSE FALSE
are_fn_ish(NULL)
#> logical(0)
are_fn_ish(1L)
#> [1] FALSE

is_fn_ish(mean)
#> [1] TRUE
is_fn_ish("mean")
#> [1] TRUE
is_fn_ish("stats::median")
#> [1] TRUE
is_fn_ish(~ . + 1)
#> [1] TRUE
is_fn_ish(NULL)
#> [1] FALSE
is_fn_ish(1L)
#> [1] FALSE