to_lst: Ensure a list argument meets expectations

In stbl: Stabilize Function Arguments

Ensure a list argument meets expectations

Description

to_lst() checks whether an argument can be coerced to a list without losing information, returning it silently if so. Otherwise an informative error message is signaled. to_list() is a synonym of to_lst().

Usage

to_lst(x, ..., x_arg = caller_arg(x), call = caller_env())

to_list(x, ..., x_arg = caller_arg(x), call = caller_env())

## S3 method for class 'list'
to_lst(x, ...)

## Default S3 method:
to_lst(x, ..., x_arg = caller_arg(x), call = caller_env())

## S3 method for class ''NULL''
to_lst(x, ..., allow_null = TRUE, x_arg = caller_arg(x), call = caller_env())

## S3 method for class ''function''
to_lst(
  x,
  ...,
  coerce_function = FALSE,
  x_arg = caller_arg(x),
  call = caller_env()
)

Arguments

x	The argument to stabilize.
...	Arguments passed to base::as.list() or other methods.
x_arg	⁠(length-1 character)⁠ The name of the argument being stabilized to use in error messages. The automatic value will work in most cases, or pass it through from higher-level functions to make error messages clearer in unexported functions.
call	(environment) The execution environment to mention as the source of error messages.
allow_null	⁠(length-1 logical)⁠ Is NULL an acceptable value?
coerce_function	⁠(length-1 logical)⁠ Should functions be coerced?

Details

This function has important distinctions from base::as.list():

• Functions can be rejected as part of the call to this function (with coerce_function = FALSE, the default). If they are allowed, they'll be coerced to a list concatenating their formals and body (as with base::as.list().

• Primitive functions (such as base::is.na() or base::is.list()) always throw an error, rather than returning list(NULL).

• NULL values can be rejected as part of the call to this function (with allow_null = FALSE).

Value

The argument as a list.

See Also

Other list functions: specify_lst(), stabilize_lst(), stabilize_present()

stbl documentation built on April 4, 2026, 5:06 p.m.