These are shortcut methods for querying current bindings. For
example, arg_env(x) is equivalent to env(arg(x)),
is_forced(x, y) is equivalent to forced(arg_list(x,y)),
dots_exprs(...) is equivalent to exprs(dots(...)), and so
on. The shortcut forms skip the construction of the
intermediate quotation objects.
is_default determines whether an argument is bound to the
function's default value for that argument. It must be called
before the arguments have been forced (afterwards it will return
FALSE).
arg_env(sym, env = arg_env_(quote(sym), environment()))arg_env_(sym, env = arg_env_(quote(sym), environment()))
arg_expr(sym, env = arg_env_(quote(sym), environment()))
arg_expr_(sym, env = arg_env_(quote(sym), environment()))
dots_envs(...)
dots_exprs(...)
is_forced(...)
is_forced_(syms, envs)
is_literal(...)
is_literal_(syms, envs)
is_missing(...)
is_missing_(syms, envs, recursive = TRUE)
is_promise(...)
is_promise_(syms, envs)
is_default(...)
is_default_(syms, envs = arg_env(syms))
For arg_env, etc, a bare name (not forced). For the
normally evaluating arg_env_ and so on, name.
The environment to search in.
Bare variable names (for is_*_) or expressions (for
dots_*). Not forced.
A character vector or list of symbols.
An environment or list of environments.
Whether to recursively unwrap before testing for missingness.
arg_expr extracts an expression from a named argument.
dots_exprs(...) is equivalent to exprs(dots(...)) (which
is nearly equivalent to alist(...).)
is_literal(x) returns TRUE if x could be a source
literal. Specifically this tests whether it is X is bound to a
singleton vector or a missing_value.
is_missing(...) checks whether a variable is missing,
without forcing. It is similar to missing but can take
multiple arguments.
is_promise returns TRUE if the given variable is bound to
a promise. Not all arguments are bound to promises; byte-compiled
code often omits creating a promise for literal arguments
is_default returns a logical vector.