The R language defines two different types of functions: primitive functions, which are low-level, and closures, which are the regular kind of functions.

is_function(x)

is_closure(x)

is_primitive(x)

is_primitive_eager(x)

is_primitive_lazy(x)

Arguments

x

Object to be tested.

Details

Closures are functions written in R, named after the way their arguments are scoped within nested environments (see https://en.wikipedia.org/wiki/Closure_(computer_programming)). The root environment of the closure is called the closure environment. When closures are evaluated, a new environment called the evaluation frame is created with the closure environment as parent. This is where the body of the closure is evaluated. These closure frames appear on the evaluation stack (see ctxt_stack()), as opposed to primitive functions which do not necessarily have their own evaluation frame and never appear on the stack.

Primitive functions are more efficient than closures for two reasons. First, they are written entirely in fast low-level code. Second, the mechanism by which they are passed arguments is more efficient because they often do not need the full procedure of argument matching (dealing with positional versus named arguments, partial matching, etc). One practical consequence of the special way in which primitives are passed arguments is that they technically do not have formal arguments, and formals() will return NULL if called on a primitive function. Finally, primitive functions can either take arguments lazily, like R closures do, or evaluate them eagerly before being passed on to the C code. The former kind of primitives are called "special" in R terminology, while the latter is referred to as "builtin". is_primitive_eager() and is_primitive_lazy() allow you to check whether a primitive function evaluates arguments eagerly or lazily.

You will also encounter the distinction between primitive and internal functions in technical documentation. Like primitive functions, internal functions are defined at a low level and written in C. However, internal functions have no representation in the R language. Instead, they are called via a call to base::.Internal() within a regular closure. This ensures that they appear as normal R function objects: they obey all the usual rules of argument passing, and they appear on the evaluation stack as any other closures. As a result, fn_fmls() does not need to look in the .ArgsEnv environment to obtain a representation of their arguments, and there is no way of querying from R whether they are lazy ('special' in R terminology) or eager ('builtin').

You can call primitive functions with .Primitive() and internal functions with .Internal(). However, calling internal functions in a package is forbidden by CRAN's policy because they are considered part of the private API. They often assume that they have been called with correctly formed arguments, and may cause R to crash if you call them with unexpected objects.

Examples

# Primitive functions are not closures: is_closure(base::c)
#> [1] FALSE
is_primitive(base::c)
#> [1] TRUE
# On the other hand, internal functions are wrapped in a closure # and appear as such from the R side: is_closure(base::eval)
#> [1] TRUE
# Both closures and primitives are functions: is_function(base::c)
#> [1] TRUE
is_function(base::eval)
#> [1] TRUE
# Primitive functions never appear in evaluation stacks: is_primitive(base::`[[`)
#> [1] TRUE
is_primitive(base::list)
#> [1] TRUE
list(ctxt_stack())[[1]]
#> [[1]] #> <frame 24> (23) #> expr: eval(expr, envir, enclos) #> env: [local 0x5613d2ed81e0] #> #> [[2]] #> <frame 23> (13) #> expr: eval(expr, envir, enclos) #> env: [local 0x5613d3fd76d0] #> #> [[3]] #> <frame 22> (13) #> expr: withVisible(eval(expr, envir, enclos)) #> env: [local 0x5613d3fd7900] #> #> [[4]] #> <frame 21> (13) #> expr: withCallingHandlers(withVisible(eval(expr, envir, enclos)), warning = wHandler, <...> #> env: [local 0x5613d3fd4080] #> #> [[5]] #> <frame 20> (19) #> expr: doTryCatch(return(expr), name, parentenv, handler) #> env: [local 0x5613d3fd4630] #> #> [[6]] #> <frame 19> (18) #> expr: tryCatchOne(expr, names, parentenv, handlers[[1L]]) #> env: [local 0x5613d3fd4978] #> #> [[7]] #> <frame 18> (17) #> expr: tryCatchList(expr, classes, parentenv, handlers) #> env: [local 0x5613d3fd4cc0] #> #> [[8]] #> <frame 17> (16) #> expr: tryCatch(expr, error = function(e) { <...> #> env: [local 0x5613d3fd53c0] #> #> [[9]] #> <frame 16> (15) #> expr: try(f, silent = TRUE) #> env: [local 0x5613d3fd55f0] #> #> [[10]] #> <frame 15> (13) #> expr: handle(ev <- withCallingHandlers(withVisible(eval(expr, envir, <...> #> env: [local 0x5613d3fd5778] #> #> [[11]] #> <frame 14> (13) #> expr: timing_fn(handle(ev <- withCallingHandlers(withVisible(eval(expr, <...> #> env: [local 0x5613d3fd5858] #> #> [[12]] #> <frame 13> (12) #> expr: evaluate_call(expr, parsed$src[[i]], envir = envir, enclos = enclos, <...> #> env: [frame 0x5613d3fc60e0] #> #> [[13]] #> <frame 12> (11) #> expr: evaluate::evaluate(code, child_env(env), new_device = TRUE) #> env: [frame 0x5613d1b9f538] #> #> [[14]] #> <frame 11> (10) #> expr: downlit::evaluate_and_highlight(code, fig_save = fig_save_topic, <...> #> env: [frame 0x5613d1ba0b50] #> #> [[15]] #> <frame 10> (9) #> expr: highlight_examples(code, topic, env = env) #> env: [frame 0x5613d1b70648] #> #> [[16]] #> <frame 9> (8) #> expr: run_examples(tags$tag_examples[[1]], env = new.env(parent = globalenv()), <...> #> env: [frame 0x5613d467ac20] #> #> [[17]] #> <frame 8> (6) #> expr: data_reference_topic(topic, pkg, examples = examples, run_dont_run = run_dont_run) #> env: [frame 0x5613d2fab380] #> #> [[18]] #> <frame 7> (6) #> expr: withCallingHandlers(data_reference_topic(topic, pkg, examples = examples, <...> #> env: [frame 0x5613d2faba80] #> #> [[19]] #> <frame 6> (5) #> expr: .f(.x[[i]], ...) #> env: [frame 0x5613d41e87c8] #> #> [[20]] #> <frame 5> (4) #> expr: purrr::map(topics, build_reference_topic, pkg = pkg, lazy = lazy, <...> #> env: [frame 0x5613d13ff368] #> #> [[21]] #> <frame 4> (3) #> expr: build_reference(pkg, lazy = lazy, examples = examples, run_dont_run = run_dont_run, <...> #> env: [frame 0x5613d1251d38] #> #> [[22]] #> <frame 3> (2) #> expr: build_site_local(pkg = pkg, examples = examples, run_dont_run = run_dont_run, <...> #> env: [frame 0x5613d0943bf8] #> #> [[23]] #> <frame 2> (1) #> expr: build_site(pkg, devel = FALSE, preview = FALSE, install = FALSE, <...> #> env: [frame 0x5613d09411d8] #> #> [[24]] #> <frame 1> (0) #> expr: pkgdown::deploy_to_branch(new_process = FALSE) #> env: [frame 0x5613cdd7e6b0] #> #> [[25]] #> <frame 0> [global] #> expr: NULL #> env: [global] #> #> attr(,"class") #> [1] "ctxt_stack" "stack"
# While closures do: identity(identity(ctxt_stack()))
#> [[1]] #> <frame 26> (24) #> expr: identity(ctxt_stack()) #> env: [local 0x5613d43b8e78] #> #> [[2]] #> <frame 25> (24) #> expr: identity(identity(ctxt_stack())) #> env: [local 0x5613d43b8f90] #> #> [[3]] #> <frame 24> (23) #> expr: eval(expr, envir, enclos) #> env: [local 0x5613d2ed81e0] #> #> [[4]] #> <frame 23> (13) #> expr: eval(expr, envir, enclos) #> env: [local 0x5613d43b9150] #> #> [[5]] #> <frame 22> (13) #> expr: withVisible(eval(expr, envir, enclos)) #> env: [local 0x5613d43b9380] #> #> [[6]] #> <frame 21> (13) #> expr: withCallingHandlers(withVisible(eval(expr, envir, enclos)), warning = wHandler, <...> #> env: [local 0x5613d43b5ba8] #> #> [[7]] #> <frame 20> (19) #> expr: doTryCatch(return(expr), name, parentenv, handler) #> env: [local 0x5613d43b6120] #> #> [[8]] #> <frame 19> (18) #> expr: tryCatchOne(expr, names, parentenv, handlers[[1L]]) #> env: [local 0x5613d43b6468] #> #> [[9]] #> <frame 18> (17) #> expr: tryCatchList(expr, classes, parentenv, handlers) #> env: [local 0x5613d43b67b0] #> #> [[10]] #> <frame 17> (16) #> expr: tryCatch(expr, error = function(e) { <...> #> env: [local 0x5613d43b6eb0] #> #> [[11]] #> <frame 16> (15) #> expr: try(f, silent = TRUE) #> env: [local 0x5613d43b70e0] #> #> [[12]] #> <frame 15> (13) #> expr: handle(ev <- withCallingHandlers(withVisible(eval(expr, envir, <...> #> env: [local 0x5613d43b7268] #> #> [[13]] #> <frame 14> (13) #> expr: timing_fn(handle(ev <- withCallingHandlers(withVisible(eval(expr, <...> #> env: [local 0x5613d43b7348] #> #> [[14]] #> <frame 13> (12) #> expr: evaluate_call(expr, parsed$src[[i]], envir = envir, enclos = enclos, <...> #> env: [frame 0x5613d2ef2bc8] #> #> [[15]] #> <frame 12> (11) #> expr: evaluate::evaluate(code, child_env(env), new_device = TRUE) #> env: [frame 0x5613d1b9f538] #> #> [[16]] #> <frame 11> (10) #> expr: downlit::evaluate_and_highlight(code, fig_save = fig_save_topic, <...> #> env: [frame 0x5613d1ba0b50] #> #> [[17]] #> <frame 10> (9) #> expr: highlight_examples(code, topic, env = env) #> env: [frame 0x5613d1b70648] #> #> [[18]] #> <frame 9> (8) #> expr: run_examples(tags$tag_examples[[1]], env = new.env(parent = globalenv()), <...> #> env: [frame 0x5613d467ac20] #> #> [[19]] #> <frame 8> (6) #> expr: data_reference_topic(topic, pkg, examples = examples, run_dont_run = run_dont_run) #> env: [frame 0x5613d2fab380] #> #> [[20]] #> <frame 7> (6) #> expr: withCallingHandlers(data_reference_topic(topic, pkg, examples = examples, <...> #> env: [frame 0x5613d2faba80] #> #> [[21]] #> <frame 6> (5) #> expr: .f(.x[[i]], ...) #> env: [frame 0x5613d41e87c8] #> #> [[22]] #> <frame 5> (4) #> expr: purrr::map(topics, build_reference_topic, pkg = pkg, lazy = lazy, <...> #> env: [frame 0x5613d13ff368] #> #> [[23]] #> <frame 4> (3) #> expr: build_reference(pkg, lazy = lazy, examples = examples, run_dont_run = run_dont_run, <...> #> env: [frame 0x5613d1251d38] #> #> [[24]] #> <frame 3> (2) #> expr: build_site_local(pkg = pkg, examples = examples, run_dont_run = run_dont_run, <...> #> env: [frame 0x5613d0943bf8] #> #> [[25]] #> <frame 2> (1) #> expr: build_site(pkg, devel = FALSE, preview = FALSE, install = FALSE, <...> #> env: [frame 0x5613d09411d8] #> #> [[26]] #> <frame 1> (0) #> expr: pkgdown::deploy_to_branch(new_process = FALSE) #> env: [frame 0x5613cdd7e6b0] #> #> [[27]] #> <frame 0> [global] #> expr: NULL #> env: [global] #> #> attr(,"class") #> [1] "ctxt_stack" "stack"
# Many primitive functions evaluate arguments eagerly: is_primitive_eager(base::c)
#> [1] TRUE
is_primitive_eager(base::list)
#> [1] TRUE
is_primitive_eager(base::`+`)
#> [1] TRUE
# However, primitives that operate on expressions, like quote() or # substitute(), are lazy: is_primitive_lazy(base::quote)
#> [1] TRUE
is_primitive_lazy(base::substitute)
#> [1] TRUE