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. See fn_fmls() for a function that returns a representation of formal arguments for primitive functions. 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
#> [[1]] #> <frame 37> (36) #> expr: eval(expr, envir, enclos) #> env: [local 0x5e9c150] #> #> [[2]] #> <frame 36> (26) #> expr: eval(expr, envir, enclos) #> env: [local 0x50febd8] #> #> [[3]] #> <frame 35> (26) #> expr: withVisible(eval(expr, envir, enclos)) #> env: [local 0x50fd5c0] #> #> [[4]] #> <frame 34> (26) #> expr: withCallingHandlers(withVisible(eval(expr, envir, enclos)), warning = wHandler, <...> #> env: [local 0x5101240] #> #> [[5]] #> <frame 33> (32) #> expr: doTryCatch(return(expr), name, parentenv, handler) #> env: [local 0x51030b8] #> #> [[6]] #> <frame 32> (31) #> expr: tryCatchOne(expr, names, parentenv, handlers[[1L]]) #> env: [local 0x5105d30] #> #> [[7]] #> <frame 31> (30) #> expr: tryCatchList(expr, classes, parentenv, handlers) #> env: [local 0x510a938] #> #> [[8]] #> <frame 30> (29) #> expr: tryCatch(expr, error = function(e) { <...> #> env: [local 0x510b828] #> #> [[9]] #> <frame 29> (28) #> expr: try(f, silent = TRUE) #> env: [local 0x5111f98] #> #> [[10]] #> <frame 28> (26) #> expr: handle(ev <- withCallingHandlers(withVisible(eval(expr, envir, <...> #> env: [local 0x5111630] #> #> [[11]] #> <frame 27> (26) #> expr: timing_fn(handle(ev <- withCallingHandlers(withVisible(eval(expr, <...> #> env: [local 0x5111518] #> #> [[12]] #> <frame 26> (25) #> expr: evaluate_call(expr, parsed$src[[i]], envir = envir, enclos = enclos, <...> #> env: [frame 0x5170e60] #> #> [[13]] #> <frame 25> (22) #> expr: evaluate::evaluate(code, env, new_device = TRUE) #> env: [frame 0x7585c18] #> #> [[14]] #> <frame 24> (23) #> expr: force(code) #> env: [frame 0x6d16e58] #> #> [[15]] #> <frame 23> (22) #> expr: withr::with_options(list(crayon.enabled = getOption("crayon.enabled", <...> #> env: [frame 0x7751bf0] #> #> [[16]] #> <frame 22> (21) #> expr: .f(code = .l[[c(1L, 1L)]], run = .l[[c(2L, 1L)]], show = .l[[c(3L, <...> #> env: [frame 0x78a50b8] #> #> [[17]] #> <frame 21> (20) #> expr: purrr::pmap_chr(list(code = code, run = run, show = show), format_example_chunk, <...> #> env: [frame 0x75de710] #> #> [[18]] #> <frame 20> (18) #> expr: as_data.tag_examples(tags$tag_examples[[1]], env = new.env(parent = globalenv()), <...> #> env: [frame 0x79d9630] #> #> [[19]] #> <frame 19> (18) #> expr: as_data(tags$tag_examples[[1]], env = new.env(parent = globalenv()), <...> #> env: [frame 0x79d8c20] #> #> [[20]] #> <frame 18> (17) #> expr: data_reference_topic(topic, pkg, examples = examples, run_dont_run = run_dont_run) #> env: [frame 0x8005468] #> #> [[21]] #> <frame 17> (16) #> expr: .f(.x[[i]], ...) #> env: [frame 0x88c8b90] #> #> [[22]] #> <frame 16> (15) #> expr: purrr::map(topics, build_reference_topic, pkg = pkg, lazy = lazy, <...> #> env: [frame 0x79ae7d0] #> #> [[23]] #> <frame 15> (14) #> expr: build_reference(pkg, lazy = lazy, document = document, examples = examples, <...> #> env: [frame 0x5078448] #> #> [[24]] #> <frame 14> (13) #> expr: build_site_local(pkg = pkg, examples = examples, document = document, <...> #> env: [frame 0x1ebac98] #> #> [[25]] #> <frame 13> (12) #> expr: pkgdown::build_site(...) #> env: [frame 0x1b2ad48] #> #> [[26]] #> <frame 12> (0) #> expr: (function (..., crayon_enabled, crayon_colors, pkgdown_internet) <...> #> env: [frame 0x36f02d0] #> #> [[27]] #> <frame 11> (0) #> expr: (function (what, args, quote = FALSE, envir = parent.frame()) <...> #> env: [frame 0x36f1290] #> #> [[28]] #> <frame 10> (0) #> expr: do.call(do.call, c(readRDS("/tmp/RtmpnyPeIi/file43227a57ff01"), <...> #> env: [frame 0x36e10f0] #> #> [[29]] #> <frame 9> (0) #> expr: saveRDS(do.call(do.call, c(readRDS("/tmp/RtmpnyPeIi/file43227a57ff01"), <...> #> env: [frame 0x36e1e80] #> #> [[30]] #> <frame 8> (0) #> expr: withCallingHandlers({ <...> #> env: [frame 0x36dcc58] #> #> [[31]] #> <frame 7> (6) #> expr: doTryCatch(return(expr), name, parentenv, handler) #> env: [frame 0x36dde10] #> #> [[32]] #> <frame 6> (5) #> expr: tryCatchOne(expr, names, parentenv, handlers[[1L]]) #> env: [frame 0x36de158] #> #> [[33]] #> <frame 5> (2) #> expr: tryCatchList(expr, names[-nh], parentenv, handlers[-nh]) #> env: [frame 0x36da6e0] #> #> [[34]] #> <frame 4> (3) #> expr: doTryCatch(return(expr), name, parentenv, handler) #> env: [frame 0x36dac90] #> #> [[35]] #> <frame 3> (2) #> expr: tryCatchOne(tryCatchList(expr, names[-nh], parentenv, handlers[-nh]), <...> #> env: [frame 0x36dafd8] #> #> [[36]] #> <frame 2> (1) #> expr: tryCatchList(expr, classes, parentenv, handlers) #> env: [frame 0x36db320] #> #> [[37]] #> <frame 1> (0) #> expr: tryCatch(withCallingHandlers({ <...> #> env: [frame 0x36dba90] #> #> [[38]] #> <frame 0> [global] #> expr: NULL #> env: [global] #> #> attr(,"class") #> [1] "ctxt_stack" "stack"
# While closures do: identity(identity(ctxt_stack()))
#> [[1]] #> <frame 39> (37) #> expr: identity(ctxt_stack()) #> env: [local 0x21fb478] #> #> [[2]] #> <frame 38> (37) #> expr: identity(identity(ctxt_stack())) #> env: [local 0x21faf70] #> #> [[3]] #> <frame 37> (36) #> expr: eval(expr, envir, enclos) #> env: [local 0x5e9c150] #> #> [[4]] #> <frame 36> (26) #> expr: eval(expr, envir, enclos) #> env: [local 0x21fad40] #> #> [[5]] #> <frame 35> (26) #> expr: withVisible(eval(expr, envir, enclos)) #> env: [local 0x21fa9f8] #> #> [[6]] #> <frame 34> (26) #> expr: withCallingHandlers(withVisible(eval(expr, envir, enclos)), warning = wHandler, <...> #> env: [local 0x220fea8] #> #> [[7]] #> <frame 33> (32) #> expr: doTryCatch(return(expr), name, parentenv, handler) #> env: [local 0x220f540] #> #> [[8]] #> <frame 32> (31) #> expr: tryCatchOne(expr, names, parentenv, handlers[[1L]]) #> env: [local 0x2227760] #> #> [[9]] #> <frame 31> (30) #> expr: tryCatchList(expr, classes, parentenv, handlers) #> env: [local 0x2262df0] #> #> [[10]] #> <frame 30> (29) #> expr: tryCatch(expr, error = function(e) { <...> #> env: [local 0x2269478] #> #> [[11]] #> <frame 29> (28) #> expr: try(f, silent = TRUE) #> env: [local 0x2269210] #> #> [[12]] #> <frame 28> (26) #> expr: handle(ev <- withCallingHandlers(withVisible(eval(expr, envir, <...> #> env: [local 0x2268f70] #> #> [[13]] #> <frame 27> (26) #> expr: timing_fn(handle(ev <- withCallingHandlers(withVisible(eval(expr, <...> #> env: [local 0x2268e20] #> #> [[14]] #> <frame 26> (25) #> expr: evaluate_call(expr, parsed$src[[i]], envir = envir, enclos = enclos, <...> #> env: [frame 0x23cef58] #> #> [[15]] #> <frame 25> (22) #> expr: evaluate::evaluate(code, env, new_device = TRUE) #> env: [frame 0x7585c18] #> #> [[16]] #> <frame 24> (23) #> expr: force(code) #> env: [frame 0x6d16e58] #> #> [[17]] #> <frame 23> (22) #> expr: withr::with_options(list(crayon.enabled = getOption("crayon.enabled", <...> #> env: [frame 0x7751bf0] #> #> [[18]] #> <frame 22> (21) #> expr: .f(code = .l[[c(1L, 1L)]], run = .l[[c(2L, 1L)]], show = .l[[c(3L, <...> #> env: [frame 0x78a50b8] #> #> [[19]] #> <frame 21> (20) #> expr: purrr::pmap_chr(list(code = code, run = run, show = show), format_example_chunk, <...> #> env: [frame 0x75de710] #> #> [[20]] #> <frame 20> (18) #> expr: as_data.tag_examples(tags$tag_examples[[1]], env = new.env(parent = globalenv()), <...> #> env: [frame 0x79d9630] #> #> [[21]] #> <frame 19> (18) #> expr: as_data(tags$tag_examples[[1]], env = new.env(parent = globalenv()), <...> #> env: [frame 0x79d8c20] #> #> [[22]] #> <frame 18> (17) #> expr: data_reference_topic(topic, pkg, examples = examples, run_dont_run = run_dont_run) #> env: [frame 0x8005468] #> #> [[23]] #> <frame 17> (16) #> expr: .f(.x[[i]], ...) #> env: [frame 0x88c8b90] #> #> [[24]] #> <frame 16> (15) #> expr: purrr::map(topics, build_reference_topic, pkg = pkg, lazy = lazy, <...> #> env: [frame 0x79ae7d0] #> #> [[25]] #> <frame 15> (14) #> expr: build_reference(pkg, lazy = lazy, document = document, examples = examples, <...> #> env: [frame 0x5078448] #> #> [[26]] #> <frame 14> (13) #> expr: build_site_local(pkg = pkg, examples = examples, document = document, <...> #> env: [frame 0x1ebac98] #> #> [[27]] #> <frame 13> (12) #> expr: pkgdown::build_site(...) #> env: [frame 0x1b2ad48] #> #> [[28]] #> <frame 12> (0) #> expr: (function (..., crayon_enabled, crayon_colors, pkgdown_internet) <...> #> env: [frame 0x36f02d0] #> #> [[29]] #> <frame 11> (0) #> expr: (function (what, args, quote = FALSE, envir = parent.frame()) <...> #> env: [frame 0x36f1290] #> #> [[30]] #> <frame 10> (0) #> expr: do.call(do.call, c(readRDS("/tmp/RtmpnyPeIi/file43227a57ff01"), <...> #> env: [frame 0x36e10f0] #> #> [[31]] #> <frame 9> (0) #> expr: saveRDS(do.call(do.call, c(readRDS("/tmp/RtmpnyPeIi/file43227a57ff01"), <...> #> env: [frame 0x36e1e80] #> #> [[32]] #> <frame 8> (0) #> expr: withCallingHandlers({ <...> #> env: [frame 0x36dcc58] #> #> [[33]] #> <frame 7> (6) #> expr: doTryCatch(return(expr), name, parentenv, handler) #> env: [frame 0x36dde10] #> #> [[34]] #> <frame 6> (5) #> expr: tryCatchOne(expr, names, parentenv, handlers[[1L]]) #> env: [frame 0x36de158] #> #> [[35]] #> <frame 5> (2) #> expr: tryCatchList(expr, names[-nh], parentenv, handlers[-nh]) #> env: [frame 0x36da6e0] #> #> [[36]] #> <frame 4> (3) #> expr: doTryCatch(return(expr), name, parentenv, handler) #> env: [frame 0x36dac90] #> #> [[37]] #> <frame 3> (2) #> expr: tryCatchOne(tryCatchList(expr, names[-nh], parentenv, handlers[-nh]), <...> #> env: [frame 0x36dafd8] #> #> [[38]] #> <frame 2> (1) #> expr: tryCatchList(expr, classes, parentenv, handlers) #> env: [frame 0x36db320] #> #> [[39]] #> <frame 1> (0) #> expr: tryCatch(withCallingHandlers({ <...> #> env: [frame 0x36dba90] #> #> [[40]] #> <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