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
#> [[1]] #> <frame 37> (36) #> expr: eval(expr, envir, enclos) #> env: [local 0x7c60f28] #> #> [[2]] #> <frame 36> (26) #> expr: eval(expr, envir, enclos) #> env: [local 0x80b8fa0] #> #> [[3]] #> <frame 35> (26) #> expr: withVisible(eval(expr, envir, enclos)) #> env: [local 0x80b8d70] #> #> [[4]] #> <frame 34> (26) #> expr: withCallingHandlers(withVisible(eval(expr, envir, enclos)), warning = wHandler, <...> #> env: [local 0x7ff1140] #> #> [[5]] #> <frame 33> (32) #> expr: doTryCatch(return(expr), name, parentenv, handler) #> env: [local 0x7ff0bc8] #> #> [[6]] #> <frame 32> (31) #> expr: tryCatchOne(expr, names, parentenv, handlers[[1L]]) #> env: [local 0x7ff0880] #> #> [[7]] #> <frame 31> (30) #> expr: tryCatchList(expr, classes, parentenv, handlers) #> env: [local 0x7ff0538] #> #> [[8]] #> <frame 30> (29) #> expr: tryCatch(expr, error = function(e) { <...> #> env: [local 0x7fefe70] #> #> [[9]] #> <frame 29> (28) #> expr: try(f, silent = TRUE) #> env: [local 0x7fefc40] #> #> [[10]] #> <frame 28> (26) #> expr: handle(ev <- withCallingHandlers(withVisible(eval(expr, envir, <...> #> env: [local 0x7fefab8] #> #> [[11]] #> <frame 27> (26) #> expr: timing_fn(handle(ev <- withCallingHandlers(withVisible(eval(expr, <...> #> env: [local 0x7fef9d8] #> #> [[12]] #> <frame 26> (25) #> expr: evaluate_call(expr, parsed$src[[i]], envir = envir, enclos = enclos, <...> #> env: [frame 0x7de0400] #> #> [[13]] #> <frame 25> (22) #> expr: evaluate::evaluate(code, env, new_device = TRUE) #> env: [frame 0x9973b28] #> #> [[14]] #> <frame 24> (23) #> expr: force(code) #> env: [frame 0x996f4d0] #> #> [[15]] #> <frame 23> (22) #> expr: withr::with_options(list(crayon.enabled = getOption("crayon.enabled", <...> #> env: [frame 0x996c9a8] #> #> [[16]] #> <frame 22> (21) #> expr: .f(code = .l[[1L]][[1L]], run = .l[[2L]][[1L]], show = .l[[3L]][[1L]], <...> #> env: [frame 0x996dea8] #> #> [[17]] #> <frame 21> (20) #> expr: purrr::pmap_chr(list(code = code, run = run, show = show), format_example_chunk, <...> #> env: [frame 0x99691c0] #> #> [[18]] #> <frame 20> (18) #> expr: as_data.tag_examples(tags$tag_examples[[1]], env = new.env(parent = globalenv()), <...> #> env: [frame 0x98fa368] #> #> [[19]] #> <frame 19> (18) #> expr: as_data(tags$tag_examples[[1]], env = new.env(parent = globalenv()), <...> #> env: [frame 0x98fa950] #> #> [[20]] #> <frame 18> (17) #> expr: data_reference_topic(topic, pkg, examples = examples, run_dont_run = run_dont_run) #> env: [frame 0x95e3d58] #> #> [[21]] #> <frame 17> (16) #> expr: .f(.x[[i]], ...) #> env: [frame 0x9565948] #> #> [[22]] #> <frame 16> (15) #> expr: purrr::map(topics, build_reference_topic, pkg = pkg, lazy = lazy, <...> #> env: [frame 0x16317f0] #> #> [[23]] #> <frame 15> (14) #> expr: build_reference(pkg, lazy = lazy, document = document, examples = examples, <...> #> env: [frame 0xfc66a8] #> #> [[24]] #> <frame 14> (13) #> expr: build_site_local(pkg = pkg, examples = examples, document = document, <...> #> env: [frame 0x1b3b0b8] #> #> [[25]] #> <frame 13> (12) #> expr: pkgdown::build_site(...) #> env: [frame 0x1b41880] #> #> [[26]] #> <frame 12> (0) #> expr: (function (..., crayon_enabled, crayon_colors, pkgdown_internet) <...> #> env: [frame 0x2c81510] #> #> [[27]] #> <frame 11> (0) #> expr: (function (what, args, quote = FALSE, envir = parent.frame()) <...> #> env: [frame 0x2c8f6d0] #> #> [[28]] #> <frame 10> (0) #> expr: do.call(do.call, c(readRDS("/tmp/RtmpdklTTr/file4ec11733c89d"), <...> #> env: [frame 0x2c7c470] #> #> [[29]] #> <frame 9> (0) #> expr: saveRDS(do.call(do.call, c(readRDS("/tmp/RtmpdklTTr/file4ec11733c89d"), <...> #> env: [frame 0x2c7c7f0] #> #> [[30]] #> <frame 8> (0) #> expr: withCallingHandlers({ <...> #> env: [frame 0x2c77538] #> #> [[31]] #> <frame 7> (6) #> expr: doTryCatch(return(expr), name, parentenv, handler) #> env: [frame 0x2c73d98] #> #> [[32]] #> <frame 6> (5) #> expr: tryCatchOne(expr, names, parentenv, handlers[[1L]]) #> env: [frame 0x2c740e0] #> #> [[33]] #> <frame 5> (2) #> expr: tryCatchList(expr, names[-nh], parentenv, handlers[-nh]) #> env: [frame 0x2c74498] #> #> [[34]] #> <frame 4> (3) #> expr: doTryCatch(return(expr), name, parentenv, handler) #> env: [frame 0x2c74a48] #> #> [[35]] #> <frame 3> (2) #> expr: tryCatchOne(tryCatchList(expr, names[-nh], parentenv, handlers[-nh]), <...> #> env: [frame 0x2c74d90] #> #> [[36]] #> <frame 2> (1) #> expr: tryCatchList(expr, classes, parentenv, handlers) #> env: [frame 0x2c750d8] #> #> [[37]] #> <frame 1> (0) #> expr: tryCatch(withCallingHandlers({ <...> #> env: [frame 0x2c75810] #> #> [[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 0x81f68a8] #> #> [[2]] #> <frame 38> (37) #> expr: identity(identity(ctxt_stack())) #> env: [local 0x81f6790] #> #> [[3]] #> <frame 37> (36) #> expr: eval(expr, envir, enclos) #> env: [local 0x7c60f28] #> #> [[4]] #> <frame 36> (26) #> expr: eval(expr, envir, enclos) #> env: [local 0x81f65d0] #> #> [[5]] #> <frame 35> (26) #> expr: withVisible(eval(expr, envir, enclos)) #> env: [local 0x81f63a0] #> #> [[6]] #> <frame 34> (26) #> expr: withCallingHandlers(withVisible(eval(expr, envir, enclos)), warning = wHandler, <...> #> env: [local 0x7235290] #> #> [[7]] #> <frame 33> (32) #> expr: doTryCatch(return(expr), name, parentenv, handler) #> env: [local 0x7234490] #> #> [[8]] #> <frame 32> (31) #> expr: tryCatchOne(expr, names, parentenv, handlers[[1L]]) #> env: [local 0x7234148] #> #> [[9]] #> <frame 31> (30) #> expr: tryCatchList(expr, classes, parentenv, handlers) #> env: [local 0x7233dc8] #> #> [[10]] #> <frame 30> (29) #> expr: tryCatch(expr, error = function(e) { <...> #> env: [local 0x72336c8] #> #> [[11]] #> <frame 29> (28) #> expr: try(f, silent = TRUE) #> env: [local 0x793c860] #> #> [[12]] #> <frame 28> (26) #> expr: handle(ev <- withCallingHandlers(withVisible(eval(expr, envir, <...> #> env: [local 0x793c6d8] #> #> [[13]] #> <frame 27> (26) #> expr: timing_fn(handle(ev <- withCallingHandlers(withVisible(eval(expr, <...> #> env: [local 0x793c5f8] #> #> [[14]] #> <frame 26> (25) #> expr: evaluate_call(expr, parsed$src[[i]], envir = envir, enclos = enclos, <...> #> env: [frame 0x79026e8] #> #> [[15]] #> <frame 25> (22) #> expr: evaluate::evaluate(code, env, new_device = TRUE) #> env: [frame 0x9973b28] #> #> [[16]] #> <frame 24> (23) #> expr: force(code) #> env: [frame 0x996f4d0] #> #> [[17]] #> <frame 23> (22) #> expr: withr::with_options(list(crayon.enabled = getOption("crayon.enabled", <...> #> env: [frame 0x996c9a8] #> #> [[18]] #> <frame 22> (21) #> expr: .f(code = .l[[1L]][[1L]], run = .l[[2L]][[1L]], show = .l[[3L]][[1L]], <...> #> env: [frame 0x996dea8] #> #> [[19]] #> <frame 21> (20) #> expr: purrr::pmap_chr(list(code = code, run = run, show = show), format_example_chunk, <...> #> env: [frame 0x99691c0] #> #> [[20]] #> <frame 20> (18) #> expr: as_data.tag_examples(tags$tag_examples[[1]], env = new.env(parent = globalenv()), <...> #> env: [frame 0x98fa368] #> #> [[21]] #> <frame 19> (18) #> expr: as_data(tags$tag_examples[[1]], env = new.env(parent = globalenv()), <...> #> env: [frame 0x98fa950] #> #> [[22]] #> <frame 18> (17) #> expr: data_reference_topic(topic, pkg, examples = examples, run_dont_run = run_dont_run) #> env: [frame 0x95e3d58] #> #> [[23]] #> <frame 17> (16) #> expr: .f(.x[[i]], ...) #> env: [frame 0x9565948] #> #> [[24]] #> <frame 16> (15) #> expr: purrr::map(topics, build_reference_topic, pkg = pkg, lazy = lazy, <...> #> env: [frame 0x16317f0] #> #> [[25]] #> <frame 15> (14) #> expr: build_reference(pkg, lazy = lazy, document = document, examples = examples, <...> #> env: [frame 0xfc66a8] #> #> [[26]] #> <frame 14> (13) #> expr: build_site_local(pkg = pkg, examples = examples, document = document, <...> #> env: [frame 0x1b3b0b8] #> #> [[27]] #> <frame 13> (12) #> expr: pkgdown::build_site(...) #> env: [frame 0x1b41880] #> #> [[28]] #> <frame 12> (0) #> expr: (function (..., crayon_enabled, crayon_colors, pkgdown_internet) <...> #> env: [frame 0x2c81510] #> #> [[29]] #> <frame 11> (0) #> expr: (function (what, args, quote = FALSE, envir = parent.frame()) <...> #> env: [frame 0x2c8f6d0] #> #> [[30]] #> <frame 10> (0) #> expr: do.call(do.call, c(readRDS("/tmp/RtmpdklTTr/file4ec11733c89d"), <...> #> env: [frame 0x2c7c470] #> #> [[31]] #> <frame 9> (0) #> expr: saveRDS(do.call(do.call, c(readRDS("/tmp/RtmpdklTTr/file4ec11733c89d"), <...> #> env: [frame 0x2c7c7f0] #> #> [[32]] #> <frame 8> (0) #> expr: withCallingHandlers({ <...> #> env: [frame 0x2c77538] #> #> [[33]] #> <frame 7> (6) #> expr: doTryCatch(return(expr), name, parentenv, handler) #> env: [frame 0x2c73d98] #> #> [[34]] #> <frame 6> (5) #> expr: tryCatchOne(expr, names, parentenv, handlers[[1L]]) #> env: [frame 0x2c740e0] #> #> [[35]] #> <frame 5> (2) #> expr: tryCatchList(expr, names[-nh], parentenv, handlers[-nh]) #> env: [frame 0x2c74498] #> #> [[36]] #> <frame 4> (3) #> expr: doTryCatch(return(expr), name, parentenv, handler) #> env: [frame 0x2c74a48] #> #> [[37]] #> <frame 3> (2) #> expr: tryCatchOne(tryCatchList(expr, names[-nh], parentenv, handlers[-nh]), <...> #> env: [frame 0x2c74d90] #> #> [[38]] #> <frame 2> (1) #> expr: tryCatchList(expr, classes, parentenv, handlers) #> env: [frame 0x2c750d8] #> #> [[39]] #> <frame 1> (0) #> expr: tryCatch(withCallingHandlers({ <...> #> env: [frame 0x2c75810] #> #> [[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