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 0x838c0b8] #> #> [[2]] #> <frame 36> (26) #> expr: eval(expr, envir, enclos) #> env: [local 0x76cce40] #> #> [[3]] #> <frame 35> (26) #> expr: withVisible(eval(expr, envir, enclos)) #> env: [local 0x76ccba0] #> #> [[4]] #> <frame 34> (26) #> expr: withCallingHandlers(withVisible(eval(expr, envir, enclos)), warning = wHandler, <...> #> env: [local 0x76cc5b8] #> #> [[5]] #> <frame 33> (32) #> expr: doTryCatch(return(expr), name, parentenv, handler) #> env: [local 0x76cfc08] #> #> [[6]] #> <frame 32> (31) #> expr: tryCatchOne(expr, names, parentenv, handlers[[1L]]) #> env: [local 0x76cf888] #> #> [[7]] #> <frame 31> (30) #> expr: tryCatchList(expr, classes, parentenv, handlers) #> env: [local 0x76cf460] #> #> [[8]] #> <frame 30> (29) #> expr: tryCatch(expr, error = function(e) { <...> #> env: [local 0x76ced28] #> #> [[9]] #> <frame 29> (28) #> expr: try(f, silent = TRUE) #> env: [local 0x76ceac0] #> #> [[10]] #> <frame 28> (26) #> expr: handle(ev <- withCallingHandlers(withVisible(eval(expr, envir, <...> #> env: [local 0x76ce890] #> #> [[11]] #> <frame 27> (26) #> expr: timing_fn(handle(ev <- withCallingHandlers(withVisible(eval(expr, <...> #> env: [local 0x76ce7b0] #> #> [[12]] #> <frame 26> (25) #> expr: evaluate_call(expr, parsed$src[[i]], envir = envir, enclos = enclos, <...> #> env: [frame 0x76e3ac8] #> #> [[13]] #> <frame 25> (22) #> expr: evaluate::evaluate(code, env, new_device = TRUE) #> env: [frame 0x74f40a0] #> #> [[14]] #> <frame 24> (23) #> expr: force(code) #> env: [frame 0x6839c20] #> #> [[15]] #> <frame 23> (22) #> expr: withr::with_options(list(crayon.enabled = getOption("crayon.enabled", <...> #> env: [frame 0x6838288] #> #> [[16]] #> <frame 22> (21) #> expr: .f(code = .l[[1L]][[1L]], run = .l[[2L]][[1L]], show = .l[[3L]][[1L]], <...> #> env: [frame 0x7d4d800] #> #> [[17]] #> <frame 21> (20) #> expr: purrr::pmap_chr(list(code = code, run = run, show = show), format_example_chunk, <...> #> env: [frame 0x739fab0] #> #> [[18]] #> <frame 20> (18) #> expr: as_data.tag_examples(tags$tag_examples[[1]], env = new.env(parent = globalenv()), <...> #> env: [frame 0x8052f28] #> #> [[19]] #> <frame 19> (18) #> expr: as_data(tags$tag_examples[[1]], env = new.env(parent = globalenv()), <...> #> env: [frame 0x8052518] #> #> [[20]] #> <frame 18> (17) #> expr: data_reference_topic(topic, pkg, examples = examples, run_dont_run = run_dont_run) #> env: [frame 0x8a83320] #> #> [[21]] #> <frame 17> (16) #> expr: .f(.x[[i]], ...) #> env: [frame 0x81835a0] #> #> [[22]] #> <frame 16> (15) #> expr: purrr::map(topics, build_reference_topic, pkg = pkg, lazy = lazy, <...> #> env: [frame 0x48b2d18] #> #> [[23]] #> <frame 15> (14) #> expr: build_reference(pkg, lazy = lazy, document = document, examples = examples, <...> #> env: [frame 0x4bdc4d8] #> #> [[24]] #> <frame 14> (13) #> expr: build_site_local(pkg = pkg, examples = examples, document = document, <...> #> env: [frame 0x19009a0] #> #> [[25]] #> <frame 13> (12) #> expr: pkgdown::build_site(...) #> env: [frame 0x19cd388] #> #> [[26]] #> <frame 12> (0) #> expr: (function (..., crayon_enabled, crayon_colors, pkgdown_internet) <...> #> env: [frame 0x321df80] #> #> [[27]] #> <frame 11> (0) #> expr: (function (what, args, quote = FALSE, envir = parent.frame()) <...> #> env: [frame 0x321b110] #> #> [[28]] #> <frame 10> (0) #> expr: do.call(do.call, c(readRDS("/tmp/RtmpMVh6Pm/file4d004ee8fc43"), <...> #> env: [frame 0x3218f50] #> #> [[29]] #> <frame 9> (0) #> expr: saveRDS(do.call(do.call, c(readRDS("/tmp/RtmpMVh6Pm/file4d004ee8fc43"), <...> #> env: [frame 0x3219ce0] #> #> [[30]] #> <frame 8> (0) #> expr: withCallingHandlers({ <...> #> env: [frame 0x32188e8] #> #> [[31]] #> <frame 7> (6) #> expr: doTryCatch(return(expr), name, parentenv, handler) #> env: [frame 0x3215c70] #> #> [[32]] #> <frame 6> (5) #> expr: tryCatchOne(expr, names, parentenv, handlers[[1L]]) #> env: [frame 0x3215fb8] #> #> [[33]] #> <frame 5> (2) #> expr: tryCatchList(expr, names[-nh], parentenv, handlers[-nh]) #> env: [frame 0x3216370] #> #> [[34]] #> <frame 4> (3) #> expr: doTryCatch(return(expr), name, parentenv, handler) #> env: [frame 0x3216920] #> #> [[35]] #> <frame 3> (2) #> expr: tryCatchOne(tryCatchList(expr, names[-nh], parentenv, handlers[-nh]), <...> #> env: [frame 0x3216c68] #> #> [[36]] #> <frame 2> (1) #> expr: tryCatchList(expr, classes, parentenv, handlers) #> env: [frame 0x3213180] #> #> [[37]] #> <frame 1> (0) #> expr: tryCatch(withCallingHandlers({ <...> #> env: [frame 0x32138f0] #> #> [[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 0x5d14830] #> #> [[2]] #> <frame 38> (37) #> expr: identity(identity(ctxt_stack())) #> env: [local 0x5d146e0] #> #> [[3]] #> <frame 37> (36) #> expr: eval(expr, envir, enclos) #> env: [local 0x838c0b8] #> #> [[4]] #> <frame 36> (26) #> expr: eval(expr, envir, enclos) #> env: [local 0x5d1b448] #> #> [[5]] #> <frame 35> (26) #> expr: withVisible(eval(expr, envir, enclos)) #> env: [local 0x5d2a280] #> #> [[6]] #> <frame 34> (26) #> expr: withCallingHandlers(withVisible(eval(expr, envir, enclos)), warning = wHandler, <...> #> env: [local 0x5d2aae0] #> #> [[7]] #> <frame 33> (32) #> expr: doTryCatch(return(expr), name, parentenv, handler) #> env: [local 0x5d36bf8] #> #> [[8]] #> <frame 32> (31) #> expr: tryCatchOne(expr, names, parentenv, handlers[[1L]]) #> env: [local 0x5d3b9f8] #> #> [[9]] #> <frame 31> (30) #> expr: tryCatchList(expr, classes, parentenv, handlers) #> env: [local 0x5d3aaa8] #> #> [[10]] #> <frame 30> (29) #> expr: tryCatch(expr, error = function(e) { <...> #> env: [local 0x5d3d1a8] #> #> [[11]] #> <frame 29> (28) #> expr: try(f, silent = TRUE) #> env: [local 0x5d3ca00] #> #> [[12]] #> <frame 28> (26) #> expr: handle(ev <- withCallingHandlers(withVisible(eval(expr, envir, <...> #> env: [local 0x5d3c878] #> #> [[13]] #> <frame 27> (26) #> expr: timing_fn(handle(ev <- withCallingHandlers(withVisible(eval(expr, <...> #> env: [local 0x5d3c2c8] #> #> [[14]] #> <frame 26> (25) #> expr: evaluate_call(expr, parsed$src[[i]], envir = envir, enclos = enclos, <...> #> env: [frame 0x5e60060] #> #> [[15]] #> <frame 25> (22) #> expr: evaluate::evaluate(code, env, new_device = TRUE) #> env: [frame 0x74f40a0] #> #> [[16]] #> <frame 24> (23) #> expr: force(code) #> env: [frame 0x6839c20] #> #> [[17]] #> <frame 23> (22) #> expr: withr::with_options(list(crayon.enabled = getOption("crayon.enabled", <...> #> env: [frame 0x6838288] #> #> [[18]] #> <frame 22> (21) #> expr: .f(code = .l[[1L]][[1L]], run = .l[[2L]][[1L]], show = .l[[3L]][[1L]], <...> #> env: [frame 0x7d4d800] #> #> [[19]] #> <frame 21> (20) #> expr: purrr::pmap_chr(list(code = code, run = run, show = show), format_example_chunk, <...> #> env: [frame 0x739fab0] #> #> [[20]] #> <frame 20> (18) #> expr: as_data.tag_examples(tags$tag_examples[[1]], env = new.env(parent = globalenv()), <...> #> env: [frame 0x8052f28] #> #> [[21]] #> <frame 19> (18) #> expr: as_data(tags$tag_examples[[1]], env = new.env(parent = globalenv()), <...> #> env: [frame 0x8052518] #> #> [[22]] #> <frame 18> (17) #> expr: data_reference_topic(topic, pkg, examples = examples, run_dont_run = run_dont_run) #> env: [frame 0x8a83320] #> #> [[23]] #> <frame 17> (16) #> expr: .f(.x[[i]], ...) #> env: [frame 0x81835a0] #> #> [[24]] #> <frame 16> (15) #> expr: purrr::map(topics, build_reference_topic, pkg = pkg, lazy = lazy, <...> #> env: [frame 0x48b2d18] #> #> [[25]] #> <frame 15> (14) #> expr: build_reference(pkg, lazy = lazy, document = document, examples = examples, <...> #> env: [frame 0x4bdc4d8] #> #> [[26]] #> <frame 14> (13) #> expr: build_site_local(pkg = pkg, examples = examples, document = document, <...> #> env: [frame 0x19009a0] #> #> [[27]] #> <frame 13> (12) #> expr: pkgdown::build_site(...) #> env: [frame 0x19cd388] #> #> [[28]] #> <frame 12> (0) #> expr: (function (..., crayon_enabled, crayon_colors, pkgdown_internet) <...> #> env: [frame 0x321df80] #> #> [[29]] #> <frame 11> (0) #> expr: (function (what, args, quote = FALSE, envir = parent.frame()) <...> #> env: [frame 0x321b110] #> #> [[30]] #> <frame 10> (0) #> expr: do.call(do.call, c(readRDS("/tmp/RtmpMVh6Pm/file4d004ee8fc43"), <...> #> env: [frame 0x3218f50] #> #> [[31]] #> <frame 9> (0) #> expr: saveRDS(do.call(do.call, c(readRDS("/tmp/RtmpMVh6Pm/file4d004ee8fc43"), <...> #> env: [frame 0x3219ce0] #> #> [[32]] #> <frame 8> (0) #> expr: withCallingHandlers({ <...> #> env: [frame 0x32188e8] #> #> [[33]] #> <frame 7> (6) #> expr: doTryCatch(return(expr), name, parentenv, handler) #> env: [frame 0x3215c70] #> #> [[34]] #> <frame 6> (5) #> expr: tryCatchOne(expr, names, parentenv, handlers[[1L]]) #> env: [frame 0x3215fb8] #> #> [[35]] #> <frame 5> (2) #> expr: tryCatchList(expr, names[-nh], parentenv, handlers[-nh]) #> env: [frame 0x3216370] #> #> [[36]] #> <frame 4> (3) #> expr: doTryCatch(return(expr), name, parentenv, handler) #> env: [frame 0x3216920] #> #> [[37]] #> <frame 3> (2) #> expr: tryCatchOne(tryCatchList(expr, names[-nh], parentenv, handlers[-nh]), <...> #> env: [frame 0x3216c68] #> #> [[38]] #> <frame 2> (1) #> expr: tryCatchList(expr, classes, parentenv, handlers) #> env: [frame 0x3213180] #> #> [[39]] #> <frame 1> (0) #> expr: tryCatch(withCallingHandlers({ <...> #> env: [frame 0x32138f0] #> #> [[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