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)
| x | Object to be tested. |
|---|
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.
#> [1] FALSE#> [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#> [1] TRUE#> [1] TRUE# Primitive functions never appear in evaluation stacks: is_primitive(base::`[[`)#> [1] TRUE#> [1] TRUE#> [[1]] #> <frame 33> (32) #> expr: eval(expr, envir, enclos) #> env: [local 0x55b50ebbab30] #> #> [[2]] #> <frame 32> (22) #> expr: eval(expr, envir, enclos) #> env: [local 0x55b50c586058] #> #> [[3]] #> <frame 31> (22) #> expr: withVisible(eval(expr, envir, enclos)) #> env: [local 0x55b50c586288] #> #> [[4]] #> <frame 30> (22) #> expr: withCallingHandlers(withVisible(eval(expr, envir, enclos)), warning = wHandler, <...> #> env: [local 0x55b50c586838] #> #> [[5]] #> <frame 29> (28) #> expr: doTryCatch(return(expr), name, parentenv, handler) #> env: [local 0x55b50c586db0] #> #> [[6]] #> <frame 28> (27) #> expr: tryCatchOne(expr, names, parentenv, handlers[[1L]]) #> env: [local 0x55b50c5870f8] #> #> [[7]] #> <frame 27> (26) #> expr: tryCatchList(expr, classes, parentenv, handlers) #> env: [local 0x55b50c587440] #> #> [[8]] #> <frame 26> (25) #> expr: tryCatch(expr, error = function(e) { <...> #> env: [local 0x55b50c583cd8] #> #> [[9]] #> <frame 25> (24) #> expr: try(f, silent = TRUE) #> env: [local 0x55b50c583f08] #> #> [[10]] #> <frame 24> (22) #> expr: handle(ev <- withCallingHandlers(withVisible(eval(expr, envir, <...> #> env: [local 0x55b50c584090] #> #> [[11]] #> <frame 23> (22) #> expr: timing_fn(handle(ev <- withCallingHandlers(withVisible(eval(expr, <...> #> env: [local 0x55b50c584170] #> #> [[12]] #> <frame 22> (21) #> expr: evaluate_call(expr, parsed$src[[i]], envir = envir, enclos = enclos, <...> #> env: [frame 0x55b50c572d40] #> #> [[13]] #> <frame 21> (20) #> expr: evaluate::evaluate(x, child_env(env), new_device = TRUE) #> env: [frame 0x55b50f09f270] #> #> [[14]] #> <frame 20> (19) #> expr: highlight_examples(code, topic, env = env) #> env: [frame 0x55b50f0932e0] #> #> [[15]] #> <frame 19> (18) #> expr: run_examples(tags$tag_examples[[1]], env = new.env(parent = globalenv()), <...> #> env: [frame 0x55b50f071228] #> #> [[16]] #> <frame 18> (17) #> expr: data_reference_topic(topic, pkg, examples = examples, run_dont_run = run_dont_run) #> env: [frame 0x55b50d6135e0] #> #> [[17]] #> <frame 17> (16) #> expr: .f(.x[[i]], ...) #> env: [frame 0x55b50d579988] #> #> [[18]] #> <frame 16> (15) #> expr: purrr::map(topics, build_reference_topic, pkg = pkg, lazy = lazy, <...> #> env: [frame 0x55b50043f718] #> #> [[19]] #> <frame 15> (14) #> expr: build_reference(pkg, lazy = lazy, examples = examples, run_dont_run = run_dont_run, <...> #> env: [frame 0x55b501caf378] #> #> [[20]] #> <frame 14> (13) #> expr: build_site_local(pkg = pkg, examples = examples, run_dont_run = run_dont_run, <...> #> env: [frame 0x55b4feecce58] #> #> [[21]] #> <frame 13> (12) #> expr: pkgdown::build_site(...) #> env: [frame 0x55b4ff1089b0] #> #> [[22]] #> <frame 12> (0) #> expr: (function (..., crayon_enabled, crayon_colors, pkgdown_internet) <...> #> env: [frame 0x55b4ffc68298] #> #> [[23]] #> <frame 11> (0) #> expr: (function (what, args, quote = FALSE, envir = parent.frame()) <...> #> env: [frame 0x55b4ffc66bd8] #> #> [[24]] #> <frame 10> (0) #> expr: do.call(do.call, c(readRDS("/tmp/Rtmp7yGmwI/callr-fun-7bcd6bbce04b"), <...> #> env: [frame 0x55b4ffc64650] #> #> [[25]] #> <frame 9> (0) #> expr: saveRDS(do.call(do.call, c(readRDS("/tmp/Rtmp7yGmwI/callr-fun-7bcd6bbce04b"), <...> #> env: [frame 0x55b4ffc60ba0] #> #> [[26]] #> <frame 8> (0) #> expr: withCallingHandlers({ <...> #> env: [frame 0x55b4ffc613f0] #> #> [[27]] #> <frame 7> (6) #> expr: doTryCatch(return(expr), name, parentenv, handler) #> env: [frame 0x55b4ffc61a80] #> #> [[28]] #> <frame 6> (5) #> expr: tryCatchOne(expr, names, parentenv, handlers[[1L]]) #> env: [frame 0x55b4ffc61dc8] #> #> [[29]] #> <frame 5> (2) #> expr: tryCatchList(expr, names[-nh], parentenv, handlers[-nh]) #> env: [frame 0x55b4ffc62180] #> #> [[30]] #> <frame 4> (3) #> expr: doTryCatch(return(expr), name, parentenv, handler) #> env: [frame 0x55b4ffc62730] #> #> [[31]] #> <frame 3> (2) #> expr: tryCatchOne(tryCatchList(expr, names[-nh], parentenv, handlers[-nh]), <...> #> env: [frame 0x55b4ffc5cd28] #> #> [[32]] #> <frame 2> (1) #> expr: tryCatchList(expr, classes, parentenv, handlers) #> env: [frame 0x55b4ffc5d070] #> #> [[33]] #> <frame 1> (0) #> expr: tryCatch(withCallingHandlers({ <...> #> env: [frame 0x55b4ffc5d7a8] #> #> [[34]] #> <frame 0> [global] #> expr: NULL #> env: [global] #> #> attr(,"class") #> [1] "ctxt_stack" "stack"#> [[1]] #> <frame 35> (33) #> expr: identity(ctxt_stack()) #> env: [local 0x55b50c8f66f0] #> #> [[2]] #> <frame 34> (33) #> expr: identity(identity(ctxt_stack())) #> env: [local 0x55b50c8f6808] #> #> [[3]] #> <frame 33> (32) #> expr: eval(expr, envir, enclos) #> env: [local 0x55b50ebbab30] #> #> [[4]] #> <frame 32> (22) #> expr: eval(expr, envir, enclos) #> env: [local 0x55b50c8f69c8] #> #> [[5]] #> <frame 31> (22) #> expr: withVisible(eval(expr, envir, enclos)) #> env: [local 0x55b50c8f6bf8] #> #> [[6]] #> <frame 30> (22) #> expr: withCallingHandlers(withVisible(eval(expr, envir, enclos)), warning = wHandler, <...> #> env: [local 0x55b50c8f71a8] #> #> [[7]] #> <frame 29> (28) #> expr: doTryCatch(return(expr), name, parentenv, handler) #> env: [local 0x55b50c8f7720] #> #> [[8]] #> <frame 28> (27) #> expr: tryCatchOne(expr, names, parentenv, handlers[[1L]]) #> env: [local 0x55b50c8f7a68] #> #> [[9]] #> <frame 27> (26) #> expr: tryCatchList(expr, classes, parentenv, handlers) #> env: [local 0x55b50c8f7db0] #> #> [[10]] #> <frame 26> (25) #> expr: tryCatch(expr, error = function(e) { <...> #> env: [local 0x55b50c8f4648] #> #> [[11]] #> <frame 25> (24) #> expr: try(f, silent = TRUE) #> env: [local 0x55b50c8f4878] #> #> [[12]] #> <frame 24> (22) #> expr: handle(ev <- withCallingHandlers(withVisible(eval(expr, envir, <...> #> env: [local 0x55b50c8f4a00] #> #> [[13]] #> <frame 23> (22) #> expr: timing_fn(handle(ev <- withCallingHandlers(withVisible(eval(expr, <...> #> env: [local 0x55b50c8f4ae0] #> #> [[14]] #> <frame 22> (21) #> expr: evaluate_call(expr, parsed$src[[i]], envir = envir, enclos = enclos, <...> #> env: [frame 0x55b50c8e5918] #> #> [[15]] #> <frame 21> (20) #> expr: evaluate::evaluate(x, child_env(env), new_device = TRUE) #> env: [frame 0x55b50f09f270] #> #> [[16]] #> <frame 20> (19) #> expr: highlight_examples(code, topic, env = env) #> env: [frame 0x55b50f0932e0] #> #> [[17]] #> <frame 19> (18) #> expr: run_examples(tags$tag_examples[[1]], env = new.env(parent = globalenv()), <...> #> env: [frame 0x55b50f071228] #> #> [[18]] #> <frame 18> (17) #> expr: data_reference_topic(topic, pkg, examples = examples, run_dont_run = run_dont_run) #> env: [frame 0x55b50d6135e0] #> #> [[19]] #> <frame 17> (16) #> expr: .f(.x[[i]], ...) #> env: [frame 0x55b50d579988] #> #> [[20]] #> <frame 16> (15) #> expr: purrr::map(topics, build_reference_topic, pkg = pkg, lazy = lazy, <...> #> env: [frame 0x55b50043f718] #> #> [[21]] #> <frame 15> (14) #> expr: build_reference(pkg, lazy = lazy, examples = examples, run_dont_run = run_dont_run, <...> #> env: [frame 0x55b501caf378] #> #> [[22]] #> <frame 14> (13) #> expr: build_site_local(pkg = pkg, examples = examples, run_dont_run = run_dont_run, <...> #> env: [frame 0x55b4feecce58] #> #> [[23]] #> <frame 13> (12) #> expr: pkgdown::build_site(...) #> env: [frame 0x55b4ff1089b0] #> #> [[24]] #> <frame 12> (0) #> expr: (function (..., crayon_enabled, crayon_colors, pkgdown_internet) <...> #> env: [frame 0x55b4ffc68298] #> #> [[25]] #> <frame 11> (0) #> expr: (function (what, args, quote = FALSE, envir = parent.frame()) <...> #> env: [frame 0x55b4ffc66bd8] #> #> [[26]] #> <frame 10> (0) #> expr: do.call(do.call, c(readRDS("/tmp/Rtmp7yGmwI/callr-fun-7bcd6bbce04b"), <...> #> env: [frame 0x55b4ffc64650] #> #> [[27]] #> <frame 9> (0) #> expr: saveRDS(do.call(do.call, c(readRDS("/tmp/Rtmp7yGmwI/callr-fun-7bcd6bbce04b"), <...> #> env: [frame 0x55b4ffc60ba0] #> #> [[28]] #> <frame 8> (0) #> expr: withCallingHandlers({ <...> #> env: [frame 0x55b4ffc613f0] #> #> [[29]] #> <frame 7> (6) #> expr: doTryCatch(return(expr), name, parentenv, handler) #> env: [frame 0x55b4ffc61a80] #> #> [[30]] #> <frame 6> (5) #> expr: tryCatchOne(expr, names, parentenv, handlers[[1L]]) #> env: [frame 0x55b4ffc61dc8] #> #> [[31]] #> <frame 5> (2) #> expr: tryCatchList(expr, names[-nh], parentenv, handlers[-nh]) #> env: [frame 0x55b4ffc62180] #> #> [[32]] #> <frame 4> (3) #> expr: doTryCatch(return(expr), name, parentenv, handler) #> env: [frame 0x55b4ffc62730] #> #> [[33]] #> <frame 3> (2) #> expr: tryCatchOne(tryCatchList(expr, names[-nh], parentenv, handlers[-nh]), <...> #> env: [frame 0x55b4ffc5cd28] #> #> [[34]] #> <frame 2> (1) #> expr: tryCatchList(expr, classes, parentenv, handlers) #> env: [frame 0x55b4ffc5d070] #> #> [[35]] #> <frame 1> (0) #> expr: tryCatch(withCallingHandlers({ <...> #> env: [frame 0x55b4ffc5d7a8] #> #> [[36]] #> <frame 0> [global] #> expr: NULL #> env: [global] #> #> attr(,"class") #> [1] "ctxt_stack" "stack"#> [1] TRUE#> [1] TRUEis_primitive_eager(base::`+`)#> [1] TRUE# However, primitives that operate on expressions, like quote() or # substitute(), are lazy: is_primitive_lazy(base::quote)#> [1] TRUE#> [1] TRUE