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 35> (34) #> expr: eval(expr, envir, enclos) #> env: [local 0x5616eb2f6cc8] #> #> [[2]] #> <frame 34> (24) #> expr: eval(expr, envir, enclos) #> env: [local 0x5616ee0eefc8] #> #> [[3]] #> <frame 33> (24) #> expr: withVisible(eval(expr, envir, enclos)) #> env: [local 0x5616ee0ef1f8] #> #> [[4]] #> <frame 32> (24) #> expr: withCallingHandlers(withVisible(eval(expr, envir, enclos)), warning = wHandler, <...> #> env: [local 0x5616ee0ef7a8] #> #> [[5]] #> <frame 31> (30) #> expr: doTryCatch(return(expr), name, parentenv, handler) #> env: [local 0x5616ee0efd20] #> #> [[6]] #> <frame 30> (29) #> expr: tryCatchOne(expr, names, parentenv, handlers[[1L]]) #> env: [local 0x5616ee0f0068] #> #> [[7]] #> <frame 29> (28) #> expr: tryCatchList(expr, classes, parentenv, handlers) #> env: [local 0x5616ee0f03b0] #> #> [[8]] #> <frame 28> (27) #> expr: tryCatch(expr, error = function(e) { <...> #> env: [local 0x5616ee0ecc80] #> #> [[9]] #> <frame 27> (26) #> expr: try(f, silent = TRUE) #> env: [local 0x5616ee0eceb0] #> #> [[10]] #> <frame 26> (24) #> expr: handle(ev <- withCallingHandlers(withVisible(eval(expr, envir, <...> #> env: [local 0x5616ee0ed038] #> #> [[11]] #> <frame 25> (24) #> expr: timing_fn(handle(ev <- withCallingHandlers(withVisible(eval(expr, <...> #> env: [local 0x5616ee0ed118] #> #> [[12]] #> <frame 24> (23) #> expr: evaluate_call(expr, parsed$src[[i]], envir = envir, enclos = enclos, <...> #> env: [frame 0x5616ee0da120] #> #> [[13]] #> <frame 23> (22) #> expr: evaluate::evaluate(code, child_env(env), new_device = TRUE) #> env: [frame 0x5616ee8153d0] #> #> [[14]] #> <frame 22> (21) #> expr: downlit::evaluate_and_highlight(code, fig_save = fig_save_topic, <...> #> env: [frame 0x5616ee80e090] #> #> [[15]] #> <frame 21> (20) #> expr: highlight_examples(code, topic, env = env) #> env: [frame 0x5616ee805670] #> #> [[16]] #> <frame 20> (19) #> expr: run_examples(tags$tag_examples[[1]], env = new.env(parent = globalenv()), <...> #> env: [frame 0x5616ec34dcb8] #> #> [[17]] #> <frame 19> (17) #> expr: data_reference_topic(topic, pkg, examples = examples, run_dont_run = run_dont_run) #> env: [frame 0x5616eb5431c8] #> #> [[18]] #> <frame 18> (17) #> expr: withCallingHandlers(data_reference_topic(topic, pkg, examples = examples, <...> #> env: [frame 0x5616eb543900] #> #> [[19]] #> <frame 17> (16) #> expr: .f(.x[[i]], ...) #> env: [frame 0x5616eaef8a88] #> #> [[20]] #> <frame 16> (15) #> expr: purrr::map(topics, build_reference_topic, pkg = pkg, lazy = lazy, <...> #> env: [frame 0x5616e726b258] #> #> [[21]] #> <frame 15> (14) #> expr: build_reference(pkg, lazy = lazy, examples = examples, run_dont_run = run_dont_run, <...> #> env: [frame 0x5616e6c5d868] #> #> [[22]] #> <frame 14> (13) #> expr: build_site_local(pkg = pkg, examples = examples, run_dont_run = run_dont_run, <...> #> env: [frame 0x5616e4de4458] #> #> [[23]] #> <frame 13> (12) #> expr: pkgdown::build_site(...) #> env: [frame 0x5616e4da9bc0] #> #> [[24]] #> <frame 12> (0) #> expr: (function (..., crayon_enabled, crayon_colors, pkgdown_internet) <...> #> env: [frame 0x5616e426fef0] #> #> [[25]] #> <frame 11> (0) #> expr: (function (what, args, quote = FALSE, envir = parent.frame()) <...> #> env: [frame 0x5616e426ede0] #> #> [[26]] #> <frame 10> (0) #> expr: do.call(do.call, c(readRDS("/tmp/RtmpJYaP2e/callr-fun-7b2c52a64aa5"), <...> #> env: [frame 0x5616e49e25a8] #> #> [[27]] #> <frame 9> (0) #> expr: saveRDS(do.call(do.call, c(readRDS("/tmp/RtmpJYaP2e/callr-fun-7b2c52a64aa5"), <...> #> env: [frame 0x5616e49e2928] #> #> [[28]] #> <frame 8> (0) #> expr: withCallingHandlers({ <...> #> env: [frame 0x5616e49df348] #> #> [[29]] #> <frame 7> (6) #> expr: doTryCatch(return(expr), name, parentenv, handler) #> env: [frame 0x5616e49df9d8] #> #> [[30]] #> <frame 6> (5) #> expr: tryCatchOne(expr, names, parentenv, handlers[[1L]]) #> env: [frame 0x5616e49dfd20] #> #> [[31]] #> <frame 5> (2) #> expr: tryCatchList(expr, names[-nh], parentenv, handlers[-nh]) #> env: [frame 0x5616e49e00d8] #> #> [[32]] #> <frame 4> (3) #> expr: doTryCatch(return(expr), name, parentenv, handler) #> env: [frame 0x5616e49e0688] #> #> [[33]] #> <frame 3> (2) #> expr: tryCatchOne(tryCatchList(expr, names[-nh], parentenv, handlers[-nh]), <...> #> env: [frame 0x5616e49e09d0] #> #> [[34]] #> <frame 2> (1) #> expr: tryCatchList(expr, classes, parentenv, handlers) #> env: [frame 0x5616e49e0d18] #> #> [[35]] #> <frame 1> (0) #> expr: tryCatch(withCallingHandlers({ <...> #> env: [frame 0x5616e49dd0e0] #> #> [[36]] #> <frame 0> [global] #> expr: NULL #> env: [global] #> #> attr(,"class") #> [1] "ctxt_stack" "stack"#> [[1]] #> <frame 37> (35) #> expr: identity(ctxt_stack()) #> env: [local 0x5616e79b83c0] #> #> [[2]] #> <frame 36> (35) #> expr: identity(identity(ctxt_stack())) #> env: [local 0x5616e79b8238] #> #> [[3]] #> <frame 35> (34) #> expr: eval(expr, envir, enclos) #> env: [local 0x5616eb2f6cc8] #> #> [[4]] #> <frame 34> (24) #> expr: eval(expr, envir, enclos) #> env: [local 0x5616e79b8078] #> #> [[5]] #> <frame 33> (24) #> expr: withVisible(eval(expr, envir, enclos)) #> env: [local 0x5616e79b7cc0] #> #> [[6]] #> <frame 32> (24) #> expr: withCallingHandlers(withVisible(eval(expr, envir, enclos)), warning = wHandler, <...> #> env: [local 0x5616e79bed70] #> #> [[7]] #> <frame 31> (30) #> expr: doTryCatch(return(expr), name, parentenv, handler) #> env: [local 0x5616e79be168] #> #> [[8]] #> <frame 30> (29) #> expr: tryCatchOne(expr, names, parentenv, handlers[[1L]]) #> env: [local 0x5616e79bdc28] #> #> [[9]] #> <frame 29> (28) #> expr: tryCatchList(expr, classes, parentenv, handlers) #> env: [local 0x5616e79bd790] #> #> [[10]] #> <frame 28> (27) #> expr: tryCatch(expr, error = function(e) { <...> #> env: [local 0x5616e79c0a28] #> #> [[11]] #> <frame 27> (26) #> expr: try(f, silent = TRUE) #> env: [local 0x5616e79c06e0] #> #> [[12]] #> <frame 26> (24) #> expr: handle(ev <- withCallingHandlers(withVisible(eval(expr, envir, <...> #> env: [local 0x5616e79c04e8] #> #> [[13]] #> <frame 25> (24) #> expr: timing_fn(handle(ev <- withCallingHandlers(withVisible(eval(expr, <...> #> env: [local 0x5616e79c0328] #> #> [[14]] #> <frame 24> (23) #> expr: evaluate_call(expr, parsed$src[[i]], envir = envir, enclos = enclos, <...> #> env: [frame 0x5616e79e3738] #> #> [[15]] #> <frame 23> (22) #> expr: evaluate::evaluate(code, child_env(env), new_device = TRUE) #> env: [frame 0x5616ee8153d0] #> #> [[16]] #> <frame 22> (21) #> expr: downlit::evaluate_and_highlight(code, fig_save = fig_save_topic, <...> #> env: [frame 0x5616ee80e090] #> #> [[17]] #> <frame 21> (20) #> expr: highlight_examples(code, topic, env = env) #> env: [frame 0x5616ee805670] #> #> [[18]] #> <frame 20> (19) #> expr: run_examples(tags$tag_examples[[1]], env = new.env(parent = globalenv()), <...> #> env: [frame 0x5616ec34dcb8] #> #> [[19]] #> <frame 19> (17) #> expr: data_reference_topic(topic, pkg, examples = examples, run_dont_run = run_dont_run) #> env: [frame 0x5616eb5431c8] #> #> [[20]] #> <frame 18> (17) #> expr: withCallingHandlers(data_reference_topic(topic, pkg, examples = examples, <...> #> env: [frame 0x5616eb543900] #> #> [[21]] #> <frame 17> (16) #> expr: .f(.x[[i]], ...) #> env: [frame 0x5616eaef8a88] #> #> [[22]] #> <frame 16> (15) #> expr: purrr::map(topics, build_reference_topic, pkg = pkg, lazy = lazy, <...> #> env: [frame 0x5616e726b258] #> #> [[23]] #> <frame 15> (14) #> expr: build_reference(pkg, lazy = lazy, examples = examples, run_dont_run = run_dont_run, <...> #> env: [frame 0x5616e6c5d868] #> #> [[24]] #> <frame 14> (13) #> expr: build_site_local(pkg = pkg, examples = examples, run_dont_run = run_dont_run, <...> #> env: [frame 0x5616e4de4458] #> #> [[25]] #> <frame 13> (12) #> expr: pkgdown::build_site(...) #> env: [frame 0x5616e4da9bc0] #> #> [[26]] #> <frame 12> (0) #> expr: (function (..., crayon_enabled, crayon_colors, pkgdown_internet) <...> #> env: [frame 0x5616e426fef0] #> #> [[27]] #> <frame 11> (0) #> expr: (function (what, args, quote = FALSE, envir = parent.frame()) <...> #> env: [frame 0x5616e426ede0] #> #> [[28]] #> <frame 10> (0) #> expr: do.call(do.call, c(readRDS("/tmp/RtmpJYaP2e/callr-fun-7b2c52a64aa5"), <...> #> env: [frame 0x5616e49e25a8] #> #> [[29]] #> <frame 9> (0) #> expr: saveRDS(do.call(do.call, c(readRDS("/tmp/RtmpJYaP2e/callr-fun-7b2c52a64aa5"), <...> #> env: [frame 0x5616e49e2928] #> #> [[30]] #> <frame 8> (0) #> expr: withCallingHandlers({ <...> #> env: [frame 0x5616e49df348] #> #> [[31]] #> <frame 7> (6) #> expr: doTryCatch(return(expr), name, parentenv, handler) #> env: [frame 0x5616e49df9d8] #> #> [[32]] #> <frame 6> (5) #> expr: tryCatchOne(expr, names, parentenv, handlers[[1L]]) #> env: [frame 0x5616e49dfd20] #> #> [[33]] #> <frame 5> (2) #> expr: tryCatchList(expr, names[-nh], parentenv, handlers[-nh]) #> env: [frame 0x5616e49e00d8] #> #> [[34]] #> <frame 4> (3) #> expr: doTryCatch(return(expr), name, parentenv, handler) #> env: [frame 0x5616e49e0688] #> #> [[35]] #> <frame 3> (2) #> expr: tryCatchOne(tryCatchList(expr, names[-nh], parentenv, handlers[-nh]), <...> #> env: [frame 0x5616e49e09d0] #> #> [[36]] #> <frame 2> (1) #> expr: tryCatchList(expr, classes, parentenv, handlers) #> env: [frame 0x5616e49e0d18] #> #> [[37]] #> <frame 1> (0) #> expr: tryCatch(withCallingHandlers({ <...> #> env: [frame 0x5616e49dd0e0] #> #> [[38]] #> <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