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 0x555823a1c8c8] #> #> [[2]] #> <frame 34> (24) #> expr: eval(expr, envir, enclos) #> env: [local 0x555822de34d0] #> #> [[3]] #> <frame 33> (24) #> expr: withVisible(eval(expr, envir, enclos)) #> env: [local 0x555822de7028] #> #> [[4]] #> <frame 32> (24) #> expr: withCallingHandlers(withVisible(eval(expr, envir, enclos)), warning = wHandler, <...> #> env: [local 0x555822de6928] #> #> [[5]] #> <frame 31> (30) #> expr: doTryCatch(return(expr), name, parentenv, handler) #> env: [local 0x555822de60d8] #> #> [[6]] #> <frame 30> (29) #> expr: tryCatchOne(expr, names, parentenv, handlers[[1L]]) #> env: [local 0x555822de5c78] #> #> [[7]] #> <frame 29> (28) #> expr: tryCatchList(expr, classes, parentenv, handlers) #> env: [local 0x555822de8fb8] #> #> [[8]] #> <frame 28> (27) #> expr: tryCatch(expr, error = function(e) { <...> #> env: [local 0x555822de87d8] #> #> [[9]] #> <frame 27> (26) #> expr: try(f, silent = TRUE) #> env: [local 0x555822de8500] #> #> [[10]] #> <frame 26> (24) #> expr: handle(ev <- withCallingHandlers(withVisible(eval(expr, envir, <...> #> env: [local 0x555822de8378] #> #> [[11]] #> <frame 25> (24) #> expr: timing_fn(handle(ev <- withCallingHandlers(withVisible(eval(expr, <...> #> env: [local 0x555822de8228] #> #> [[12]] #> <frame 24> (23) #> expr: evaluate_call(expr, parsed$src[[i]], envir = envir, enclos = enclos, <...> #> env: [frame 0x555822e12498] #> #> [[13]] #> <frame 23> (22) #> expr: evaluate::evaluate(code, child_env(env), new_device = TRUE) #> env: [frame 0x555824187b78] #> #> [[14]] #> <frame 22> (21) #> expr: downlit::evaluate_and_highlight(code, fig_save = fig_save_topic, <...> #> env: [frame 0x55582418bb78] #> #> [[15]] #> <frame 21> (20) #> expr: highlight_examples(code, topic, env = env) #> env: [frame 0x55582419bdc8] #> #> [[16]] #> <frame 20> (19) #> expr: run_examples(tags$tag_examples[[1]], env = new.env(parent = globalenv()), <...> #> env: [frame 0x55582421a050] #> #> [[17]] #> <frame 19> (17) #> expr: data_reference_topic(topic, pkg, examples = examples, run_dont_run = run_dont_run) #> env: [frame 0x555822294e10] #> #> [[18]] #> <frame 18> (17) #> expr: withCallingHandlers(data_reference_topic(topic, pkg, examples = examples, <...> #> env: [frame 0x555822b71840] #> #> [[19]] #> <frame 17> (16) #> expr: .f(.x[[i]], ...) #> env: [frame 0x5558207c8a70] #> #> [[20]] #> <frame 16> (15) #> expr: purrr::map(topics, build_reference_topic, pkg = pkg, lazy = lazy, <...> #> env: [frame 0x555823d9bdb8] #> #> [[21]] #> <frame 15> (14) #> expr: build_reference(pkg, lazy = lazy, examples = examples, run_dont_run = run_dont_run, <...> #> env: [frame 0x5558237b07b8] #> #> [[22]] #> <frame 14> (13) #> expr: build_site_local(pkg = pkg, examples = examples, run_dont_run = run_dont_run, <...> #> env: [frame 0x5558202388f8] #> #> [[23]] #> <frame 13> (12) #> expr: pkgdown::build_site(...) #> env: [frame 0x55582108b050] #> #> [[24]] #> <frame 12> (0) #> expr: (function (..., crayon_enabled, crayon_colors, pkgdown_internet) <...> #> env: [frame 0x55582028b4a0] #> #> [[25]] #> <frame 11> (0) #> expr: (function (what, args, quote = FALSE, envir = parent.frame()) <...> #> env: [frame 0x55582029fbb0] #> #> [[26]] #> <frame 10> (0) #> expr: do.call(do.call, c(readRDS("/tmp/Rtmp1mG078/callr-fun-1f7d76d7f70d"), <...> #> env: [frame 0x555820e984d0] #> #> [[27]] #> <frame 9> (0) #> expr: saveRDS(do.call(do.call, c(readRDS("/tmp/Rtmp1mG078/callr-fun-1f7d76d7f70d"), <...> #> env: [frame 0x555820e988c0] #> #> [[28]] #> <frame 8> (0) #> expr: withCallingHandlers({ <...> #> env: [frame 0x555820e99110] #> #> [[29]] #> <frame 7> (6) #> expr: doTryCatch(return(expr), name, parentenv, handler) #> env: [frame 0x555820e997a0] #> #> [[30]] #> <frame 6> (5) #> expr: tryCatchOne(expr, names, parentenv, handlers[[1L]]) #> env: [frame 0x555820e99ae8] #> #> [[31]] #> <frame 5> (2) #> expr: tryCatchList(expr, names[-nh], parentenv, handlers[-nh]) #> env: [frame 0x555820e99ea0] #> #> [[32]] #> <frame 4> (3) #> expr: doTryCatch(return(expr), name, parentenv, handler) #> env: [frame 0x555820e91b40] #> #> [[33]] #> <frame 3> (2) #> expr: tryCatchOne(tryCatchList(expr, names[-nh], parentenv, handlers[-nh]), <...> #> env: [frame 0x555820e91e88] #> #> [[34]] #> <frame 2> (1) #> expr: tryCatchList(expr, classes, parentenv, handlers) #> env: [frame 0x555820e921d0] #> #> [[35]] #> <frame 1> (0) #> expr: tryCatch(withCallingHandlers({ <...> #> env: [frame 0x555820e8d918] #> #> [[36]] #> <frame 0> [global] #> expr: NULL #> env: [global] #> #> attr(,"class") #> [1] "ctxt_stack" "stack"#> [[1]] #> <frame 37> (35) #> expr: identity(ctxt_stack()) #> env: [local 0x555822796680] #> #> [[2]] #> <frame 36> (35) #> expr: identity(identity(ctxt_stack())) #> env: [local 0x555822796488] #> #> [[3]] #> <frame 35> (34) #> expr: eval(expr, envir, enclos) #> env: [local 0x555823a1c8c8] #> #> [[4]] #> <frame 34> (24) #> expr: eval(expr, envir, enclos) #> env: [local 0x555822796258] #> #> [[5]] #> <frame 33> (24) #> expr: withVisible(eval(expr, envir, enclos)) #> env: [local 0x555822796028] #> #> [[6]] #> <frame 32> (24) #> expr: withCallingHandlers(withVisible(eval(expr, envir, enclos)), warning = wHandler, <...> #> env: [local 0x5558227958b8] #> #> [[7]] #> <frame 31> (30) #> expr: doTryCatch(return(expr), name, parentenv, handler) #> env: [local 0x555822798aa8] #> #> [[8]] #> <frame 30> (29) #> expr: tryCatchOne(expr, names, parentenv, handlers[[1L]]) #> env: [local 0x555822798680] #> #> [[9]] #> <frame 29> (28) #> expr: tryCatchList(expr, classes, parentenv, handlers) #> env: [local 0x555822798258] #> #> [[10]] #> <frame 28> (27) #> expr: tryCatch(expr, error = function(e) { <...> #> env: [local 0x555822797848] #> #> [[11]] #> <frame 27> (26) #> expr: try(f, silent = TRUE) #> env: [local 0x555822797570] #> #> [[12]] #> <frame 26> (24) #> expr: handle(ev <- withCallingHandlers(withVisible(eval(expr, envir, <...> #> env: [local 0x555822797378] #> #> [[13]] #> <frame 25> (24) #> expr: timing_fn(handle(ev <- withCallingHandlers(withVisible(eval(expr, <...> #> env: [local 0x555822797110] #> #> [[14]] #> <frame 24> (23) #> expr: evaluate_call(expr, parsed$src[[i]], envir = envir, enclos = enclos, <...> #> env: [frame 0x5558227bb180] #> #> [[15]] #> <frame 23> (22) #> expr: evaluate::evaluate(code, child_env(env), new_device = TRUE) #> env: [frame 0x555824187b78] #> #> [[16]] #> <frame 22> (21) #> expr: downlit::evaluate_and_highlight(code, fig_save = fig_save_topic, <...> #> env: [frame 0x55582418bb78] #> #> [[17]] #> <frame 21> (20) #> expr: highlight_examples(code, topic, env = env) #> env: [frame 0x55582419bdc8] #> #> [[18]] #> <frame 20> (19) #> expr: run_examples(tags$tag_examples[[1]], env = new.env(parent = globalenv()), <...> #> env: [frame 0x55582421a050] #> #> [[19]] #> <frame 19> (17) #> expr: data_reference_topic(topic, pkg, examples = examples, run_dont_run = run_dont_run) #> env: [frame 0x555822294e10] #> #> [[20]] #> <frame 18> (17) #> expr: withCallingHandlers(data_reference_topic(topic, pkg, examples = examples, <...> #> env: [frame 0x555822b71840] #> #> [[21]] #> <frame 17> (16) #> expr: .f(.x[[i]], ...) #> env: [frame 0x5558207c8a70] #> #> [[22]] #> <frame 16> (15) #> expr: purrr::map(topics, build_reference_topic, pkg = pkg, lazy = lazy, <...> #> env: [frame 0x555823d9bdb8] #> #> [[23]] #> <frame 15> (14) #> expr: build_reference(pkg, lazy = lazy, examples = examples, run_dont_run = run_dont_run, <...> #> env: [frame 0x5558237b07b8] #> #> [[24]] #> <frame 14> (13) #> expr: build_site_local(pkg = pkg, examples = examples, run_dont_run = run_dont_run, <...> #> env: [frame 0x5558202388f8] #> #> [[25]] #> <frame 13> (12) #> expr: pkgdown::build_site(...) #> env: [frame 0x55582108b050] #> #> [[26]] #> <frame 12> (0) #> expr: (function (..., crayon_enabled, crayon_colors, pkgdown_internet) <...> #> env: [frame 0x55582028b4a0] #> #> [[27]] #> <frame 11> (0) #> expr: (function (what, args, quote = FALSE, envir = parent.frame()) <...> #> env: [frame 0x55582029fbb0] #> #> [[28]] #> <frame 10> (0) #> expr: do.call(do.call, c(readRDS("/tmp/Rtmp1mG078/callr-fun-1f7d76d7f70d"), <...> #> env: [frame 0x555820e984d0] #> #> [[29]] #> <frame 9> (0) #> expr: saveRDS(do.call(do.call, c(readRDS("/tmp/Rtmp1mG078/callr-fun-1f7d76d7f70d"), <...> #> env: [frame 0x555820e988c0] #> #> [[30]] #> <frame 8> (0) #> expr: withCallingHandlers({ <...> #> env: [frame 0x555820e99110] #> #> [[31]] #> <frame 7> (6) #> expr: doTryCatch(return(expr), name, parentenv, handler) #> env: [frame 0x555820e997a0] #> #> [[32]] #> <frame 6> (5) #> expr: tryCatchOne(expr, names, parentenv, handlers[[1L]]) #> env: [frame 0x555820e99ae8] #> #> [[33]] #> <frame 5> (2) #> expr: tryCatchList(expr, names[-nh], parentenv, handlers[-nh]) #> env: [frame 0x555820e99ea0] #> #> [[34]] #> <frame 4> (3) #> expr: doTryCatch(return(expr), name, parentenv, handler) #> env: [frame 0x555820e91b40] #> #> [[35]] #> <frame 3> (2) #> expr: tryCatchOne(tryCatchList(expr, names[-nh], parentenv, handlers[-nh]), <...> #> env: [frame 0x555820e91e88] #> #> [[36]] #> <frame 2> (1) #> expr: tryCatchList(expr, classes, parentenv, handlers) #> env: [frame 0x555820e921d0] #> #> [[37]] #> <frame 1> (0) #> expr: tryCatch(withCallingHandlers({ <...> #> env: [frame 0x555820e8d918] #> #> [[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