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 0x555f4503af68] #> #> [[2]] #> <frame 32> (22) #> expr: eval(expr, envir, enclos) #> env: [local 0x555f4252d5a8] #> #> [[3]] #> <frame 31> (22) #> expr: withVisible(eval(expr, envir, enclos)) #> env: [local 0x555f4252d7d8] #> #> [[4]] #> <frame 30> (22) #> expr: withCallingHandlers(withVisible(eval(expr, envir, enclos)), warning = wHandler, <...> #> env: [local 0x555f4252dd88] #> #> [[5]] #> <frame 29> (28) #> expr: doTryCatch(return(expr), name, parentenv, handler) #> env: [local 0x555f4252e300] #> #> [[6]] #> <frame 28> (27) #> expr: tryCatchOne(expr, names, parentenv, handlers[[1L]]) #> env: [local 0x555f4252e680] #> #> [[7]] #> <frame 27> (26) #> expr: tryCatchList(expr, classes, parentenv, handlers) #> env: [local 0x555f4252e9c8] #> #> [[8]] #> <frame 26> (25) #> expr: tryCatch(expr, error = function(e) { <...> #> env: [local 0x555f3f724258] #> #> [[9]] #> <frame 25> (24) #> expr: try(f, silent = TRUE) #> env: [local 0x555f3f724530] #> #> [[10]] #> <frame 24> (22) #> expr: handle(ev <- withCallingHandlers(withVisible(eval(expr, envir, <...> #> env: [local 0x555f3f7246b8] #> #> [[11]] #> <frame 23> (22) #> expr: timing_fn(handle(ev <- withCallingHandlers(withVisible(eval(expr, <...> #> env: [local 0x555f3f724798] #> #> [[12]] #> <frame 22> (21) #> expr: evaluate_call(expr, parsed$src[[i]], envir = envir, enclos = enclos, <...> #> env: [frame 0x555f40ec1280] #> #> [[13]] #> <frame 21> (20) #> expr: evaluate::evaluate(x, child_env(env), new_device = TRUE) #> env: [frame 0x555f473f56f8] #> #> [[14]] #> <frame 20> (19) #> expr: highlight_examples(code, topic, env = env) #> env: [frame 0x555f473eda78] #> #> [[15]] #> <frame 19> (18) #> expr: run_examples(tags$tag_examples[[1]], env = new.env(parent = globalenv()), <...> #> env: [frame 0x555f47195918] #> #> [[16]] #> <frame 18> (17) #> expr: data_reference_topic(topic, pkg, examples = examples, run_dont_run = run_dont_run) #> env: [frame 0x555f46c07480] #> #> [[17]] #> <frame 17> (16) #> expr: .f(.x[[i]], ...) #> env: [frame 0x555f46ba64e8] #> #> [[18]] #> <frame 16> (15) #> expr: purrr::map(topics, build_reference_topic, pkg = pkg, lazy = lazy, <...> #> env: [frame 0x555f3cc9b7f8] #> #> [[19]] #> <frame 15> (14) #> expr: build_reference(pkg, lazy = lazy, examples = examples, run_dont_run = run_dont_run, <...> #> env: [frame 0x555f3ad79698] #> #> [[20]] #> <frame 14> (13) #> expr: build_site_local(pkg = pkg, examples = examples, run_dont_run = run_dont_run, <...> #> env: [frame 0x555f397076c8] #> #> [[21]] #> <frame 13> (12) #> expr: pkgdown::build_site(...) #> env: [frame 0x555f39c40618] #> #> [[22]] #> <frame 12> (0) #> expr: (function (..., crayon_enabled, crayon_colors, pkgdown_internet) <...> #> env: [frame 0x555f39c95938] #> #> [[23]] #> <frame 11> (0) #> expr: (function (what, args, quote = FALSE, envir = parent.frame()) <...> #> env: [frame 0x555f39c94828] #> #> [[24]] #> <frame 10> (0) #> expr: do.call(do.call, c(readRDS("/tmp/RtmpivJ8hr/callr-fun-1c30651e92ec"), <...> #> env: [frame 0x555f3b324c98] #> #> [[25]] #> <frame 9> (0) #> expr: saveRDS(do.call(do.call, c(readRDS("/tmp/RtmpivJ8hr/callr-fun-1c30651e92ec"), <...> #> env: [frame 0x555f3b325018] #> #> [[26]] #> <frame 8> (0) #> expr: withCallingHandlers({ <...> #> env: [frame 0x555f3b321a38] #> #> [[27]] #> <frame 7> (6) #> expr: doTryCatch(return(expr), name, parentenv, handler) #> env: [frame 0x555f3b3220c8] #> #> [[28]] #> <frame 6> (5) #> expr: tryCatchOne(expr, names, parentenv, handlers[[1L]]) #> env: [frame 0x555f3b322410] #> #> [[29]] #> <frame 5> (2) #> expr: tryCatchList(expr, names[-nh], parentenv, handlers[-nh]) #> env: [frame 0x555f3b3227c8] #> #> [[30]] #> <frame 4> (3) #> expr: doTryCatch(return(expr), name, parentenv, handler) #> env: [frame 0x555f3b322d78] #> #> [[31]] #> <frame 3> (2) #> expr: tryCatchOne(tryCatchList(expr, names[-nh], parentenv, handlers[-nh]), <...> #> env: [frame 0x555f3b3230c0] #> #> [[32]] #> <frame 2> (1) #> expr: tryCatchList(expr, classes, parentenv, handlers) #> env: [frame 0x555f3b323408] #> #> [[33]] #> <frame 1> (0) #> expr: tryCatch(withCallingHandlers({ <...> #> env: [frame 0x555f3b31fd10] #> #> [[34]] #> <frame 0> [global] #> expr: NULL #> env: [global] #> #> attr(,"class") #> [1] "ctxt_stack" "stack"#> [[1]] #> <frame 35> (33) #> expr: identity(ctxt_stack()) #> env: [local 0x555f43843660] #> #> [[2]] #> <frame 34> (33) #> expr: identity(identity(ctxt_stack())) #> env: [local 0x555f43843548] #> #> [[3]] #> <frame 33> (32) #> expr: eval(expr, envir, enclos) #> env: [local 0x555f4503af68] #> #> [[4]] #> <frame 32> (22) #> expr: eval(expr, envir, enclos) #> env: [local 0x555f43843388] #> #> [[5]] #> <frame 31> (22) #> expr: withVisible(eval(expr, envir, enclos)) #> env: [local 0x555f43843158] #> #> [[6]] #> <frame 30> (22) #> expr: withCallingHandlers(withVisible(eval(expr, envir, enclos)), warning = wHandler, <...> #> env: [local 0x555f43842ac8] #> #> [[7]] #> <frame 29> (28) #> expr: doTryCatch(return(expr), name, parentenv, handler) #> env: [local 0x555f43842390] #> #> [[8]] #> <frame 28> (27) #> expr: tryCatchOne(expr, names, parentenv, handlers[[1L]]) #> env: [local 0x555f43841fa0] #> #> [[9]] #> <frame 27> (26) #> expr: tryCatchList(expr, classes, parentenv, handlers) #> env: [local 0x555f4384b468] #> #> [[10]] #> <frame 26> (25) #> expr: tryCatch(expr, error = function(e) { <...> #> env: [local 0x555f4384abe0] #> #> [[11]] #> <frame 25> (24) #> expr: try(f, silent = TRUE) #> env: [local 0x555f4384a908] #> #> [[12]] #> <frame 24> (22) #> expr: handle(ev <- withCallingHandlers(withVisible(eval(expr, envir, <...> #> env: [local 0x555f4384a780] #> #> [[13]] #> <frame 23> (22) #> expr: timing_fn(handle(ev <- withCallingHandlers(withVisible(eval(expr, <...> #> env: [local 0x555f4384a6a0] #> #> [[14]] #> <frame 22> (21) #> expr: evaluate_call(expr, parsed$src[[i]], envir = envir, enclos = enclos, <...> #> env: [frame 0x555f41f8bf10] #> #> [[15]] #> <frame 21> (20) #> expr: evaluate::evaluate(x, child_env(env), new_device = TRUE) #> env: [frame 0x555f473f56f8] #> #> [[16]] #> <frame 20> (19) #> expr: highlight_examples(code, topic, env = env) #> env: [frame 0x555f473eda78] #> #> [[17]] #> <frame 19> (18) #> expr: run_examples(tags$tag_examples[[1]], env = new.env(parent = globalenv()), <...> #> env: [frame 0x555f47195918] #> #> [[18]] #> <frame 18> (17) #> expr: data_reference_topic(topic, pkg, examples = examples, run_dont_run = run_dont_run) #> env: [frame 0x555f46c07480] #> #> [[19]] #> <frame 17> (16) #> expr: .f(.x[[i]], ...) #> env: [frame 0x555f46ba64e8] #> #> [[20]] #> <frame 16> (15) #> expr: purrr::map(topics, build_reference_topic, pkg = pkg, lazy = lazy, <...> #> env: [frame 0x555f3cc9b7f8] #> #> [[21]] #> <frame 15> (14) #> expr: build_reference(pkg, lazy = lazy, examples = examples, run_dont_run = run_dont_run, <...> #> env: [frame 0x555f3ad79698] #> #> [[22]] #> <frame 14> (13) #> expr: build_site_local(pkg = pkg, examples = examples, run_dont_run = run_dont_run, <...> #> env: [frame 0x555f397076c8] #> #> [[23]] #> <frame 13> (12) #> expr: pkgdown::build_site(...) #> env: [frame 0x555f39c40618] #> #> [[24]] #> <frame 12> (0) #> expr: (function (..., crayon_enabled, crayon_colors, pkgdown_internet) <...> #> env: [frame 0x555f39c95938] #> #> [[25]] #> <frame 11> (0) #> expr: (function (what, args, quote = FALSE, envir = parent.frame()) <...> #> env: [frame 0x555f39c94828] #> #> [[26]] #> <frame 10> (0) #> expr: do.call(do.call, c(readRDS("/tmp/RtmpivJ8hr/callr-fun-1c30651e92ec"), <...> #> env: [frame 0x555f3b324c98] #> #> [[27]] #> <frame 9> (0) #> expr: saveRDS(do.call(do.call, c(readRDS("/tmp/RtmpivJ8hr/callr-fun-1c30651e92ec"), <...> #> env: [frame 0x555f3b325018] #> #> [[28]] #> <frame 8> (0) #> expr: withCallingHandlers({ <...> #> env: [frame 0x555f3b321a38] #> #> [[29]] #> <frame 7> (6) #> expr: doTryCatch(return(expr), name, parentenv, handler) #> env: [frame 0x555f3b3220c8] #> #> [[30]] #> <frame 6> (5) #> expr: tryCatchOne(expr, names, parentenv, handlers[[1L]]) #> env: [frame 0x555f3b322410] #> #> [[31]] #> <frame 5> (2) #> expr: tryCatchList(expr, names[-nh], parentenv, handlers[-nh]) #> env: [frame 0x555f3b3227c8] #> #> [[32]] #> <frame 4> (3) #> expr: doTryCatch(return(expr), name, parentenv, handler) #> env: [frame 0x555f3b322d78] #> #> [[33]] #> <frame 3> (2) #> expr: tryCatchOne(tryCatchList(expr, names[-nh], parentenv, handlers[-nh]), <...> #> env: [frame 0x555f3b3230c0] #> #> [[34]] #> <frame 2> (1) #> expr: tryCatchList(expr, classes, parentenv, handlers) #> env: [frame 0x555f3b323408] #> #> [[35]] #> <frame 1> (0) #> expr: tryCatch(withCallingHandlers({ <...> #> env: [frame 0x555f3b31fd10] #> #> [[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