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 0x563611fdd7b8] #> #> [[2]] #> <frame 32> (22) #> expr: eval(expr, envir, enclos) #> env: [local 0x56360e135280] #> #> [[3]] #> <frame 31> (22) #> expr: withVisible(eval(expr, envir, enclos)) #> env: [local 0x56360e135050] #> #> [[4]] #> <frame 30> (22) #> expr: withCallingHandlers(withVisible(eval(expr, envir, enclos)), warning = wHandler, <...> #> env: [local 0x56360e134a68] #> #> [[5]] #> <frame 29> (28) #> expr: doTryCatch(return(expr), name, parentenv, handler) #> env: [local 0x56360e134480] #> #> [[6]] #> <frame 28> (27) #> expr: tryCatchOne(expr, names, parentenv, handlers[[1L]]) #> env: [local 0x56360e1340c8] #> #> [[7]] #> <frame 27> (26) #> expr: tryCatchList(expr, classes, parentenv, handlers) #> env: [local 0x56360e133d10] #> #> [[8]] #> <frame 26> (25) #> expr: tryCatch(expr, error = function(e) { <...> #> env: [local 0x56360e133530] #> #> [[9]] #> <frame 25> (24) #> expr: try(f, silent = TRUE) #> env: [local 0x56360e1370c0] #> #> [[10]] #> <frame 24> (22) #> expr: handle(ev <- withCallingHandlers(withVisible(eval(expr, envir, <...> #> env: [local 0x56360e136f38] #> #> [[11]] #> <frame 23> (22) #> expr: timing_fn(handle(ev <- withCallingHandlers(withVisible(eval(expr, <...> #> env: [local 0x56360e136e58] #> #> [[12]] #> <frame 22> (21) #> expr: evaluate_call(expr, parsed$src[[i]], envir = envir, enclos = enclos, <...> #> env: [frame 0x56360e1d2010] #> #> [[13]] #> <frame 21> (20) #> expr: evaluate::evaluate(x, child_env(env), new_device = TRUE) #> env: [frame 0x56361358acd0] #> #> [[14]] #> <frame 20> (19) #> expr: highlight_examples(code, topic, env = env) #> env: [frame 0x5636135830f8] #> #> [[15]] #> <frame 19> (18) #> expr: run_examples(tags$tag_examples[[1]], env = new.env(parent = globalenv()), <...> #> env: [frame 0x563611b180a0] #> #> [[16]] #> <frame 18> (17) #> expr: data_reference_topic(topic, pkg, examples = examples, run_dont_run = run_dont_run) #> env: [frame 0x563617f4aa78] #> #> [[17]] #> <frame 17> (16) #> expr: .f(.x[[i]], ...) #> env: [frame 0x563617ecd0f8] #> #> [[18]] #> <frame 16> (15) #> expr: purrr::map(topics, build_reference_topic, pkg = pkg, lazy = lazy, <...> #> env: [frame 0x56360d12b998] #> #> [[19]] #> <frame 15> (14) #> expr: build_reference(pkg, lazy = lazy, examples = examples, run_dont_run = run_dont_run, <...> #> env: [frame 0x56360cdece38] #> #> [[20]] #> <frame 14> (13) #> expr: build_site_local(pkg = pkg, examples = examples, run_dont_run = run_dont_run, <...> #> env: [frame 0x5636092ab548] #> #> [[21]] #> <frame 13> (12) #> expr: pkgdown::build_site(...) #> env: [frame 0x563609d1c300] #> #> [[22]] #> <frame 12> (0) #> expr: (function (..., crayon_enabled, crayon_colors, pkgdown_internet) <...> #> env: [frame 0x563609d56a80] #> #> [[23]] #> <frame 11> (0) #> expr: (function (what, args, quote = FALSE, envir = parent.frame()) <...> #> env: [frame 0x563609d5b810] #> #> [[24]] #> <frame 10> (0) #> expr: do.call(do.call, c(readRDS("/tmp/RtmpKEt7mB/callr-fun-1b89556ad30a"), <...> #> env: [frame 0x56360b4654e0] #> #> [[25]] #> <frame 9> (0) #> expr: saveRDS(do.call(do.call, c(readRDS("/tmp/RtmpKEt7mB/callr-fun-1b89556ad30a"), <...> #> env: [frame 0x56360b465860] #> #> [[26]] #> <frame 8> (0) #> expr: withCallingHandlers({ <...> #> env: [frame 0x56360b4660b0] #> #> [[27]] #> <frame 7> (6) #> expr: doTryCatch(return(expr), name, parentenv, handler) #> env: [frame 0x56360b466740] #> #> [[28]] #> <frame 6> (5) #> expr: tryCatchOne(expr, names, parentenv, handlers[[1L]]) #> env: [frame 0x56360b460d38] #> #> [[29]] #> <frame 5> (2) #> expr: tryCatchList(expr, names[-nh], parentenv, handlers[-nh]) #> env: [frame 0x56360b4610f0] #> #> [[30]] #> <frame 4> (3) #> expr: doTryCatch(return(expr), name, parentenv, handler) #> env: [frame 0x56360b4616a0] #> #> [[31]] #> <frame 3> (2) #> expr: tryCatchOne(tryCatchList(expr, names[-nh], parentenv, handlers[-nh]), <...> #> env: [frame 0x56360b4619e8] #> #> [[32]] #> <frame 2> (1) #> expr: tryCatchList(expr, classes, parentenv, handlers) #> env: [frame 0x56360b461d30] #> #> [[33]] #> <frame 1> (0) #> expr: tryCatch(withCallingHandlers({ <...> #> env: [frame 0x56360b462468] #> #> [[34]] #> <frame 0> [global] #> expr: NULL #> env: [global] #> #> attr(,"class") #> [1] "ctxt_stack" "stack"#> [[1]] #> <frame 35> (33) #> expr: identity(ctxt_stack()) #> env: [local 0x56360d44a328] #> #> [[2]] #> <frame 34> (33) #> expr: identity(identity(ctxt_stack())) #> env: [local 0x56360d44e040] #> #> [[3]] #> <frame 33> (32) #> expr: eval(expr, envir, enclos) #> env: [local 0x563611fdd7b8] #> #> [[4]] #> <frame 32> (22) #> expr: eval(expr, envir, enclos) #> env: [local 0x56360d44dda0] #> #> [[5]] #> <frame 31> (22) #> expr: withVisible(eval(expr, envir, enclos)) #> env: [local 0x56360d44dac8] #> #> [[6]] #> <frame 30> (22) #> expr: withCallingHandlers(withVisible(eval(expr, envir, enclos)), warning = wHandler, <...> #> env: [local 0x56360d44d2e8] #> #> [[7]] #> <frame 29> (28) #> expr: doTryCatch(return(expr), name, parentenv, handler) #> env: [local 0x56360d44cc20] #> #> [[8]] #> <frame 28> (27) #> expr: tryCatchOne(expr, names, parentenv, handlers[[1L]]) #> env: [local 0x56360d44fcc0] #> #> [[9]] #> <frame 27> (26) #> expr: tryCatchList(expr, classes, parentenv, handlers) #> env: [local 0x56360d44f828] #> #> [[10]] #> <frame 26> (25) #> expr: tryCatch(expr, error = function(e) { <...> #> env: [local 0x56360d44f010] #> #> [[11]] #> <frame 25> (24) #> expr: try(f, silent = TRUE) #> env: [local 0x56360d44e750] #> #> [[12]] #> <frame 24> (22) #> expr: handle(ev <- withCallingHandlers(withVisible(eval(expr, envir, <...> #> env: [local 0x56360d44e5c8] #> #> [[13]] #> <frame 23> (22) #> expr: timing_fn(handle(ev <- withCallingHandlers(withVisible(eval(expr, <...> #> env: [local 0x56360d44e478] #> #> [[14]] #> <frame 22> (21) #> expr: evaluate_call(expr, parsed$src[[i]], envir = envir, enclos = enclos, <...> #> env: [frame 0x56360d499850] #> #> [[15]] #> <frame 21> (20) #> expr: evaluate::evaluate(x, child_env(env), new_device = TRUE) #> env: [frame 0x56361358acd0] #> #> [[16]] #> <frame 20> (19) #> expr: highlight_examples(code, topic, env = env) #> env: [frame 0x5636135830f8] #> #> [[17]] #> <frame 19> (18) #> expr: run_examples(tags$tag_examples[[1]], env = new.env(parent = globalenv()), <...> #> env: [frame 0x563611b180a0] #> #> [[18]] #> <frame 18> (17) #> expr: data_reference_topic(topic, pkg, examples = examples, run_dont_run = run_dont_run) #> env: [frame 0x563617f4aa78] #> #> [[19]] #> <frame 17> (16) #> expr: .f(.x[[i]], ...) #> env: [frame 0x563617ecd0f8] #> #> [[20]] #> <frame 16> (15) #> expr: purrr::map(topics, build_reference_topic, pkg = pkg, lazy = lazy, <...> #> env: [frame 0x56360d12b998] #> #> [[21]] #> <frame 15> (14) #> expr: build_reference(pkg, lazy = lazy, examples = examples, run_dont_run = run_dont_run, <...> #> env: [frame 0x56360cdece38] #> #> [[22]] #> <frame 14> (13) #> expr: build_site_local(pkg = pkg, examples = examples, run_dont_run = run_dont_run, <...> #> env: [frame 0x5636092ab548] #> #> [[23]] #> <frame 13> (12) #> expr: pkgdown::build_site(...) #> env: [frame 0x563609d1c300] #> #> [[24]] #> <frame 12> (0) #> expr: (function (..., crayon_enabled, crayon_colors, pkgdown_internet) <...> #> env: [frame 0x563609d56a80] #> #> [[25]] #> <frame 11> (0) #> expr: (function (what, args, quote = FALSE, envir = parent.frame()) <...> #> env: [frame 0x563609d5b810] #> #> [[26]] #> <frame 10> (0) #> expr: do.call(do.call, c(readRDS("/tmp/RtmpKEt7mB/callr-fun-1b89556ad30a"), <...> #> env: [frame 0x56360b4654e0] #> #> [[27]] #> <frame 9> (0) #> expr: saveRDS(do.call(do.call, c(readRDS("/tmp/RtmpKEt7mB/callr-fun-1b89556ad30a"), <...> #> env: [frame 0x56360b465860] #> #> [[28]] #> <frame 8> (0) #> expr: withCallingHandlers({ <...> #> env: [frame 0x56360b4660b0] #> #> [[29]] #> <frame 7> (6) #> expr: doTryCatch(return(expr), name, parentenv, handler) #> env: [frame 0x56360b466740] #> #> [[30]] #> <frame 6> (5) #> expr: tryCatchOne(expr, names, parentenv, handlers[[1L]]) #> env: [frame 0x56360b460d38] #> #> [[31]] #> <frame 5> (2) #> expr: tryCatchList(expr, names[-nh], parentenv, handlers[-nh]) #> env: [frame 0x56360b4610f0] #> #> [[32]] #> <frame 4> (3) #> expr: doTryCatch(return(expr), name, parentenv, handler) #> env: [frame 0x56360b4616a0] #> #> [[33]] #> <frame 3> (2) #> expr: tryCatchOne(tryCatchList(expr, names[-nh], parentenv, handlers[-nh]), <...> #> env: [frame 0x56360b4619e8] #> #> [[34]] #> <frame 2> (1) #> expr: tryCatchList(expr, classes, parentenv, handlers) #> env: [frame 0x56360b461d30] #> #> [[35]] #> <frame 1> (0) #> expr: tryCatch(withCallingHandlers({ <...> #> env: [frame 0x56360b462468] #> #> [[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