Title: | Low-Cost Anonymous Functions |
---|---|
Description: | Provides a compact variation of the usual syntax of function declaration, in order to support tidyverse-style quasiquotation of a function's arguments and body. |
Authors: | Eugene Ha [aut, cre] |
Maintainer: | Eugene Ha <[email protected]> |
License: | MIT + file LICENSE |
Version: | 0.3.2 |
Built: | 2024-11-03 02:48:40 UTC |
Source: | https://github.com/egnha/nofrills |
as_fn()
is for functions that take functional arguments. Use as_fn()
inside a function to enable it to comprehend a minimal anonymous-function
notation for arguments that are functions. This notation is that of fn()
,
but with ‘fn
’ replaced by ‘.
’ (dot).
as_fn(.f)
as_fn(.f)
.f |
A function or an abbreviated anonymous-function expression of the
form |
as_fn()
cannot follow promise expressions across function calls.
It is only intended to work in the immediate context in which a function
declaration is to be interpreted (see Examples).
If .f
is a function, it is simply returned, otherwise the function
determined by the function declaration is returned.
call_fn <- function(.f, x) { f <- as_fn(.f) f(x) } call_fn(log, 1) call_fn(.(. ~ sin(.) ^ 2), 1) # simplified function expressions support quasiquotation f <- sin call_fn(.(. ~ (!!f)(.) ^ 2), 1) ## wrap Map() to accept abbreviated anonymous function expressions Map_ <- function (f, ...) { f <- as_fn(f) mapply(FUN = f, ..., SIMPLIFY = FALSE) } # you can call Map_() just like Map() Map_(function(x, y, z) paste(x, y, paste("and", z), sep = ", "), 1:3, 4:6, 7:9) # or use a simplified function expression Map_(.(x, y, z ~ paste(x, y, paste("and", z), sep = ", ")), 1:3, 4:6, 7:9) ## abbreviated anonymous functions are interpreted in the calling environment # so this works, as expected foo <- function(a) as_fn(a) foo(.(x ~ x + 1)) # but as_fn() can't interpret abbreviated anonymous functions across calls foo <- function(a) bar(a) bar <- function(b) as_fn(b) ## Not run: foo(.(x ~ x + 1)) ## End(Not run)
call_fn <- function(.f, x) { f <- as_fn(.f) f(x) } call_fn(log, 1) call_fn(.(. ~ sin(.) ^ 2), 1) # simplified function expressions support quasiquotation f <- sin call_fn(.(. ~ (!!f)(.) ^ 2), 1) ## wrap Map() to accept abbreviated anonymous function expressions Map_ <- function (f, ...) { f <- as_fn(f) mapply(FUN = f, ..., SIMPLIFY = FALSE) } # you can call Map_() just like Map() Map_(function(x, y, z) paste(x, y, paste("and", z), sep = ", "), 1:3, 4:6, 7:9) # or use a simplified function expression Map_(.(x, y, z ~ paste(x, y, paste("and", z), sep = ", ")), 1:3, 4:6, 7:9) ## abbreviated anonymous functions are interpreted in the calling environment # so this works, as expected foo <- function(a) as_fn(a) foo(.(x ~ x + 1)) # but as_fn() can't interpret abbreviated anonymous functions across calls foo <- function(a) bar(a) bar <- function(b) as_fn(b) ## Not run: foo(.(x ~ x + 1)) ## End(Not run)
curry()
curries functions—it
reconstitutes a function as a succession of single-argument functions. For
example, curry()
produces the the function
function(x) { function(y) { function(z) { x * y * z } } }
from the function function(x, y, z) x * y * z
.
curry_fn()
produces a curried function from an fn()
-style function
declaration, which supports quasiquotation of a
function’s body and (default) argument values.
curry(f, env = environment(f)) curry_fn(..., ..env = parent.frame())
curry(f, env = environment(f)) curry_fn(..., ..env = parent.frame())
f |
Function. |
env |
Environment of the curried function or |
... |
Function declaration, which supports quasiquotation. |
..env |
Environment in which to create the function (i.e., the function’s enclosing environment). |
Dots (...
) are treated as a unit when currying. For example,
curry()
transforms function(x, ...) list(x, ...)
to
function(x) { function(...) list(x, ...) }
.
A function of nested single-argument functions.
curry(function(x, y, z = 0) x + y + z) double <- curry(`*`)(2) double(3) # 6 curry_fn(x, y, z = 0 ~ x + y + z) curry_fn(target, ... ~ identical(target, ...)) ## Delay unquoting to embed argument values into the innermost function compare_to <- curry_fn(target, x ~ identical(x, QUQ(target))) is_this <- compare_to("this") is_this("that") # FALSE is_this("this") # TRUE classify_as <- curry_fn(class, x ~ `class<-`(x, QUQ(class))) as_this <- classify_as("this") as_this("Some object") # String of class "this"
curry(function(x, y, z = 0) x + y + z) double <- curry(`*`)(2) double(3) # 6 curry_fn(x, y, z = 0 ~ x + y + z) curry_fn(target, ... ~ identical(target, ...)) ## Delay unquoting to embed argument values into the innermost function compare_to <- curry_fn(target, x ~ identical(x, QUQ(target))) is_this <- compare_to("this") is_this("that") # FALSE is_this("this") # TRUE classify_as <- curry_fn(class, x ~ `class<-`(x, QUQ(class))) as_this <- classify_as("this") as_this("Some object") # String of class "this"
fn()
enables you to create (anonymous) functions, of arbitrary call
signature. Use it in place of the usual function()
invocation whenever you
want to:
type less:
fn(x, y = 1 ~ x + y) function(x, y = 1) x + y
are equivalent
guard against changes in lexical scope: by enabling tidyverse
quasiquotation, fn()
allows you to
“burn in” values at the point of function creation (see
Pure functions via quasiquotation)
fn(..., ..env = parent.frame())
fn(..., ..env = parent.frame())
... |
Function declaration, which supports quasiquotation. |
..env |
Environment in which to create the function (i.e., the function’s enclosing environment). |
A function whose enclosing environment is ..env
.
A function declaration is an expression that specifies a function’s arguments and body, as a comma-separated expression of the form
arg1, arg2, ..., argN ~ body
or
arg1, arg2, ..., argN, ~ body
(Note in the second form that the body is a one-sided formula. This distinction is relevant for argument splicing, see below.)
To the left of ~
, you write a conventional function-argument
declaration, just as in function(<arguments>)
: each of arg1
, arg2
,
..., argN
is either a bare argument (e.g., x
or ...
) or an
argument with default value (e.g., x = 1
).
To the right of ~
, you write the function body,
i.e., an expression of the arguments.
All parts of a function declaration support tidyverse quasiquotation:
To unquote values (of arguments or parts of the body), use !!
:
z <- 0 fn(x, y = !!z ~ x + y) fn(x ~ x > !!z)
To unquote argument names (with default value), use :=
(definition operator):
arg <- "y" fn(x, !!arg := 0 ~ x + !!as.name(arg))
To splice in a (formal) list of arguments, use !!!
:
fn(!!!alist(x, y = 0), ~ x + y)
(Note that the body, in this case, must be given as a one-sided formula.)
To write literal unquoting operators, use QUQ()
, QUQS()
:
library(dplyr) my_summarise <- fn(df, ... ~ { group_by <- quos(...) df %>% group_by(QUQS(group_by)) %>% summarise(a = mean(a)) })
(Source: Programming with dplyr)
Functions in R are generally impure, i.e., the return value of a function will not in general be determined by the value of its inputs alone. This is because a function may depend on mutable objects in its lexical scope. Normally this isn’t an issue. But if you are working interactively and sourcing files into the global environment, say, or using a notebook interface (like Jupyter or R Notebook), it can be tricky to ensure that you haven’t unwittingly mutated an object that an earlier function depends upon.
Example — Consider the following function:
a <- 1 foo <- function(x) x + a
What is the value of foo(1)
? It is not necessarily 2
, because the value
of a
may have changed between the creation of foo()
and the calling
of foo(1)
:
foo(1) #> [1] 2 a <- 0 foo(1) #> [1] 1
In other words, foo()
is impure because the value of foo(x)
depends not
only on the value of x
but also on the externally mutable value of a
.
fn()
enables you to write pure functions by using quasiquotation to
eliminate such indeterminacy.
Example — With fn()
, you can unquote a
to “burn in” its
value at the point of creation:
a <- 1 foo <- fn(x ~ x + !!a)
Now foo()
is a pure function, unaffected by changes in its lexical scope:
foo(1) #> [1] 2 a <- 0 foo(1) #> [1] 2
as_fn()
, make_fn_aware()
, curry_fn()
fn(x ~ x + 1) fn(x, y ~ x + y) fn(x, y = 2 ~ x + y) fn(x, y = 1, ... ~ log(x + y, ...)) ## to specify '...' in the middle, write '... = ' fn(x, ... = , y ~ log(x + y, ...)) ## use one-sided formula for constant functions or commands fn(~ NA) fn(~ message("!")) ## unquoting is supported (using `!!` from rlang) zero <- 0 fn(x = !!zero ~ x > !!zero) ## formals and function bodies can also be spliced in f <- function(x, y) x + y g <- function(y, x, ...) x - y frankenstein <- fn(!!!formals(f), ~ !!body(g)) stopifnot(identical(frankenstein, function(x, y) x - y)) ## mixing unquoting and literal unquoting is possible if (suppressWarnings(require(dplyr))) { summariser <- quote(mean) my_summarise <- fn(df, ... ~ { group_by <- quos(...) df %>% group_by(QUQS(group_by)) %>% summarise(a = `!!`(summariser)(a)) }) my_summarise }
fn(x ~ x + 1) fn(x, y ~ x + y) fn(x, y = 2 ~ x + y) fn(x, y = 1, ... ~ log(x + y, ...)) ## to specify '...' in the middle, write '... = ' fn(x, ... = , y ~ log(x + y, ...)) ## use one-sided formula for constant functions or commands fn(~ NA) fn(~ message("!")) ## unquoting is supported (using `!!` from rlang) zero <- 0 fn(x = !!zero ~ x > !!zero) ## formals and function bodies can also be spliced in f <- function(x, y) x + y g <- function(y, x, ...) x - y frankenstein <- fn(!!!formals(f), ~ !!body(g)) stopifnot(identical(frankenstein, function(x, y) x - y)) ## mixing unquoting and literal unquoting is possible if (suppressWarnings(require(dplyr))) { summariser <- quote(mean) my_summarise <- fn(df, ... ~ { group_by <- quos(...) df %>% group_by(QUQS(group_by)) %>% summarise(a = `!!`(summariser)(a)) }) my_summarise }
make_fn_aware()
is a functional operator that enhances a function by
enabling it to interpret abbreviated functional arguments.
make_fn_aware(f, ...)
make_fn_aware(f, ...)
f |
Function, or symbol or name of a function. |
... |
Name(s) of functional argument(s) of |
A function with the same call signature as f
, but whose function
arguments, as designated by ...
, may be specified using an abbreviated
function expression of the form .(...)
, cf. as_fn()
. If ...
is empty
or NULL
, then f
is simply returned.
reduce <- make_fn_aware(Reduce, "f") ## reduce() behaves just like Reduce() Reduce(function(u, v) u + 1 / v, c(3, 7, 15, 1, 292), right = TRUE) reduce(function(u, v) u + 1 / v, c(3, 7, 15, 1, 292), right = TRUE) ## reduce() can also interpret abbreviated function expressions reduce(.(u, v ~ u + 1 / v), c(3, 7, 15, 1, 292), right = TRUE)
reduce <- make_fn_aware(Reduce, "f") ## reduce() behaves just like Reduce() Reduce(function(u, v) u + 1 / v, c(3, 7, 15, 1, 292), right = TRUE) reduce(function(u, v) u + 1 / v, c(3, 7, 15, 1, 292), right = TRUE) ## reduce() can also interpret abbreviated function expressions reduce(.(u, v ~ u + 1 / v), c(3, 7, 15, 1, 292), right = TRUE)