as_fn: Abbreviated functional arguments

In nofrills: Low-Cost Anonymous Functions

Abbreviated functional arguments

Description

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).

Usage

as_fn(.f)

Arguments

.f	A function or an abbreviated anonymous-function expression of the form .(...), where ... is a function declaration (i.e., . (dot) in this context is an alias of fn()). Quasiquotation is supported.

Details

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).

Value

If .f is a function, it is simply returned, otherwise the function determined by the function declaration is returned.

See Also

fn(), make_fn_aware()

Examples

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)

nofrills documentation built on March 18, 2022, 7:40 p.m.