Functions without parentheses inside across()

[Luis]

Hi everyone,

I'm trying to track down some documentation about passing functions (without parentheses) and their arguments separately inside across(). This is my preferred way of using across() , over anonymous function/lambda notation, and I'm assuming it has something to do with using match.fun() internally.

I found this post and this issue, but I'm not sure if my interpretation is correct.

Any leads will be greatly appreciated.
Thanks!
LD

[technocrat]

Yeah, match.fun() doesn't consider functions with arguments as functions

is.function(mean)
#> [1] TRUE
is.function(mean(mtcars$mpg,na.rm = TRUE))
#> [1] FALSE

^{Created on 2021-01-01 by the reprex package (v0.3.0.9001)}

[Luis]

thanks!
does this mean that any arguments passed separately get pasted into the function elsewhere down the line?

[technocrat]

I can't quite follow the logic of match.fun

faux <- function (FUN, descend = TRUE)
{
  if (is.function(FUN))
    return(FUN)
  if (!(is.character(FUN) && length(FUN) == 1L || is.symbol(FUN))) {
    FUN <- eval.parent(substitute(substitute(FUN)))
    if (!is.symbol(FUN))
      stop(gettextf("'%s' is not a function, character or symbol",
                    deparse(FUN)), domain = NA)
  }
  envir <- parent.frame(2)
  if (descend)
    FUN <- get(as.character(FUN), mode = "function", envir = envir)
  else {
    FUN <- get(as.character(FUN), mode = "any", envir = envir)
    if (!is.function(FUN))
      stop(gettextf("found non-function '%s'", FUN), domain = NA)
  }
  return(FUN)
}

FUN <- function(x) mean(x, na.rm = TRUE)
faux(FUN)
#> function(x) mean(x, na.rm = TRUE)
!(is.character(FUN) && length(FUN) == 1L || is.symbol(FUN))
#> [1] TRUE
eval.parent(substitute(substitute(FUN)))
#> FUN
!is.symbol(eval.parent(substitute(substitute(FUN))))  
#> [1] FALSE

# on to else block
FUN <- function(x) x^2

# fails with as.character(FUN)
get(as.character(FUN), mode = "any", envir = envir)
#> Error in as.character(FUN): cannot coerce type 'closure' to vector of type 'character'

^{Created on 2021-01-01 by the reprex package (v0.3.0.9001)}