Make Function Arguments Explicit

Transform function calls in R source code so that all arguments are passed with explicit parameter names.

The transformation is a minimal, position-based text edit: only the missing argument = prefixes are inserted into the original source. Everything else is preserved verbatim, including comments inside function bodies, blank lines, indentation and operator spacing.

If the function has a ... formal, positional arguments that are captured by ... are left in place as-is. Calls that forward ... literally (e.g. g(...)) are skipped, because the number of arguments that ... expands to cannot be known statically.

Operators (+, -, *, /, etc.), subset operators ([, [[, $), assignment (<-, =, <<-), and special syntax (if, for, while, repeat, {, (, function) are not transformed.

Usage

package_func_arg_explicit(path = NULL, skip_functions = NULL, ...)

make_func_arg_explicit(path = NULL, skip_functions = NULL, ...)

Arguments

path

Path to an R file to modify. If NULL and RStudio is available, the active document path is used.

skip_functions

Optional character vector of function or operator names to skip during transformation (e.g. c("my_special_fn")). In addition to user-provided names, all built-in operators (+, -, etc.), special syntax forms (if, for, {, etc.), and all %...% infix operators (%in%, %>%, %||%, etc.) are always skipped automatically.

...

Additional arguments. Currently unused and must be empty.

Value

Invisible NULL, called for its side effect of writing the transformed code back to the file.

Functions

• package_func_arg_explicit(): Processes all .R files in a package's R/ directory, making function arguments explicit.

Pipes and placeholders

The right-hand side of a pipe receives an extra argument from its left-hand side, so that argument is counted during positional matching: x %>% str_remove("a") becomes x %>% str_remove(pattern = "a"), because the piped-in data already fills the first formal (string).

Placeholders are honoured. When a native pipe (|>) uses the _ placeholder, the piped value fills the formal named next to _, so no leading argument is pre-claimed and the remaining positional arguments are still matched: x |> lm(y ~ z, data = _) becomes x |> lm(formula = y ~ z, data = _). When a magrittr pipe (%>%, %<>%, %T>%) contains . anywhere in its right-hand side, the piped value is substituted at . instead of being inserted as the first argument, and again no formal is pre-claimed: x %>% f(., y) becomes x %>% f(a = ., b = y).

Single-file operation

Operates on one R file. When path is NULL and RStudio is available, the currently active document is used automatically.

Examples

# \donttest{
tf <- tempfile(fileext = ".R")
writeLines("vapply(1:9, function(x) x*2, numeric(1))", tf)
make_func_arg_explicit(tf)
#> ✔ Made function arguments explicit in /tmp/RtmpWnqw2p/file1aa5612b3ff5.R
cat(readLines(tf), sep = "\n")
#> vapply(X = 1:9, FUN = function(x) x*2, FUN.VALUE = numeric(length = 1))
# vapply(X = 1:9, FUN = function(x) x*2, FUN.VALUE = numeric(length = 1))
# }