tl;dr

I present you a function that warns if an R script contains The Assignment Operator That Shall Not Be Named.

Assign of the times

So, it’s been confirmed with extremely robust and objective evidence: the left-assignment arrow (x <- 1) is better than equals (x = 1) for assignment in R.¹

So, unless you hate democracy, you should protect yourself from aberrant code that uses the cursed symbol.

But what if a nefarious colleague still sends you their scuffed code?

Assignment refinement

I’ve created the appraise_assignment() function that will peek at a suspect script and warn you if it contains the foul mark.

appraise_assignment <- function(file, destroy = FALSE) {
  
  tokens <- getParseData(parse(file))[["token"]]
  
  if (any(tokens == "EQ_ASSIGN")) {            # if '='
    warning("\nme = 'disgusted'") 
    if (destroy == TRUE) {
      answer <- readline("Destroy file? y/n: ")
      if (answer == "y") cat("Have mercy! This time...")
    }
  } else if (any(tokens == "RIGHT_ASSIGN")) {  # if '<-'
    cat("'unorthodox' -> you\n")
  } else if (any(tokens == "LEFT_ASSIGN")) {   # if '->'
    cat("you <- 'hero'\n")
  } else {
    cat("anyway(assignment(is(even('what'))))\n")
  }
  
}

Basically, we parse() an input file and then the function uses getParseData() to extract ‘tokens’ (i.e. maths symbols, special operators, variables, etc) from the R expressions within.

In particular, it spots the token called EQ_ASSIGN, which is when = is used in the context of assignment.

I saw the assign

For demonstration purposes, I’ve written four temporary files containing left assign (<-), right assign (->), equals (=), and no assignment at all.² Our function will catch even a single deviation in a given file.

temp <- tempdir()  # temp location to store files

purrr::walk2(
  c("x <- 1", "x <- 1; y -> 1", "x <- 1; y = 1", "x"),
  c("left", "right", "equals", "none"),
  ~writeLines(.x, file.path(temp, paste0(.y, ".R")))
)

list.files(temp, pattern = ".R$")

## [1] "equals.R" "left.R"   "none.R"   "right.R"

First, let’s pass the file containing the unquestionably correct assignment operator.

appraise_assignment(file.path(temp, "left.R"))

## you <- 'hero'

Right-assignment is left-assignment’s less-handsome sibling.

appraise_assignment(file.path(temp, "right.R"))

## 'unorthodox' -> you

Hold steady…

appraise_assignment(file.path(temp, "equals.R"))

## Warning in appraise_assignment(file.path(temp, "equals.R")): 
## me = 'disgusted'

Phew, we got a warning, so we know the file is dangerous and should never be opened.

In fact, if you set the argument destroy = TRUE in appraise_assignment(), you’ll be prompted to irrecoverably annihilate the rotten file forever.³

For completeness, is it really an R script if it doesn’t contain any assignment at all?

appraise_assignment(file.path(temp, "none.R"))

## anyway(assignment(is(even('what'))))

Assigning off

In conclusion, some assignment operators were created more equal than others. See Colin Fay’s round-up to learn more about the history and plethora of these symbols (and be happy that the underscore is no longer legitimate).

Anyway, welcome to the best timeline, where we all recognise <- unequivocally as the champion and = can get absolutely rekt.

If I had one wish though, it would be to make the left-assign arrow even more powerful. How about making it really long? 23 hyphens seems sufficiently dominant.

x <----------------------- 1
x

## [1] 1

It’s a really long arrow, so I call it ‘the spear’.⁴ I look forward to its adoption by R Core.

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