Fun fact, R also has -> (assign to the RHS instead of LHS), and "super-assignment" <<- and ->>, and also can use = sometimes too (and I think has different semantics). Yay R.
> also can use = sometimes too (and I think has different semantics)
That’s a common misconception (even the official documentation is misleading).
In reality, assignment `<-` and assignment `=` have the exact same semantics (except for precedence, and unless you redefine them, which you can). The confusion comes from the fact that the `=` symbol is syntactically overloaded: it is also used for named argument passing (`foo(x = 1)`). This leads people to falsely claim that, if you wanted to perform assignment in a function call (which occasionally makes sense in R), then you’d have to use `<-`. But this is false. You merely need to disambiguate the usage, e.g. with extra parentheses: `foo((x = 1))` works.
FWIW, that's what Ross Ihaka does as well (or at least did in a presentation that I watched - and pointed out that you can use = for assignment). Personally, I think = for assignment is a disaster, and wish I could use <- and -> in every language.
I've used R since it was in beta form, and one of the most interesting things to me (aside from the evolution of type hierarchy) has been changes in use of the assignment operator.
When I started, = was the norm for assignment, with == for evaluating equality. Later I started noticing that people were recommending <- based on scope concerns, but it was kind of subjective preference. Now I see articles like this saying that the "preferred use" is <-, and some people don't even know about =.
I agree = versus == can lead to tricky errors in code, but I still prefer = for various reasons in general in languages (although I get the scope arguments).
The reason is that = is shorter, and assignment is an definitional equality, which to my impression is the whole point of programming in general usually. As others have suggested here, between = and ==, = is by far the more commonly used operator in meaning, so to me it makes sense to use = for succinctness.
In math, there is an "equal by definition" operator, with three lines, so I could see that, but keyboards don't have that, so it's more steps. := is also a kind of standard "by definition" usage as discussed in the article, but again, it's more steps. I'd still prefer that over <- in R.
Interesting. I started using it in 2000 and was working directly with members of R-core at the time. My experience was that the only time I ever saw = used was by DTL.
It really wasn’t until Google published their style guide and then later when Hadley published his that I started seeing = in heavy usage.
To your point about = being shorter I wonder if the difference was that a lot of the folks I interacted with were using Emacs with ESS which would interpolate _ to <- so they wouldn’t have noticed? Just a theory.
Either way I was taught from some of the R creators that <- was evil and to be avoided. It wasn’t until I stopped using R regularly that I switched, it became too mentally taxing to change assignment operators when I bounced between languages
I teach R, and most of the students have never programmed before, at least not anything other than having been exposed to a configuration file or writing a little html.
x = x+1 is really confusing because of the way kids learn math. The notation x <- x+1 at least conveys the idea of taking a value and storing it somewhere.
In the original Smalltalk implementation, the character corresponding to _ in ASCII was a left facing arrow, which Smalltalk used for assignment at the time.
"In the original Parc Place image, the glyph of the underscore character (_) appeared as a left-facing arrow (like in the 1963 version of the ASCII code). Smalltalk originally accepted this left-arrow as the only assignment operator. Some modern code still contains what appear to be underscores acting as assignments, hearkening back to this original usage. Most modern Smalltalk implementations accept either the underscore or the colon-equals syntax."
