Comment by kbp
8 years ago
> So why stick with the names of 704 registers? Was there a purpose to this?
Are there other, much better names for the two parts of a pair? First and second aren't great because they're not clear that it's a pair and not a larger sequence (and the difference is important in Lisp; since lists are built on conses, it would be odd to get the tail of a list by calling 'second'). The only other names I can think of would be something like left and right, but I don't think those would be substantially easier to understand for beginners than car and cdr.
When working with lists, many people prefer to use the functions first and rest, which behave identically to car and cdr but are more meaningfully named for list applications. They would be terrible names for the general cons-handling functions, though.
Left and Right are really commonly used in this situation in ML-descended languages. It’s not the worst thing.
I don’t mind car and cdr though. I kind of wish they were in Clojure tbh. It feels nice to pay tribute to a half-century of computing history.
> Left and Right are really commonly used in this situation in ML-descended languages. It’s not the worst thing.
Are you talking about Either types? OCaml and Haskell at least both call car and cdr fst and snd respectively, but they're rarely used.
As for left and right as names, I don't think they're any worse than car and cdr, I just don't think they're substantially better.
Would it be silly to use 'head' and 'tail' then?
I learned car/cdr in school so that's what I use.
I use FST and RST (for FIRST and REST). I like them because they are short, mnemonic, and can be composed like CAR and CDR, e.g. CADADDR = FRFRRST (though I also believe that if you find yourself doing this you're almost certainly doing something wrong).
In C++, I often use LHS and RHS (left hand side / right hand side). I know other people who like fst, eat (first, rest). Both seem better to me, as they have some meaning other than random made up strings (for people who don't use 704).
> Both seem better to me, as they have some meaning other than random made up strings (for people who don't use 704).
Calling the lefthand child of a node in a binary tree the "first" and the righthand child the "rest" seems like a markedly worse naming system than random made-up names, to me, because the use of English names seems to be implying meaning that it doesn't really offer.
The idea of a thing with two values, one on the left side and one on the right side is probably a bit more intuitive, but I really doubt it's that much moreso than just saying it has two parts called the car and the cdr. People who've never touched a 704 have been learning about conses as a data structure with two parts, a car and a cdr, for almost 60 years; to most of them, it's just vocabulary you learn now, the same way that numerator and denominator are just arbitrary names to people learning fractions.
I also think it's interesting how much people complain about car and cdr yet it's very rare that people complain about cons, which is just as badly named. It should probably have been called make-pair or something, which I think is a much bigger improvement than car vs lhs. But really, it's 3 words of vocabulary, whose definitions can be completely understood by
That's not very much to ask someone to wrap their head around, it was meaningful to the original implementors, and for people now there's about 60 years of precedent for using that terminology.
I feel the better question, and I don't know the answer, is does this kind of thing stop people taking up lisp. Honestly I think it does, for so many languages, the first view, the first 15 minutes of reading, and the first 10 hours are super important, that is when you lose many possible users. It is certainly the points where I often drop languages.
While lisp is old, it's never picked up many users. This is the kind of little thing which makes me not want to teach it (not just this, but just lots of little ways it seems stuck in history).
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