Can anyone well versed in lisp explain this joke to me? I've done some reading on functional programming languages and know that CAR/CDR mean Contents of Address/Decrement Register but I still don't really understand the humour.
90
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start "scheming around" a bit and then you'll understand. hahaha. it's better than a bumper sticker that says "this programmer stops at all garbage collections."
- gonzobrains
Approximately half an hour after this question was linked to from news.ycombinator.com/item?id=14416846 it was put on hold. It's an 8 year old question. Annoyingly, I can't argue against the on-hold status but I don't like the vibe of putting it on hold now.
- i336_
@i336_ per the meta discussion, it is closed to prevent new answers from clogging up the review queue.
- Andrew
Aren't there any other hold reasons? Opinion-based is... wrong
- Entendu
Shouldn't it be Protected instead?
- Federico klez Culloca
3 Answers
136
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In Lisp, a linked list element is called a CONS. It is a data structure with two elements, called the CAR and the CDR for historical reasons. (Some Common Lisp programmers prefer to refer to them using the FIRST and REST functions, while others like CAR and CDR because they fit well with the precomposed versions such as (CADR x) ≡ (CAR (CDR x)).
The joke is a parody of the bumper stickers you sometimes see on beat-up old cars saying "My other car is a Porsche/BMW/etc."
My response to this joke has always been "My other CAR is a CADR. CDR isn't a CAR at all."
34
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Yes, definitely a geek joke.
The names come from the IBM 704, but that's not the joke.
The joke is (bad) pun on "my other car is a ___." But the in-joke is about recursion.
When you loop/manipulate/select/invoke/more in lisp you use a combination of car (the first element in the list) and cdr (the rest of the list) to juggle functions.
So you've got a car, but your other car is your cdr because you can always get a car from a cdr since the cdr is always (in recursion) more elements. Get it? Laugh yet?
You'll probably have to learn lisp to actually chuckle a bit, or not. Of course, by then, you'll probably find yourself chuckling randomly for no apparent reason because:
Lisp makes you loopy.
