4 ms·

I've been writing a bunch of Common Lisp recently, where I usually have been more interested in Schemes. I'm less bothered by its little inconsistencies, like

I've been writing a bunch of Common Lisp recently, where I usually have been more interested in Schemes. I'm less bothered by its little inconsistencies, like the empty list not needing to be quoted, than I used to be. Maybe because I'm getting older, and people develop cruft just like programming languages. I'm not really small and elegant anymore, so why should my Lisp be?

moonchild 5y ago
> I'm less bothered by its little inconsistencies, like the empty list not needing to be quoted, than I used to be CL certainly has its warts, but that is not one of them. Most data types other than pairs and symbols are self-evaluating. You don't quote number literals, for instance! That the list terminator is not self-evaluating is definitely a scheme wart. (Sadly, I'm told that motions to change this behaviour in r7rs-large were rejected.)
- JasonFruit 5y ago
  '(1 2 3) '(1 2) '(1) () ; wart
  - moonchild 5y ago
    That's syntax sugar and it's lying to you for convenience's sake. (+ . (1 . (2 . (3 . ())))) #| --> 6 |# (quote . (1 . (2 . (3 . ())))) #| --> (1 2 3) |# (1 2 3) is a pair and we have a rule for evaluating pairs: unless the car is a symbol denoting a special form (1 is not one such), apply the car to the cdr. So we need to quote it if we want to get it as a literal. () is a special list terminator object; it is not a pair—as this dotted list syntax shows—and it has neither car nor cdr, so our previous rule for evaluation does not apply. However we have another conventional rule: objects which are not pairs and are not symbols should evaluate to themselves. This applies to strings, characters, numbers, vectors... Why not to the list terminator?
    - JasonFruit 5y ago
      Never really thought that through. Thank you.
  - moonchild 5y ago
    Perhaps this makes it clearer: '(1 . (2 . (3 . ()))) '(1 . (2 . ())) '(1 . ()) () The ' applies to the ., not to the ().

moonchild 5y ago

> I'm less bothered by its little inconsistencies, like the empty list not needing to be quoted, than I used to be CL certainly has its warts, but that is not one of them. Most data types other than pairs and symbols are self-evaluating. You don't quote number literals, for instance! That the list terminator is not self-evaluating is definitely a scheme wart. (Sadly, I'm told that motions to change this behaviour in r7rs-large were rejected.)

JasonFruit 5y ago
'(1 2 3) '(1 2) '(1) () ; wart
- moonchild 5y ago
  That's syntax sugar and it's lying to you for convenience's sake. (+ . (1 . (2 . (3 . ())))) #| --> 6 |# (quote . (1 . (2 . (3 . ())))) #| --> (1 2 3) |# (1 2 3) is a pair and we have a rule for evaluating pairs: unless the car is a symbol denoting a special form (1 is not one such), apply the car to the cdr. So we need to quote it if we want to get it as a literal. () is a special list terminator object; it is not a pair—as this dotted list syntax shows—and it has neither car nor cdr, so our previous rule for evaluation does not apply. However we have another conventional rule: objects which are not pairs and are not symbols should evaluate to themselves. This applies to strings, characters, numbers, vectors... Why not to the list terminator?
  - JasonFruit 5y ago
    Never really thought that through. Thank you.
- moonchild 5y ago
  Perhaps this makes it clearer: '(1 . (2 . (3 . ()))) '(1 . (2 . ())) '(1 . ()) () The ' applies to the ., not to the ().