Arc Forumnew | comments | leaders | submitlogin
1 point by shader 2825 days ago | link | parent

Yes, it does seem kind of fuzzy. And I doubt it would actually be the reader doing that, more likely the 'list function would be the source for the extra nils

However, you need some way to distinguish between a list in the car, and the next element in a chain. The only way to do that is to have it be in the car of a cons cell, and the only way to do that is to have something else in the cdr. If you don't have anything after the list, you have to fill it with nil.

5 points by rocketnia 2825 days ago | link

The only way to do that is to have it be in the car...

Actually, you could have a special symbol '! in the car in order to identify that the cdr is actually supposed to be the last element. Then (a b c (d e f)) is represented as (a . (b . (c . (! . (d . (e . f)))))), i.e. (a b c ! d e f). Banged lists. ;)

In fact, having the symbol be a colon might even make it a nice optional style:

  (accum acc
    (each x args
      (acc (* 2 x))))
  (accum acc :
     each x args :
       acc : * 2 x)    ; reminiscent of Arc's (acc:* 2 x)
It's just that you never get to observe the ': from within code. There might be gotchas when generating code, too: The expression (quote : ) would evaluate to nil, huh? XD


3 points by evanrmurphy 2825 days ago | link

Dear rocketnia,

Some of your ideas are very bizarre. I mean this as a compliment. Please keep 'em coming. :)

Regards, evanrmurphy