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1 point by drcode 6116 days ago | link | parent

Well, I'd be happy with that, except it doesn't work- There's no way to know with or.a.b if you're at the end of the list or if there's just a nil as a last item in the list. Notice the missing item here:

  > (do (print-list '(nil nil nil)) 1)
  nil
  nil
  1


1 point by greatness 6116 days ago | link

Ah, I see. When destructuring the arguments, if the last argument is nil it is equivalent to not being an item. ie:

  arc> (= a '(1 2 nil))
  (1 2 nil)
has a last destructuring bind of (nil . nil) so 'a would be nil and 'b would be nil, making my code not work and making it impossible to differentiate between the end of the list and the list with a last item of nil.

Even so, it's not that much of a problem:

  (def print-list (args)
    (unless no.args
       (prn:car args)
       (print-list:cdr args)))
This code shares almost the same amount of brevity, though I believe it defeats the purpose of what you were trying to do with the destructuring bind (make the calls to car/cdr disappear).

I don't believe your solution is the right thing to do because it wouldn't make sense for the car to be optional and then not force the cdr to be optional. I do not believe an optimal destructuring solution exists that could improve on the brevity of the original car/cdr solution.

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