Arc Forumnew | comments | leaders | submitlogin
1 point by greatness 6116 days ago | link | parent

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.