Arc Forumnew | comments | leaders | submitlogin
3 points by map 6142 days ago | link | parent

In Ruby, push appends to a list; unshift prepends:

  E:\>irb --prompt xmp
  lst = [3,4,5]
      ==>[3, 4, 5]
  lst.push( 6 )
      ==>[3, 4, 5, 6]
  lst.unshift( 2 )
      ==>[2, 3, 4, 5, 6]
  lst.pop
      ==>6
  lst.shift
      ==>2
  lst
      ==>[3, 4, 5]
  lst << 6
      ==>[3, 4, 5, 6]
  lst += [7]
      ==>[3, 4, 5, 6, 7]
  lst
      ==>[3, 4, 5, 6, 7]
NewLisp can insert in the midst of the list just as fast.

  > (set 'x '(0 1 2 3 4 5 6))
  (0 1 2 3 4 5 6)
  > (time (push 8 x 4) 99000)
  50
  > (set 'x '(0 1 2 3 4 5 6))
  (0 1 2 3 4 5 6)
  > (time (push 8 x 4) 99000)
  40
  > (set 'x '(2))
  (2)
  > (time (push 8 x) 99000)
  40
Ruby has the opposite problem from conventional Lisp: it appends quickly, but prepends slowly:

  t = Time.now; a=[2]; 99_000.times{ a.push( 8 ) }; p Time.now - t
  0.14
      ==>nil
  t = Time.now; a=[2]; 99_000.times{ a.unshift( 8 ) }; p Time.now - t
  70.902
      ==>nil
  t = Time.now; a=[0,1,2,3,4]; 99_000.times{ a.insert(2, 8) }; p Time.now - t
  73.346
That's 73 seconds! NewLisp can insert in a list 1800 times as fast as Ruby can!


1 point by absz 6142 days ago | link

Right. In Ruby, pushing, unshifting, and spliceing are all different operations, as they should be. Meaningful names are important.

It's not quite as fast to insert in the middle, but much faster than it should be. This would, to me, imply that newLISP isn't even using linked lists at all, but is instead using some form of array, which is decidedly unLispy. If that is the case (if, I say), then of course this will only work with "one reference only", as you can't construct lists which share cdrs; "one reference only" being an awful idea, I would consider the speed a fair tradeoff.

-----