In attempting to formulate another reply to this little game of golf, I've hit upon some rather peculiar behaviour in list expression evaluation order. Consider the following recursive code: 
  sub li {
    shift;
    @_ ? (scalar @_, &li) : ();
  }
  print li qw(a b c d e f g);   # prints 654321

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So far so good... now substitute $#_ + 1 for scalar @_: 
  sub li {
    shift;
    @_ ? ($#_ + 1, &li) : ();
  }
  print li qw(a b c d e f g);   # prints 654321

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Que bueno! Moving on, lets remove the "+1" ... 
  sub li {
    shift;
    @_ ? ($#_, &li) : ();
  }
  print li qw(a b c d e f g);   # prints -1-1-1-1-1-1

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What is this? Apparently, $#_ is now evaluated after the recursive call. To my eyes, this is a rather unexpected result, especially when you consider how the comma operator behaves in a scalar context, and my first two examples. This phenomenon affects globals as well: 
  use vars '$x';
  sub li {
    $x = shift;
    @_ ? ($x, &li) : ();
  }
  print li qw(a b c d e f g);   # prints gggggg

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Update: remarkably, I've just determined that this behaviour is tied to the way in which the subroutine call is performed: if the calls above are switched from &li to li(@_), the order of evaluation goes back to normal. How wierd!
Update2: actually, the above only works for the $#_, but not the globals. Stranger and stranger...

In reply to !@#$ $#_ by MeowChow

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