sub list_iter {
   my @list = @_;
   return sub {
      return @list ? shift(@list) : ();
   };
}

my $iter = list_iter('a', 1, '', 0, undef, -1);
while( my ($next) = $iter->() ) {
   print( $next // '[undef]', "\n" );
}

##</code><code>##

sub list_iter {
   my @list = @_;
   return sub {
      return 0 if !@list;

      $_[0] = shift(@list);
      return 1;
   };
}

my $iter = list_iter('a', 1, '', 0, undef, -1);
while( $iter->( my $next ) ) {
   print( $next // '[undef]', "\n" );
}

##</code><code>##

a
1

0
[undef]
-1