#! perl
use v5.14;;
use Data::Dump qw[ pp ];

sub genNested {
    my $n = shift;
    map{ rand() < 0.5 ? [ rand(1000), genNested( $n-1 ) ] : rand( 1000 ) } 1 .. $n;
}

my @nested = genNested 3;
pp \@nested;

my @flat = 1..10;

sub genIterator(+)
{
  my $array = shift;
  my $index = 0; # Current index in the list
  my $child;  # Iterator for the level below if the current element is an array
  return sub { 
    my $element;  
    if (defined $child)
    {
      $element = $child->();
    }
    if (!defined $element)
    {
      $child = undef;
      $element = $index < @$array ? $array->[$index++] : undef;
      if (ref $element eq 'ARRAY')
      {
        $child = genIterator($element);
        $element = $child->();
      }
    }
    return $element;
  }
}

my $next = genIterator @nested;
say while $_ = $next->();