#!/usr/bin/perl
use strict;
use Data::Dump 'dd';

my $tree =
[
    1, [[2, 3], [4, [[[5, 6], [7, 8]], [9, 10]]]]
];

#my $T = get_tree_iterator($tree);
#my $T = get_tree_iterator_explicit($tree);
#my $T = get_tree_iterator_2($tree);
my $T = get_tree_iterator_2_explicit($tree);

while (my $leaf = $T->()) {
    print "leaf: $leaf\n";
}

sub get_tree_iterator {
    my @stack = (shift);
    return sub {
        print "---\n";
        dd \@stack;
        while (@stack and ref $stack[0] eq 'ARRAY') {
            unshift @stack, @{shift @stack};
            dd \@stack
        }
        return shift @stack;
    }
}

sub get_tree_iterator_explicit {
    my @stack = (shift);
    return sub {
        print "---\n";
        dd \@stack;
        while (@stack and ref $stack[0] eq 'ARRAY') {
            print "  split tree into left & right\n";
            unshift @stack, @{shift @stack};
            dd \@stack
        }
        return shift @stack;
    }
}

sub get_tree_iterator_2 {
    my @rtrees = (shift);
    my $tree;
    return sub {
        $tree = pop @rtrees;
        print "---\n";
        print "tree: "; dd $tree;
        print "rtrees: "; dd \@rtrees;
        ($tree, $rtrees[@rtrees]) = @$tree while ref $tree;
        return $tree;
    }
}

sub get_tree_iterator_2_explicit {
    my @rtrees = (shift);
    my $tree;
    return sub {
        $tree = pop @rtrees;
        print "---\n";
        print "tree: "; dd $tree;
        print "rtrees: "; dd \@rtrees;
        while (ref $tree) {
            print "traverse L\n";
            ($tree, $rtrees[@rtrees]) = @$tree;
            print "  tree: "; dd $tree;
            print "  rtrees: "; dd \@rtrees;
        }
        return $tree;
    }
}