use warnings;
use strict;

nested_for(
          [[1..2], ['a'..'c'], ['A'..'D']],
           sub {print "Printing! [@_]\n";}
);

my $i = nested_for([[qw(r o y)],sub{[$_]}, [qw(b i v)]]);
my @args;
print "@args\n" while @args = $i->();

# Handles the coderef arg, if any
sub nested_for {
    my @loops = @{shift()};
    if (@_) {
        my $fn = shift;
        my @args;
        my $i = ret_iter(@loops);
        $fn->(@args) while @args = $i->();
    }
    else {
        return ret_iter(@loops);
    }
}

# Turns a list into a self-resetting iterator
# (upon completing iterations, it returns empty-list, then
# the next iteration is back at the beginning)
sub mk_iter {
    my $ref = $_[0];
    my $i = 0;
    return sub {
        my @items;
        @items = @{(ref $ref eq 'CODE') ? $ref->() : $ref}
          unless @items;
        if ($i > $#items) {
            $i = 0;
            @items = @{$ref->()} if ref $ref eq 'CODE';
            return ();
        } else {
            return $items[$i++];
        }
    }
}

# Like map for two iterators, returning an iterator
sub nest {
    my ($outer, $inner) = @_;
    my @out = $outer->();
    return sub {
        local $_ = $out[$#out];
        my @in = $inner->();
        unless (@in) {
            return unless @out = $outer->();
            $_ = $out[$#out];
            @in = $inner->();
        }
        return (@out, @in);
    };
}


use List::Util 'reduce';
sub ret_iter {
    reduce {nest($a, $b)} map mk_iter($_), @_;
}