rlp.pl

use 5.010;
use strict;
use warnings;
use List::MoreUtils qw/natatime zip/;
my $rlp  = [ 1, 2, [3, 4, [5, 6]]];
my $rlp1 = [ 1, 2, [3, 4, [5, 6]]];
my $rlp2 = [ 1, 2, [3, 4, [5, 9]]];

sub rcmp {
    my ($l, $r, $test) = @_;
    if (!(ref $l || ref $r)) {
        return $test->($l, $r);
    }
    elsif ((ref $l && ref $r) && (ref $l eq ref $r))  {
        return 0 if @$l != @$r;
        my $it = natatime 2, zip(@$l, @$r);
        while ( my($x, $y) = $it->() ) {
            my $rv = rcmp($x, $y, $test);
            return 0 unless $rv;
        }
        return 1;
    }
    else {
        return 0;
    }
}

say rcmp($rlp, $rlp1, sub { $_[0] == $_[1] });
say rcmp($rlp, $rlp2, sub { $_[0] == $_[1] });