#! /usr/bin/env raku

unit sub MAIN ($values = "1 2 3 4", :z($zero));

my @values = $values.words;

$zero
  ?? ( die "Must be 0..9 only" unless all(@values) ~~ /^<[0..9]>$/ )
  !! ( die "Must be 1..9 only" unless all(@values) ~~ /^<[1..9]>$/ );

class LinkedList
{
  has Int        $.value;
  has LinkedList $.next is rw;
  
  method add-elems (@values is copy)
  {
    my $list  = self;
    my $first = @values.shift;
    my $obj   = LinkedList.new(value => $first);

    ($list ~~ LinkedList:D)
      ?? ( $list.next = $obj )
      !! ( $list      = $obj );

    $obj.add-elems(@values) if @values.elems;

    return $obj;
  }

  method recursive-value
  {
    return flat(self.value, self.next.recursive-value) if self.next;
    return self.value;
  }
}

my $ll = LinkedList.add-elems(@values>>.Int);

say $ll.recursive-value.join(" -> ");