The basic data structure of LISP.

class Cons {

 /** The head of the cons. */
 dynamic _head;

 /** The tail of the cons. */
 dynamic _tail;

 /** Constructs a cons. */
 Cons(this._head, this._tail);

 /** Accessors for the head of this cons. */
 dynamic get head => _head;
 set head(dynamic head) => _head = head;

 /** Accessors for the tail of this cons. */
 dynamic get tail => _tail;
 set tail(dynamic tail) => _tail = tail;

 /** Compare the cells. */
 bool operator ==(Cons cons) {
   return cons is Cons && head == cons.head && tail == cons.tail;
 }

 /** Returns the string representation of the cons. */
 String toString() {
   var buffer = new StringBuffer();
   buffer.write('(');
   var current = this;
   while (current is Cons) {
     buffer.write(current.head.toString());
     current = current.tail;
     if (current != null) {
       buffer.write(' ');
     }
   }
   if (current != null) {
     buffer.write('. ');
     buffer.write(current);
   }
   buffer.write(')');
   return buffer.toString();
 }

}