Source code in the oberon-2 programming language

IMPORT Basic;
TYPE
	Node* = POINTER TO NodeDesc;
	NodeDesc* = (* ABSTRACT *) RECORD
		prev-,next-: Node;
	END;

	DLList* = POINTER TO DLListDesc;
	DLListDesc* = RECORD
		first-,last-: Node;
		size-: INTEGER;
	END;