MODE ELEMENT = STRING;
MODE NODE = 
  STRUCT ( ELEMENT value, REF NODE next );
MODE LIST = REF NODE;
LIST empty = NIL;
PROC append = ( REF LIST list, ELEMENT val ) VOID:
BEGIN
  IF list IS empty
  THEN
    list := HEAP NODE := ( val, empty )
  ELSE
    REF LIST tail := list;
    WHILE next OF tail ISNT empty
    DO
      tail := next OF tail
    OD;
    next OF tail := HEAP NODE := ( val, empty )
  FI
END;