! >GL  The following example, suggested to the author by Richard Tucker,
!      demonstrates an apparently tricky case of objects with associated
!   sub-objects.  The pair of white gloves behaves just like any other item
!   of clothing - but the player can also use the left and right gloves
!   independently, can take away or wear only one and so on.  When they
!   come back together (even in a cupboard, say, or on a mantelpiece)
!   they are called a pair again.
!
!   We can do this with only three objects, one daemon and one rule.
!   
!   When the gloves are together, and the player refers to an individual
!   glove, the before rule splits up the pair and starts the daemon.
!   Once active, the daemon tries every turn to re-join them into a pair.
!   (If it succeeds, it turns itself off.)
!
!   Note that the "pair of gloves" object has the "general" attribute exactly
!   when the gloves are apart.  Otherwise the pair-object contains both
!   glove objects, and has "transparent" so that the parser knows the player
!   can see and refer to them.
! ----------------------------------------------------------------------------

Object -> gloves "white gloves"
  with article "a pair of",
       name "white" "gloves" "pair" "of",
       daemon
       [;  if (parent(right_glove) ~= parent(left_glove)) return;
           if ((left_glove has worn && right_glove hasnt worn)
               || (left_glove hasnt worn && right_glove has worn)) return;
           if (left_glove has worn) give gloves worn; else give gloves ~worn;
           move gloves to parent(right_glove); give gloves ~general;

           move right_glove to gloves; move left_glove to gloves;
           give right_glove ~worn;     give left_glove ~worn;
           
           StopDaemon(self);
       ],
  has  clothing transparent;

Class  Glove
  with article "the",
       name "white" "glove",
       before
       [;  if (self notin gloves) rfalse;
           move left_glove to parent(gloves); move right_glove to parent(gloves);
           if (gloves has worn)
           {   give left_glove worn; give right_glove worn;
           }
           give gloves general; remove gloves;
           StartDaemon(gloves);
       ],
  has  clothing;

Glove -> -> left_glove "left glove"
  with description "White silk, monogrammed with a scarlet R.",
       name "left";
Glove -> -> right_glove "right glove"
  with description "White silk, monogrammed with a scarlet T.",
       name "right";

! ----------------------------------------------------------------------------
!   ...and that's all: the "gloves" code is self-contained.
!
!   Exercise for the reader: hide a (sharp) jewel inside the left glove.
!     (Alter the glove class to make them containers open only when not worn.
!      Add two "after" rules to warn the player if there's something sharp
!      to the touch, one for putting on the pair of gloves, one for putting on
!      an individual glove.)
! ----------------------------------------------------------------------------


! ----------------------------------------------------------------------------