infocom/compilers/inform6/library/contributions/chooo.h

! Chooo.h by Krister Fundin (fundin@yahoo.com)
!
! This is an object oriented extension to the ChooseObjects entry point.
! Adopting it only requires a couple of simple steps:
!
!   1. In your ChooseObjects routine, start by generating a default return
!   value. If you, for instance, want to exclude scenery from "all" lists,
!   then this could be done here. If you don't want to make any such global
!   decisions, just choose a default of 0 if the "code" argument is 0 or 1,
!   or a number like 5 if the code is 2.
!
!   2. Add this line to the end of your ChooseObjects routine:
!
!      return ChooseObjectsOO(code, default);
!
!   where the second argument is the default value you decided on earlier.
!
!   3. In any object or class for which you want to return something else
!   than the default value, give it one of the methods choose_noun(),
!   choose_second() or choose_multi().
!
!         choose_noun()
!   Is called when the code is 2 and the object under consideration is a
!   noun. Return 1 to 9 or false to not make a decision.
!
!         choose_second(noun)
!   Is called when the code is 2 and the object under consideration is a
!   second. The noun is given as the first argument. Return 1 to 9 or false
!   to not make a decision.
!
!         choose_multi(code)
!   Is called when code is 0 or 1. The code is passed as the first argument.
!   Return 1 to force the object to be included in the "all" list, 2 to
!   force it to be excluded, or false to not make a decision.
!
!   These three methods are all additive. If an object returns false, and
!   one of its superclasses has its own method, that superclass is asked to
!   do the same decision. If it also returns false, the process is repeated.
!   If no decision is made, the default value supplied to ChooseObjectsOO()
!   is returned. You can also force the default value to be chosen by
!   returning -1 from any of these methods.
!
!   In all three methods, you can use action_to_be to check the action. It
!   is also possible to use the same implied switch syntax as in before and
!   after routines.
!
!   As you can see, the object oriented interface doesn't completely replace
!   the old entry point interface but rather augments it. First, a decision
!   is made on a global level, then the object has a chance to override that
!   decision.
!
!         Krister Fundin, 2005

property additive choose_noun;
property additive choose_second;
property additive choose_multi;

[ ChooseObjectsOO obj code default par ret s;
   ! set the action for easy switching
   s = action;
   action = action_to_be;

   ! check if we have reversed grammar
   if (action_reversed)
      par = 1-parameters;
   else
      par = parameters;

   ! call the appropriate method
   if (code == 2)
   {
      if (par == 0)
         ret = obj.choose_noun();
      else
         ret = obj.choose_second(inputobjs-->2);
   }
   else
   {
      ret = obj.choose_multi(code);
   }

   ! restore old action
   action = s;

   ! uncomment for debugging
   !print (name) obj, ": code = ", code, ", ret = ", ret,
   !      ", default = ", default;
   !new_line;

   ! if we have a value, return it, else return the default
   if (ret && ret ~= -1)
      return ret;
   else
      return default;
];