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<HTML><HEAD><TITLE>Answer to Exercise 86</TITLE></HEAD>
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<BODY BGCOLOR="#FFFFFF">
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<TABLE><TR><TD Valign="top"><IMG SRC="../icons/exercise.gif" ALT="??"><TD bgcolor="#FAA89B"><B>ANSWER TO EXERCISE 86</B><TR><TD><TD>
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The label object itself is not too bad:
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Object -> label "red sticky label"
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with name "red" "sticky" "label",
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{ print "(first removing the label from ",
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(the) self.number, ")^"; self.number=0; move self to player;
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if (second==self) "That would only make a red mess.";
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self.number=second; remove self;
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print_ret "You affix the label to ", (the) second, ".";
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[ x; x=self.number; if (x==0) rfalse;
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Look: if (x in location)
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print "^The red sticky label is stuck to ", (the) x, ".^";
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print "^The red sticky label is stuck to ", (the) x, ".^";
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[; if (parent(self)~=0) self.number=0; ];
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Note that <TT>label.number</TT> holds the object the label is stuck to, or
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0 if it's unstuck: and that when it is stuck, it is removed from the
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object tree. It therefore has to be moved into scope, so we need the
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rule: if the labelled object is in scope, then so is the label.
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[ InScope actor i1 i2;
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if (label.number==0) rfalse; if (disable_self==1) rfalse;
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i1 = TestScope(label, actor);
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i2 = TestScope(label.number, actor);
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if (i2~=0) PlaceInScope(label);
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This routine has two interesting points: firstly, it disables itself
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while testing scope (since otherwise the game would go into an endless
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recursion), and secondly it only puts the label in scope if it isn't
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already there. This is just a safety precaution to prevent the label
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reacting twice to actions (and isn't really necessary since the label
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can't already be in scope, but is included for the sake of example).
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<HR>Back to <A HREF="../section28.html#ex86">the exercise in section 28</A><HR>
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<SMALL><I>Mechanically translated to HTML from third edition as revised 16 May 1997. Copyright © Graham Nelson 1993, 1994, 1995, 1996, 1997: all rights reserved.</I></SMALL></BODY></HTML>
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