Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!uwm.edu!rpi!zaphod.mps.ohio-state.edu!samsung!uunet!brunix!vali!man
From: man@vali.cs.brown.edu (Mark H. Nodine)
Newsgroups: comp.sys.mac.hypercard
Subject: Re: Checking for card existance?
Keywords: HyperCard, Booga-Booga-Booga
Message-ID: <38641@brunix.UUCP>
Date: 3 May 90 17:57:02 GMT
References: <903@gistdev.gist.com>
Sender: news@brunix.UUCP
Reply-To: man@vali.cs.brown.edu (Mark H. Nodine)
Organization: Brown Computer Science Dept.
Lines: 27

In article <903@gistdev.gist.com>, andy@gistdev.gist.com (Andy Warinner)
writes:
|>
|>I have a field that stores the id of a card.  Is there any way to 
|>check that the id stored actually exists?  For example:
|>
|>	-- bkgnd field "cardPtr" holds card id
|>	if verifyCard(bkgnd field "cardPtr")
|>		then go to card id (bkgnd field "cardPtr")
|>		else answer "You screw up!"

How about

function verifyCard theID
   put the short id of this card into cardID
   push this card
   go card id theID
   put (the short id of this card is not cardID) into answer
   pop card
   return answer
end verifyCard

I just made this up on the spot, but I know the technique works, since
I've used it before.  In other words, the code may be flawed, but the
technique is OK.

	--Mark