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From: pbiron@weber.ucsd.edu (Paul Biron)
Newsgroups: comp.sys.mac.hypercard
Subject: an exists(object) function ?
Keywords: HyperTalk
Message-ID: <2308@network.ucsd.edu>
Date: 25 Mar 90 23:21:42 GMT
Sender: nobody@network.ucsd.edu
Reply-To: pbiron@weber.ucsd.edu (Paul Biron)
Organization: Division of Social Sciences, UCSD
Lines: 52

One of the most annoying things about HyperTalk
is that there is no exists() function.  By this
I mean something that could be used in the 
following mannor :

on foo
    repeat with cardNum = 1 to the number of cards
        if exists("card button bar") then
            set the rect of card button bar to 100,200
        else
            put "card button bar does not exist on" && -|
            the long name of this card
    end repeat
end foo

Sure, this can be simulated by :

function exists object
    put word 3 to word the number of words in -|
    object of object into objectName

    if word 1 of object is "card" then
        if word 2 of object is "button" then
            repeat with i = 1 to the number of card buttons
               if the short name of card button i -|
               is objectName then
                   return true
           end repeat
        else if word 2 of object is "field" then
           ...
    else
        ....
end exists

but this is highly inefficient, and not very general
(what about "cd btn bar", "btn number X", etc.).

Does anyone know of a better way to do this?
Perhaps an XFCN?  My first guess is that there
is no such external, since the file structure
of stacks has not been made public, and one
would have to be reading the file structure
to do something like this.

I know its too late, but my wish list for the
next release of HyperCard contains such a function.


Paul Biron     (pbiron@ucsd.edu)       (619) 534-5758
Social Sciences DataBase Project, Central University Library
University of California, San Diego
La Jolla, Ca. 92093