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From: akcs.joehorn@hpcvbbs.UUCP (Joseph K. Horn)
Newsgroups: comp.sys.handhelds
Subject: Re: HP 48 Faster PGDIR
Message-ID: <2850bd41:3374.4comp.sys.handhelds;1@hpcvbbs.UUCP>
Date: 8 Jun 91 11:40:08 GMT
References: <284dca48:3374comp.sys.handhelds@hpcvbbs.UUCP> <25590171@hpcvra.cv.
Lines: 42

Bill Wickes writes that running my FPGDIR after recalling objects from
the target directory to the stack can cause problems.

Wow!  That's for sure!  I just tried it, and the very first attempt
tanked everything in the machine.

Rats.  The moral here is twofold:

(1) The obvious: don't use FPGDIR unless you KNOW FOR SURE that there are
no references to objects that will be left floating in limbo.

(2) Less obvious: Be Careful When You Hide Objects In Directories!  Many
articles and programs about "hiding" things have floated down this
bitstream, and not once did anybody mention that hiding things in
directories can send the 48 out to lunch.  But if ALL the items in a
directory are hidden, it's an accident waiting to happen.  Because then
simply PURGEing the directory (if there are any memory references to its
contents) will cause problems at the next garbage collection.

The first moral is worded with "unless" because the situation is exactly
the same for the new 256K and 512K bankswitched cards now available for
the 48.  I just played with a 512K card tonight at the 48 Club meeting in
L.A., and it has a BANKN function that allows you to bank switch WITHOUT
PERFORMING A SYSTEM HALT.  The owner's manual clearly states that doing
this while there are any memory references to objects in the bank being
switched out will "at best cause unpredictable results."  The reason this
is so is the same as the reason that FPGDIR is dangerous.  If Tripod can
sell an item with functionality that's dangerous to use and assumes that
the user takes proper precautions, then I hope I can give away FPGDIR for
free with the same danger and assumptions.

What scares me, however, is the second moral.  People are hiding things
gleefully, without any idea that Memory Clear awaits them if they don't
know the pitfalls of PURGE on directories whose contents are all hidden.

EduCALC Goodies Disk #5 will, of course, have all this documented,
hopefully to make up for the blissful endorsement of using null-named
objects that has been on previous Goodies Disks.

Thanx, Bill, for warning us of the dangers here, before my "wonderful new
discovery" (*sigh*) proliferated too far.

-- a crestfallen jkh --