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From: paulg@bhpmrl.oz.au (Paul Gallagher)
Newsgroups: comp.databases
Subject: Re: dbase IV "popup" while editing data with "read" command
Keywords: dbase, data entry
Message-ID: <1991Apr17.110913.7460@bhpmrl.oz.au>
Date: 17 Apr 91 11:09:13 GMT
References: <881@imec.UUCP> <1991Apr5.164724.4798@dbase.A-T.COM> <1991Apr5.165347.4981@dbase.A-T.COM>
Sender: usenet@bhpmrl.oz.au (USEnet nntp account)
Organization: BHP Research - Melbourne Laboratories, AUSTRALIA
Lines: 73


I want to mention a few BUTs, IFs and F***s regarding this admittadly
brilliant capability of dBase IV.

I'm currently working on a couple of projects that implement nested
READs via VALIDation UDFs - the general scenario is:

   - read GETs     
   - use VALID clause to call UDF which:
        - checks user input match with "lookup" database
        - if exact match, fill in mvar 
        - if partial match, activate picklist (as described in prior messages)
        - if no match, ask user whether picklist or new entry
        - if new entry, activate new window and appropriate @...

I've nested this procedure up to three times, but in doing so, I had to
overcome some of the most frustrating, depressing, infuriating (etc)
problems I've ever seen.

Here's how it went: some time ago I implemented this procedure with
one level of nesting and thought "Wow, this is great!". Two weeks ago
I did my first implementation with two levels of nesting - you know,
cut-and-paste code etc. Disturbingly, on return from either of the
VALIDation UDFs up popped an "Unknown command code" error message
(not trapped by the debugger of course - are A-T living in this century
do you think?) After hours of code reconstruction, line-by-line - a process
which is not exactly fast especially since I am only using a 10MHz XT -
I found that by selectively commenting out MESSAGE clauses to the 
@..SAY..GETS involved I could at a whim generate any one of the
following error messages on return from the UDFs : "Unknown command code",
"Not a character expression" and "Not a numeric expression".
By removing all MESSAGE clauses, I could dispense with the errors
completely.

So, (allbeit without MESSAGES) I finally had the thing running. I've yet
to speak to A-T about this, but my best guess is that dBase IV (V1.1 btw)
was either having stack problems or perhaps not managing a lack of 
memory properly, or even not managing it's own internal memory allocation
properly. All I can say is that our local A-T help line is damned lucky
it doen't operate at 2am else they would have had one hell of an earbashing!

Now I've tempted fate (what are users for?) and tried nesting three levels
deep. The error message is different again of course (who ever heard of
systemmatic bugs!?!). Now the UDFs return .F. even though the returned
variable is _DEFINITELY_ .T. - even the "debugger" says so! BUT, this error
is not a cert. - sometimes the procedure works when following the same
steps from scratch. I've yet to resolve this problem.

On the bright side, I've probably got some of the most consistent, well
documented, standards-based code now after working through it umpteen times
to make sure the bugs weren't my fault.

PS: I've recently returned to dBase programming after a 12 month hiatus.
I remember back then, after grappling with the dBase IV V1.0 bug 
involving array assignation using macro substitution (which chewed up
memory like nothing else - and never spat it out), that I swore I'd
never touch dBase again, but if I did _always_ assume the bug's in dbase,
not your code(!), lest you wish to waste hour after frustrating hour.
Nothing dulls the memory like time of course.

Thanks for the shoulder to cry on. I'd like to hear other's experiences
along these lines though. Is this a problem someone else out there has
had?

Paul Gallagher

     /\/\       Paul Gallagher, PC Support Officer,
    / / /\      Computer Systems Group,
   / / /  \     BHP Melbourne Research Laboratories
  / / / /\ \    245 Wellington Rd Mulgrave Vic 3170 AUSTRALIA
  \ \/ / / /    Phone : +61-3-560-7066,  Fax : +61-3-561-6709
   \  / / /     ACSnet  :  paulg@bhpmrl.OZ.AU        
    \/\/\/