chain from @wlf

[GCC Consulting]

> -----Original Message-----
> From: filepro-list-bounces at lists.celestial.com 
> [mailto:filepro-list-bounces at lists.celestial.com] On Behalf 
> Of Joe Chasan
> Sent: Friday, April 15, 2005 3:29 PM
> To: Fairlight
> Cc: filePro Mailing List
> Subject: Re: chain from @wlf
> 
> On Fri, Apr 15, 2005 at 02:49:53PM -0400, Fairlight wrote:
> > The honourable and venerable Joe Chasan spoke thus:
> > > fp 5.0.14, unix.
> > > 
> > > Is anyone using chain command successfully from @wlf while within 
> > > update on a record within *clerk?
> > > 
> > > I have a table that works by itself, works when chain'ed 
> from @key, 
> > > yet if i chain to it from within update on a record from @wlf, 
> > > within the chain'ed to table clerk is completely confused 
> as to what 
> > > line #'s it should be executing, going to lines that are never 
> > > referenced, executing partial subroutines, or giving SegV's.
> > > 
> > > I had though this was working for a while, I don't see in docs 
> > > anywhere that says can't chain from within update...
> > 
> > Disclaimer:  I have not seen the fP source code, and these are 
> > educated guesses.
> > 
> > That said, it seems like a fairly safe assumption from a 
> logical point 
> > of view that you're confusing the table handler by -where- you're 
> > triggering it.
> > 
> > I was under the impression that chain was used primarily in 
> the early 
> > days to get around table length limitations.  I've been 
> told that it 
> > basically
> > -replaces- the table that made the chain call with the 
> target of said call.
> > 
> > If you have event triggers like @key, @wlf's, @wef's, etc., and you
> > -replace- the table in memory, you were at a place in memory while 
> > executing those, and those places just got overwritten--or 
> at the very 
> > least the pointers are no longer to the correct locations 
> for various 
> > events.  So any WHEN processing events you had coded should, from a 
> > logical point of view, completely vanish and become null and void.  
> > I'd say it might make sense if it was programmed to pick up on new 
> > WHEN processing in the new table, but I somehow don't think they 
> > anticipated someone chaining out of an event and nuking all 
> their triggers in event-handler.
> > 
> > Best guess, but I think you're probably corrupting memory 
> by using it 
> > for something it was probably never intended for.
> > 
> > It'll be interesting to see Ken's answer, though.
> 
> so would i.
> 
> as a consultant who lots of time has to work with 
> programs/tables/etc written by other people, sometimes its 
> advantageous to work in a "clean"
> environment that call/chain offer - when you have a 1500 line 
> table with
> 15 screens and 80% of the 2 letter dummies already used, it 
> is certainly a lot less work to be able to modularize what 
> can essentially be a stand-alone program in its addition than 
> to retrofit it into such a limited environment.  
> 
> Call is too limited in fact that many tools one likes to use 
> for interactive @wlf processing commands don't work, can't 
> nest calls, etc, so once in a while I like to play with chain 
> for this.
> 
> it is easy enough to set long dummies to whatever 
> tables/screen/fields you were in before/after chain so that 
> you can transparently go back exactly where you started from.
> 
> --- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 
> - - - ---
> -Joe Chasan-                      Magnatech Business Systems, Inc.

Joe,

Years ago I used chain for a cash receipts program which handled commissions
which could either be paid by the seller or the buyer on the transaction.

When the program started, a listbox appeared and the clerk selected either a
seller or buyer paid check. Since most payments were from sellers, only when
buyer was selected did the program chain the buyer version.  When completed, I
chained back.  I set a dummy variable in auto which was tested upon return,  if
set, the program went to the closing routine for the check.

Granted, this is not from @wlfxx processing.

I would assume the some programmers may be using chain alone with @menu in clerk
to execute the proper programming based on the selection being made.

Richard Kreiss
GCC Consulting