chain from @wlf

[Fairlight]

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.

mark->
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