In graduate school, perhaps 1989 or so, one of our bigger homeworks was to
implement a variable trap mechanism for assignments and for dereferences. I
believe the variable trap notion originated in one of the SNOBOL dialects, or
in SL5. From the 1989 class, there were about a dozen independent
implementations performed... on Icon version 7 or so. I do not know whether
any of them could ever be found. One thing that I remember is: it is harder
when you have to trap assignments to variables like L[i][j] or T[s] or r.x and
not just simple variables.
I know that I have wanted it pretty badly, though: variable traps are needed in
the udb debugger, to make a more efficient watch facility. Logically, it is
needed as part of the execution monitoring facilities.
So I propose a tweak to Bruce's question: *aside from debugging*, what uses can
you think of, for catching all assignments to a particular variable?
Cheers,
Clint
________________________________
From: Bruce & Breeanna Rennie <bren...@dcsi.net.au>
Sent: Sunday, January 22, 2017 1:44:46 PM
To: Unicon group
Subject: [Unicon-group] Trapped variable processing and extending this facility
to other user defined variables
Greetings to all,
Thanks to Clinton and Don Ward, we now have the new Unicon/Icon
Implementation Book available within the sourceforge download.
As I have been away from internet access, I have been reading the
current book as a evening activity. The section on trapped variables has
given rise to a question as follows.
Is there a use for or a need for this ability to associate a function
that can run when a value is assigned to a specific variable?
For example, in Unicon, one is allowed to define a default type and
value for procedure parameters. Is this a valid situation in which any
such variables could be created as trapped variable using a new system
defined function to make this a user define d trapped variable?
Are there other situations where such a facility could be useful?
regards
Bruce Rennie
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