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From: Pat.Terry@p101.f19.n490.z2.fidonet.org (Pat Terry)
Newsgroups: comp.lang.modula2
Subject: Termination
Message-ID: <945.243C1EDF@dawggon.fidonet.org>
Date: 7 Apr 89 04:33:29 GMT
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In article <6380@medusa.cs.purdue.edu>
rjh@cs.purdue.EDU (Bob Hathaway) writes

>Ok, I saw termination code at module scope exit as a generalization of this
>idea, with program termination code being specified as termination code for
>the main program module.

One way of looking at it, certainly "self consistent".

>>I take this to mean you would also like to be able to write, for example
>>
>>      PROCEDURE x;
>>        (*inner*) MODULE y;
>>         . . .
>>        BEGIN
>>          Initialise;
>>          SetTerminate(Cleanup)
>>        END y;
>>
>>        ...
>>      END x;
>>
>>so that whenever x was called "Initialise" was invoked, and whenever x
>>returned "CleanUp" was invoked.

>Yes, this is what I meant.  However, for top-level modules serving as
>abstract state machines there is no means for calling CleanUp just before
>the end of x, since no x exists, and an explicit termination code section
>is therefore required.

No, but x has to be "called", and so its "body" can call CleanUp each time
this call is made, just before it "returns"?

>As I remember, Pascal-Plus has something like the following syntax:

Something like, certainly.  But in Pascal Plus the "envelopes" are much
more like "classes", and act as "templates" of which one then creates
instances, as many as one likes/needs.  The Modula-2 MODULE can't be
replicated in quite the same nice way (which I take to be what you would
really need for abstract state machines)  The SetTermination proposal is in
line with lots of M-2 - find a simple way of handling 90% of the cases with
10% of the effort needed for a larger language (and does not require a
syntactic addition to the language as the Pascal-Plus *** statement would
be).


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