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From: rcosw@koel.co.rmit.oz (Simon Wail)
Newsgroups: comp.lang.pascal
Subject: Pascal Assignment statements
Message-ID: <723@chudich.co.rmit.oz>
Date: 5 Oct 89 03:23:10 GMT
Sender: news@chudich.co.rmit.oz
Lines: 38

I have a question about expression evaluation in assignment statements in
Standard Pascal.

Q. Is all address calculations of the assignment variable performed before
   the expression on the R.H.S. is evaluated???

Some examples that cause problems :

x[a+b] := f;

	where "f" is a function that modifies the global variables "a" and "b"
	which are used to index the array on the L.H.S.  Is the index to the
	array calculated before "f" is called???

x[5].ptr^.y := f;

	where "f" is a function that modifies the fifth element of the 
	array "x" so "ptr" points to a different record.  Is the old value
	of "ptr" used to modify "y" or the new value of "ptr" changed 
	in "f"????

I know these are examples of terrible side-effects and bad programming style,
but when one is writing a Pascal compiler it is necessary to take into account
all the possibilities and to be consistent when evaluating expressions.

Thanks.
-------------------------------------------------------------------------------
Simon Wail,
Post Graduate Student.

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RMIT / CSIRO Parallel Systems Architecture Project,
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Royal Melbourne Institute of Technology,
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