🚀 go-pugleaf

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In article <1995Dec6.000503.6676@sq.com> msb@sq.com (Mark Brader) writes:
<snip>
   To the question:

   > > > Is `i + (f(),i+i)' well defined? 

   Chris Volpe (volpe@ausable.crd.ge.com) writes:

   > It must yield one of two values, in an unspecified way, depending on which
   > of the two operands of the top-level "+" is evaluated first. (I've lost
   > some context here, but I assume f() modifies i.)  I wouldn't call this
   > "well-defined", but it does not invoke undefined behavior either.

   I agree with everything here and, I believe, in the rest of Chris's long
   article, *except* the implication that one of the two operands of the
   top-level + must be evaluated first.  I don't think Chris really meant to
   make that implication.  The evaluation sequence

	   f()
	   left-hand i
	   right-hand i
	   right-hand +
	   top-level +

   is one of the possibilities, and the left-hand operand of the top-level +
   is evaluated within the time that the right-hand operand is being done.

My question, which Chris was responding to, was whether the the i that
is the left operand of the top-level +, henceforth called the
top-level i, can be evaluated interleaved with the evaluation of f()
(Remember, f() contains a i=1). If it can, then there is a possible
sequence of evaluation where i is both modified (in f) and accessed
(top-level i) without intervening sequence points.

I do not have an opinion: how could I? As an ordinary user of the
language, all I can pray for is that the committee does not decide that
even this interleaving is prohibited by the panacea of `statements are
executed in sequence' :-( 

The issue of `f()+f()' is different: there one is talking of two
statements from two functions. Here we are talking about part of an
expression in the caller interleaving with evaluation of a statement
in f. In fact in `f()+f();', though the two operands of the + can be
interleaved, wasn't the informed opinion last time that _none_ of the
statements of one f can be evaluated before _any_ of the statements of
the other f, whatever effect that may have on optimization, though
which f is called first is indeterminate (Am I misremembering?). All
this to satisfy the _unsatisfiable_ edict of `statements are evaluated
in sequence': after all `f()+f();' is a statement --- is it done
before or after the statements comprising f? 

Cheers
Tanmoy
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