Re: constant folding at parse time

wjw@eb.ele.tue.nl (Willem Jan Withagen) writes:
      Now I don't want to open another tarpit again, but this certainly is going
      to have effects on the semantics of the used program.


Yes, indeed. That's why you need an exacting specification of what the
language permits and forbids (as far as the visible consequences of
expression rearrangements go), and a thorough knowledge of the properties
of the arithmetic of the target computer.


Sadly, most language specifications don't discuss these issues, or discuss
them in such vague terms that it is very difficult to resolve ambiguous
cases.


I suppose that a really good compiler-generating system would be
parameterizable for all these matters, but I've never heard of such a
thing.


Dale Worley Dept. of Math., MIT drw@math.mit.edu
[Are there specification languages that would allow you do define your
language precisely enough to tell you mechanically whether a proposed
optimization was valid? -John]
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