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From: jlg@cochiti.lanl.gov (Jim Giles)
Newsgroups: comp.lang.fortran
Subject: Re: Questions about IF
Message-ID: <26462@beta.gov>
Date: 25 Jun 91 20:10:38 GMT
References: <scNB_TG00WBMQ0ykwM@andrew.cmu.edu> <1991Jun24.213601.11329@milton.u.washington.edu> <26384@lanl.gov> <1991Jun25.124806.15349@cs.dal.ca>
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Organization: Los Alamos National Laboratory
Lines: 23

In article <1991Jun25.124806.15349@cs.dal.ca>, silvert@cs.dal.ca (Bill Silvert) writes:
|> In article <26384@lanl.gov> jlg@cochiti.lanl.gov (Jim Giles) writes:
|> >Actually, the standard does require that no optimization 
|> >violate parenthesis.  So you can force the order of
|> >evaluation any way you want:
|> >
|> >      If (expr1 .and. (expr2.and.expr3)) then
|> >         ...
|> >
|> >This does the second '.and.' first.  The other question was about
|> >short-circuiting: the standard _allows_ short-circuiting but does
|> >not _require_ it.
|> 
|> Sorry, this doesn't make sense to me.  All the parentheses guarantee is
|> that expr1 will not be evaluated second.  Both the sequences 1-2-3 and
|> 3-2-1 are consistent with the given parentheses.

You misunderstand the parenthesis rule.  The objects I've called
`expr1', `expr2', and `expr3' can be evaluated in _any_ order.
The parenthesis force the 'and' between `expr2' and `expr3' to 
be evaluated before the other 'and'.  That's all.

J. Giles