Path: utzoo!attcan!uunet!lll-winken!lll-tis!helios.ee.lbl.gov!pasteur!ucbvax!decwrl!hplabs!hpda!hpcuhb!hpcllla!hpclisp!hpclcdb!cdb
From: cdb@hpclcdb.HP.COM (Carl Burch)
Newsgroups: comp.lang.fortran
Subject: Re: fortran problem
Message-ID: <6690017@hpclcdb.HP.COM>
Date: 13 Jun 88 19:59:13 GMT
References: <8806111222.AA06982@jade.berkeley.edu>
Organization: HP ITG/ISO Computer Language Lab
Lines: 32



Unfortunately, any such program is not standard-conforming, and the standard
therefore says exactly nothing about its required behavior.  The relevant
passage of the F77 standard is paragraph 15.9.2 on page 15-16 :

     "Actual arguments may be constants ... if and only if the associated
      dummy argument is a variable that is not defined during execution of
      the referenced external procedure."

The Fortran 8x draft standard has similar words, and is quite likely to
retain them in light of the F8x Prime Directive - to be 100% F77 compatible.

There are some tools that try to find such problems - see the previous
notestrings on Fortran lint.  I don't know if they mentioned MAT from SAIC,
or flint from Programming Research Ltd in England.  I haven't used either
one, but they're both made by nice guys that know more about the problem
than I do.

As for your general implication on the quality of compilers that cause
this sort of problem, I wish you hadn't mentioned the specific companies
you compared - I could be somewhat more candid in the abstract.  As it is,
I will just report that the problem you cite was used as a horror story
in the compiler-writing class I took at Purdue in 1981 - with the professor's
opinion that this story is so famous that nobody would ever do it "wrong"
again.  Silly him.  Actually, after a similar conversation with a couple HP
customers at a users group conference I found to my dismay that HP still
has one compiler (F7x on the HP1000) that also allows constants to change
value this way.  So (as the saying goes) "Let's be CAREFUL out there!"

						- Carl Burch
						  cdb%hpda@hplabs.HP.COM
						  HP Fortran Team