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From: mjs@hubcap.clemson.edu (m j saltzman)
Newsgroups: comp.lang.fortran
Subject: Re: Duplicate names in formal parameter lists
Message-ID: <11101@hubcap.clemson.edu>
Date: 23 Oct 90 15:02:45 GMT
Distribution: usa
Organization: Clemson University
Lines: 65
References:<11084@hubcap.clemson.edu# <2385@cod.NOSC.MIL><KHB.90Oct22115411@chiba.Eng.Sun.COM>
Followup-To:
Keywords:

In article <KHB.90Oct22115411@chiba.Eng.Sun.COM% khb@chiba.Eng.Sun.COM (Keith Bierman fpgroup) writes:
%In article <2385@cod.NOSC.MIL% burkley@cod.NOSC.MIL (V. J. Burkley) writes:
%
%   In article <11084@hubcap.clemson.edu% mjs@hubcap.clemson.edu (m j saltzman) writes:
%...
%    What happend?  An intermittent error that was harder than hell to find.  I 
%    don't know why compilers don't check for it, it 
%...
%
%The primary function of compilers is to generate executable code.
%There are tools which do full static checking of programs (across
%subroutine boundries), SOME such tools are:
%[list of products deleted]
%
%Note that
%
%		call foo(x,x)
%
%is legal (conformant with ANSI X3.9-1978) or not, depending on code
%inside of subroutine foo. In order to allow standard conforming codes,
%one mustn't disallow the call without examining the callee.
%

Sure, I understand that.  My complaint was that the SUBROUTINE statement
with two identical _formal_ parameters wasn't caught.  This doesn't
require global static checking to recognize--it's just like a duplicate
declaration.  (Interestingly, DOUBLE PRECISION X,X doesn't generate an
error either--although declaring the same variable with different types
does.  Now duplicate declaration of a variable with the same type is a
benign error, but the duplicate parameter is not.)

I don't think the question of whether SUBROUTINE FOO(X,X) can be
conformant under any circumstances has been resolved yet.  Although
there are numerous ways to assign a sensible semantics to CALL
FOO(X,X) (even if X is modified by FOO), I don't think there are any
for SUBROUTINE FOO(X,X) (unless maybe X is write-only and calling is
by value/return?).

%--
%----------------------------------------------------------------
%Keith H. Bierman    kbierman@Eng.Sun.COM | khb@chiba.Eng.Sun.COM
%SMI 2550 Garcia 12-33			 | (415 336 2648)   
%    Mountain View, CA 94043

And in article <107528@convex.convex.com% patrick@convex.COM (Patrick F. McGehearty) writes:
%In article <11084@hubcap.clemson.edu% mjs@hubcap.clemson.edu (m j saltzman) writes:
%>
%>	SUBROUTINE FOO(X, [other parameters], X)
%>	...
%>This compiled without error on a Sun (with the -u flag) and on ULTRICS.
%...Could it be that both of these compilers derive from the original Berkeley
%...Unix f77 compiler?
%The likely behavior on those compilers which ignore the error is to choose
%one argument (probably the later one) and use it throughout the subroutine.
%In any case, this looks like a clear programming error to me.
%A Convex compiler gives an error complaining X being declared twice and
%about the dummy argument appearing twice.

Yes, it was a programming error, and yes, the Sun compiler does
exactly what you describe.

Thanks to everyone who responded here, and by e-mail.

		Matthew Saltzman
		mjs@clemson.edu