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From: steve@jplgodo.UUCP
Newsgroups: net.lang.f77
Subject: Re: possible implied-do bug?
Message-ID: <816@jplgodo.UUCP>
Date: Thu, 26-Jun-86 13:27:13 EDT
Article-I.D.: jplgodo.816
Posted: Thu Jun 26 13:27:13 1986
Date-Received: Sun, 29-Jun-86 05:33:08 EDT
References: <1452@alvin.mcnc.UUCP>
Organization: Jet Propulsion Labs, Pasadena, CA
Lines: 83
Keywords: implied do, parenthesis

In article <1452@alvin.mcnc.UUCP>, kenkel@mcnc.UUCP (Stephen Kenkel) writes:
> The following program compiles under VMS fortran, but not f77:
> 
> 	  dimension l(10),m(10),n(10)
>           write (*, * ) i,((l(k), m(k), n (k)), k=1,10)
> 	  end
> 
> This version works:
> 
> 	  dimension l(10),m(10),n(10)
>           write (*, * ) i,(l(k), m(k), n (k), k=1,10)
> 	  end
> 
> The extra parenthesis around the items in the implied do list
> appears to be causing trouble.  Is this a bug, or is the compiler
> in compliance with the standard?

It looks like f77 is complying with the standard and VMS Fortran has relaxed
the requirements.  Quoting from the ANSI standard:

	12.8.2.3 Implied-DO List.  An implied-DO list if of the form:

		( dlist, i = e1, e2 [,e3] )

	where: i, e1, e2, and e3 are as specified for the DO statement (11.10)

		dlist is an input/output list

	.......

	12.8.2 Input/Ouput List.  .....

	An input/output list is a list (2.10) of input/output list items and
	implied-DO lists (12.8.2.3).  An input/output list item is either an
	input list item or an output list item.

	.....

	12.8.2.2 Output list items.  An output list item must be one of the
	following:

		(1) A variable name
		(2) An array element name
		(3) A character substring name
		(4) An array name
		(5) Any other expression except a character expression
		involving concatenation of an operand whose length
		specification is an asterisk in parentheses unless the
		operand is the symbolic name of a constant.

	Note that a constant, an expression involving operators or function
	references, or an expression enclosed in parentheses may appear as
	an output list item but must not appear as an input list item.

	2.10 List

	A list is a nonempty sequence (2.1) of syntactic entities seperated
	by commas.  The entities in the list are called list items.


Essentially, the stuff after the ( in an implied-DO list before the indexing
information must be a valid I/O list.  The only time parentheses are allowed
in an I/O list is surrounding an expression or surrounding an implied-DO list.
A sequence of things seperated by commas is certainly not a valid Fortran
expression.  Since there is no loop index information given, it is not a
valid implied-DO list either.  Therefore it is not a valid I/O list item.

Editorial remark:
It has been my experience that VMS Fortran is *very* liberal in what it
will accept as valid Fortran.  If you care at all about being portable, get
a copy of the ANSI standard and throw away your vendor's manuals.  The other
recommendation I would make is to always use the /STANDARD qualifier when
you compile on a VAX.  This should flag most of the non-standard extensions
you are using.  I don't know how picky this is on a VAX since all of my
developement work is done on a Ridge but it should help.

-- 

...smeagol\			Steve Schlaifer
......wlbr->!jplgodo!steve	Advance Projects Group, Jet Propulsion Labs
....logico/			4800 Oak Grove Drive, M/S 156/204
				Pasadena, California, 91109
					+1 818 354 3171