possible implied-do bug?
Stephen Kenkel
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?
Thanks.
Andrew Koenig
The compiler is in compliance with the standard.
The list of expressions in an implied DO must not be parenthesized.
Otherwise there would be an ambiguity:
write (*,*) ((3.0,4.0), k = 1, n)
Does this print ten alternating repetitions of 3.0 and 4.0,
or is (3.0,4.0) a complex constant?
Steve Dever
>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
>
The ANSI FORTRAN standard (section 12.8.2.3) states that an implied DO list
has the form:
(dlist, i = e1, e2 [, e3])
where dlist is an input/output list.
The standard does not allow an extra set of parentheses around
an I/O list in a READ or WRITE statement so the compiler is correct in not
accepting them. This was allowed in the FORTRAN-66 standard but was removed
to eliminate the syntactic conflict with complex constants in a list-directed
output list.
Steve Dever (sun!steved)
st...@jplgodo.uucp
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
Cathy
>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:
>
>
>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?
>
The compiler seems to agree with the standard. The syntax is:
io_implied_do_list
: "(" io_list "," id "=" exp "," exp [ "," exp ] ")"
;
io_list
: io_entity ( "," io_entity )*
;
io_entity
: array_variable
| io_implied_do_list
;
The extra bracket would imply an internal io_implied_do_list.
Best wishes,
Cathy
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