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Path: utzoo!utgpu!water!watmath!clyde!rutgers!labrea!decwrl!sun!steved
From: steved@sun.UUCP
Newsgroups: comp.lang.fortran
Subject: Re: "Interesting" error interpretation by f77.
Message-ID: <28327@sun.uucp>
Date: Thu, 17-Sep-87 15:00:06 EDT
Article-I.D.: sun.28327
Posted: Thu Sep 17 15:00:06 1987
Date-Received: Sat, 19-Sep-87 09:59:31 EDT
References: <5117@jade.BERKELEY.EDU>
Reply-To: steved@sun.UUCP (Steve Dever)
Organization: Sun Microsystems, Mountain View
Lines: 43
Keywords: FORTRAN parsing, error interpretation.

In article <5117@jade.BERKELEY.EDU> lagache@violet.berkeley.edu (Edouard Lagache) writes:
>
  [ A FORTRAN program containing the invalid lines:]
>      READ(*,*) NUM1, NUM2
>    SUM = NUM1 + NUM2
>
   [ Which produces the error messages]
>Error on line 4 of practice.f: syntax error
>Warning on line 9 of practice.f: local variable num2 never used
>Warning on line 9 of practice.f: local variable read never used
>                                                ^^^^
>----------------------------------------------> ???? <---------
>
>         After some discussion with the staff, we concluded that
>    the assignment was being interpreted before the I/O statement,
>    but that doesn't give me much satisfaction.
>
    ...
>
>                                                 Edouard Lagache
>                                                 School of Education
>                                                 U.C. Berkeley
>                                                 lagache@violet.berkeley.edu

The compiler's error message can best be uderstood by considering the
statement as seen by the compiler because of the illegal continuation
character.  It sees:

      READ(*,*) NUM1, NUM2M = NUM1 + NUM2

Since FORTRAN keywords are not reserved, the compiler must determine
from the context whether a particular sequence of characters is a
keyword or variable.  One way it does this is to scan the statement for
an '=' not enclosed within parentheses.  Since 'READ' is not a valid
keyword starting a statement with an '=', it takes the read to be
a variable.


-- 
---------------------------
Steve Dever          steved@Sun.COM
                          or
Sun Microsystems     sun!steved