Path: utzoo!attcan!uunet!lll-winken!lll-tis!helios.ee.lbl.gov!pasteur!ucbvax!ucsfcgl!seibel
From: seibel@cgl.ucsf.edu (George Seibel)
Newsgroups: comp.lang.fortran
Subject: Is DO WHILE difficult?
Message-ID: <11222@cgl.ucsf.EDU>
Date: 5 Nov 88 04:33:26 GMT
References: <75326@sun.uucp> <75328@sun.uucp> <604@quintus.UUCP> <2848@ima.ima.isc.com>
Sender: daemon@cgl.ucsf.edu
Reply-To: seibel@hegel.mmwb.ucsf.edu.UUCP (George Seibel)
Organization: UCSF Computer Graphics Lab
Lines: 29

In article <2848@ima.ima.isc.com> johnl@ima.UUCP (John R. Levine) writes:

>Actually, section 3.2.1 of the F77 standard says that "Comment lines may
>appear between the initial line and its first continuation line or between
>two continuation lines."  It also says that a line which is blank in the
>first 72 columns is a comment line, which is a minor pain for us compiler
>writers.

And in another article, ssd@sugar.uu.net (Scott Denham) writes:

>just wake up one morning and decide it would be nice to add say, a new 
>loop construct (DO WHILE ?) to their compiler.  These extensions cost the
>developers a signifigant amount of money.  [...]

    The common thread between these two articles is the reference
to apparently simple fortran extensions/features as being either
difficult or (equivalently) expensive to implement.   I'm not a
compiler writer, but for the life of me I can't see how some features
like blank line == comment, or  "!" == inline comment, or the
implementation of a DO WHILE are all that tough!   Wouldn't these
all be performed in a modern compiler's front end, i.e. the "easy" part?
    Am I just being naive about the complexity of these problems or
what? If some of you compiler writers out there would fill me in on
this, I'd appreciate it.
    And while you're at it, could anyone tell me if there are any
important compilers out there that actually insist on no more than
six character identifiers?   I'm thinking of allowing myself eight,
but I rather much like portable code.

George Seibel, UCSF