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From: campbell@maynard.BSW.COM (Larry Campbell)
Newsgroups: comp.os.vms
Subject: Re: marketing vs. demerit
Message-ID: <2822@bsu-cs.UUCP>
Date: 1 May 88 02:23:39 GMT
Sender: dhesi@bsu-cs.UUCP
Lines: 41

In article <2725@bsu-cs.UUCP> dhesi@bsu-cs.UUCP (Rahul Dhesi) writes:
<>Based on a superficial (and rather skeptical, raised-eyebrow) look
             ^^^^^^^^^^^
<>at VMS, I conclude as follows.
<>
<>VMS's design makes it very difficult to include structured control
<>structures in DCL.  The UNIX shells can save their context between
<>commands because they execute other programs as subprocesses.  Under
<>VMS subprocess creation is so painfully slow that it is seldom done.
<>Thus the DCL interpreter cannot save its entire context when executing
<>another program.  To use while loops and if-then statements the DCL
<>interpreter would have to save quite a bit of the current context so it
<>could continue executing the current control structure.  Nested control
<>structures would require even more information to be saved.  Alas, the
<>DCL interpreter and VMS make this nearly impossible.
<>
<>This is also the reason why VMS does not allow multiple commands
<>on the same line.  Doing so would mean saving the command line
<>between executions of different programs so the command interpreter
<>could then pick the next command on the same line.

[This is really getting off the comp.lang.c track, so I've cross-posted
and directed followups to comp.os.misc]

A little knowledge is a dangerous thing, Rahul.  Although VMS does not
create new subprocesses to run user programs, DCL does not have to get
out of the way when running a user program because the address space
is divided into two parts -- one for the user and one for DCL (and RMS).
The user part keeps getting zapped and reloaded with user programs,
but the DCL/RMS part (P1 in VMS jargon) stays around as long as you're
logged in.

So there is no _technical_ reason why DCL couldn't easily have multiple
commands per line, and reasonable control structures.  The reason it
doesn't is cultural -- the VMS people have a FORTRAN mentality.  For a
FORTRAN-inspired system, VMS isn't too bad.  ("Gee, for a fat girl,
you don't sweat too much.")
-- 
Larry Campbell                                The Boston Software Works, Inc.
Internet: campbell@maynard.bsw.com          120 Fulton Street, Boston MA 02109
uucp: {husc6,mirror,think}!maynard!campbell         +1 617 367 6846