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From: mark@cbosgd.UUCP (Mark Horton)
Newsgroups: net.college
Subject: Re: C.S. Dept. woes
Message-ID: <1278@cbosgd.UUCP>
Date: Tue, 17-Apr-84 20:08:13 EST
Article-I.D.: cbosgd.1278
Posted: Tue Apr 17 20:08:13 1984
Date-Received: Wed, 18-Apr-84 19:07:09 EST
References: <2540@csu-cs.UUCP> <3433@yale-comix.UUCP>
Organization: AT&T Bell Laboratories, Columbus
Lines: 38

Why do you want to draw a line?  There are disadvantages to practical
courses, and disadvantages to theoretical courses.  Nothing is perfect.
Are you proposing eliminating all courses more theoretical than X for
some X?

When I was an undergrad, one of the courses I hated most was Theory of
Computation.  It was hard (read impossible) for me to see how any of
these bizarre things like Post Productions and Finite State Machines could
possibly be useful in real life.  I only got a B in the course, and never
did understand the stuff in the second half very well.

The next semester, I took a "Compiler Construction" course.  One of my
favorite courses.  We started out with straightforward stuff: writing
a scanner, assembler, context free grammars.  But that problem of how
to parse seemed impossible.  Then LR parsing was introduced, and it used
something called a DPDA.  But a DPDA is just a Finite State Machine
with a stack!  Suddenly it hit me what good theory is - we get a lot of
really useful practical tools with a strong theoretical base.

When I did my thesis, I had to make certain functions table driven.  The
tables would be constructed separately for each programming language handled.
How did I know the tables could handle any unforseen programming language?
Well, the tables were a superset of pure Lisp, and pure Lisp is known to
be equivalent to a Turing machine, which in turn can do anything that
can be done in any computable function.  It was a lot easier to convince
my advisor that I could handle anything using this argument than "well,
see if you can come up with something I can't handle."

If you have 4.2BSD on your machine, you probably have sendmail.  Sendmail
is a nifty mailer whose flexibility, even on a binary only machine, is
nothing short of amazing.  How did Eric Allman embed this flexibility?
He used a variation on Post Productions as address rewriting rules.
If he hadn't taken a theory course, none of us would have sendmail today.

I'll admit, it sure would have been nice to have some of this motivation
when I was taking the course.

	Mark