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From: rpw3@fortune.UUCP
Newsgroups: net.lang
Subject: Re: Self-modifying code - (nf)
Message-ID: <2207@fortune.UUCP>
Date: Mon, 9-Jan-84 11:03:11 EST
Article-I.D.: fortune.2207
Posted: Mon Jan  9 11:03:11 1984
Date-Received: Tue, 10-Jan-84 05:45:16 EST
Sender: notes@fortune.UUCP
Organization: Fortune Systems, Redwood City, CA
Lines: 38

#R:fortune:-215700:fortune:15100006:000:1826
fortune!rpw3    Jan  9 02:49:00 1984

Another use of self-modifying code in TECO (the editor) was to solve
the conflict between speed and documentation. TECO did not have comments,
but it did have pretty nearly arbitrary tags as targets for goto's (anything
between exclamation points, like !This is a tag, including the spaces!).
So people who liked to use TECO's text-processing ability but were a bit
concerned about leaving cryptic hieroglyphs lying around (TECO has been
called the APL of editors) started using the practice of documenting
big TECO macros (programs) with otherwise unused tags (which can include
carriage returns, even):

	!begin!
		j	!make sure all is well by jumping to the top
	!	3d	!delete the leftovers from last pass
	!

and so on. Now the only problem with that is that TECO is a character-at-
a-time interpreter, and all those tags (comments) had to be parsed and
so the macro (program) ran SLOOOOOOWW! So before long every macro started
out with a little piece of code (editing commands) which saved what was in
the current buffer, got the macro, edited out all the tags with a <CR> in
them (leaving "real" tags), put the sped up macro in a q-register, restored
the buffer and jumped to the stripped version (whew!). In some cases it
meant a factor of 10 (!) in performance. Thus it was that whole subsystems
(mailing lists, label printers, order entry) came to be written and
maintained in TECO. Not only that, but since the clerical people used TECO
a little for their general WP jobs, they even started maintaining the macros
themselves. There even came to be a full-screen editor written in TECO!
(Was called either TED or KED, I forget.) Ah, the old days...

Rob Warnock

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