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From: dik@cwi.nl (Dik T. Winter)
Newsgroups: comp.lang.misc,comp.software-eng
Subject: Re: :=
Message-ID: <8442@boring.cwi.nl>
Date: 4 Oct 89 02:11:32 GMT
References: <1989Oct3.182931.518@jarvis.csri.toronto.edu>
Organization: CWI, Amsterdam
Lines: 48

In article <1989Oct3.182931.518@jarvis.csri.toronto.edu> malton@csri.toronto.edu (Andrew Malton) writes:
 > Apparently := to express the assignment operation was used faute de mieux
 > in Algol since the arrow <--- originally chosen for this purpose wasn't
 > available on teletypes. Does anyone know a reference for this story?
 > Or, is it folklore.
 > 
It is partly folklore.  (Oh dear, it appears that none of my Algol 60 reports
and Algol 60 revised reports are here at home, so the terminology may be a
bit wrong.)  Back in the time of Algol 60 transportation of a program by
means of paper tape (e.g. 5 level Alcor according to DIN standards) or
punched cards (Yuck) was no consideration (it simply was not done). So
there was a simple definition of the language where each installation
would provide the symbols to represent the language in some way.  There
was a publication language that contained all kind of symbols not found
on most punching devices of those times (like logical and and or, these
are still not found).  Also the publications used underscored words for
special words (so no reserverd words).  Btw. the device I used when
punching Algol 60 programs on 7-level papertape (a Friden Flexowriter)
knew about underlining and logical and, or and not etc, and of course
the compiler understood them also.

Difficult symbols were: string open/close, assignment, exponentiation,
lower 10 for exponents in numbers, multiplication (a serifless x),
logical and, or, not and equivalence, and of course underlined words.
(I may have forgotten some.)  And of course in Algol 60 case was (ought
to be?) significant.  The outlook of the report and revised report comes
mainly from the fact that it was produced by Peter Naur in Copenhagen
using said Flexowriter.  They lacked back arrows for assignment (they
were replaced by :=), proper string quotes (they were pasted by hand),
and exponentiation (I do not know what it looked like in the reports,
we used a vertical bar overprinting a logical and).
(I may be a bit wrong here, it is all from memory, and the Flexowriters
in Copenhagen were a bit different from those at our institute.)
I have seen Algol 60 programs with proper up arrows and left arrows
from other installations.  So it was not choosen as such in Algol 60
but by the users (the installations).

And of course I have seen programs like the following (using Knuths
much later Algol 60 notation from, I believe 1964):
	'debut'
		ecrit('('Allo monde.')')
	'fin'
We even had programs to translate French Algol 60 to English (to allow
us to compile and run programs from France) and vv. (to confuse our friends).
-- 
dik t. winter, cwi, amsterdam, nederland
INTERNET   : dik@cwi.nl
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