Path: utzoo!mnetor!uunet!husc6!sri-unix!quintus!ok
From: ok@quintus.UUCP (Richard A. O'Keefe)
Newsgroups: comp.lang.misc
Subject: Re: History of := (was: == vs =)
Message-ID: <576@cresswell.quintus.UUCP>
Date: 25 Jan 88 05:06:20 GMT
References: <2337@haddock.ISC.COM> <51300003@uxe.cso.uiuc.edu> <20123@bbn.COM>
Organization: Quintus Computer Systems, Mountain View, CA
Lines: 20
Summary: Eh?

In article <20123@bbn.COM>, cosell@cosell.bbn.com (Bernie Cosell) writes:
> Well, the first time _I_ saw := was in Algol.  It is all real hazy now,
> but as I recall, Algol had _three_ variants of '=':
>    =    boolean -- tested if a equalled b 
>    :=   assignment -- evaluated b and assigned that value to a.
>    ::=  definition -- a was defined to be 'b' as a macro.
Algol 60 hasn't got macros.  Algol 60.1 hasn't got macros.  Algol 68
hasn't got macros.  Burroughs Extended Algol has macros, but you do
	define foo(a,x) = replacement;
It isn't hard to find out about Algol 60.  Why not check the facts
before spouting?

:= has been used in mathematics for a long time to mean "is defined as".
For example:
	interior(S):= complement(closure(complement(S)))
Another convention is = with "def" subscripted, e.g.
	o       __
	S =    (S')'
	   def
----