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From: gudeman@cs.arizona.edu (David Gudeman)
Newsgroups: comp.lang.misc
Subject: Re: "definition" rather than assignment (lazy evaluation)
Message-ID: <19196@megaron.cs.arizona.edu>
Date: 20 Mar 90 22:08:10 GMT
Organization: U of Arizona CS Dept, Tucson
Lines: 40

In article  <35045@ucbvax.BERKELEY.EDU> othar@ernie.Berkeley.EDU (Othar Hansson) writes:
>
>Is there any literature on taking assignment/initialization of
>variables as "definition", i.e., that
>
>mytype M = A*B;
>
>is taken to mean that M is defined as the product of A and B, and that
>changes to A will cause M to change?  Perhaps there's a
>general-purpose language in which this is done (aside from
>spreadsheets and special-purpose constraint languages)?

Doesn't Pascal allow this?  I don't recall the exact syntax, but it
seems that

  function M:mytype begin M := A * B end;

declares M as a function of no parameters (invoked without
parenthesis) that behaves like your M.  Of course, the defining sytax
isn't quite as nice.  For an interesting developement of the general
idea (not related to Pascal) see

%A Leslie Lamport
%A Fred B. Schneider
%T ``A Uniform Approach to Aliasing and Typing''
%J JACM
%P 205-216

(Hmm... Looks like I don't have the volume number or date.  Sorry.
Maybe someone else can give a better reference.)

Lamport & Schneider describe a fairly general mechanism (actually a
constraint programming language) used as the declaration section of a
programming language that is otherwise similar to the Ada/Pascal group
of languages.
-- 
					David Gudeman
Department of Computer Science
The University of Arizona        gudeman@cs.arizona.edu
Tucson, AZ 85721                 noao!arizona!gudeman