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From: rpw3@fortune.UUCP
Newsgroups: net.lang
Subject: Re: loop indexing - (nf)
Message-ID: <2283@fortune.UUCP>
Date: Mon, 16-Jan-84 04:02:57 EST
Article-I.D.: fortune.2283
Posted: Mon Jan 16 04:02:57 1984
Date-Received: Tue, 17-Jan-84 02:41:32 EST
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Organization: Fortune Systems, Redwood City, CA
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#R:uvacs:-112200:fortune:15100008:000:851
fortune!rpw3    Jan 15 20:24:00 1984

In some languages, you can say things like

	for all x in {set/range/list} do ...;

so to add all the values of a singly-dimensioned array

	s := 0;
	for all i in { lowbound(a):highbound(a) } do s := s + a[i];

Notice that the compiler can use random order, if it likes, as long
as it covers all of the entries.  These things are in the class of
language features called "generators". Generators were introduced
exactly to address the point of the previous note: We sometimes need
ways to indicate to the compiler a set of computations to be done,
without implying an ordering to that set.

(I'm afraid I've forgotten what languages use generators, other than
SCHEME's "streams".)

Rob Warnock

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