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From: djones@megatest.UUCP (Dave Jones)
Newsgroups: comp.lang.misc
Subject: Re: Lazy Evaluation... a simple example
Message-ID: <12037@goofy.megatest.UUCP>
Date: 16 Feb 90 00:31:38 GMT
References: <7476@mentor.cc.purdue.edu>
Organization: Megatest Corporation, San Jose, Ca
Lines: 17

From article <7476@mentor.cc.purdue.edu>, by ksb@mentor.cc.purdue.edu (Kevin Braunsdorf):

...
> 
> What I did was much simpler than most of the systems I saw described at
> the time.  I simply made `cons' defer evaluation of its arguments until
> either `car' or `cdr' was called on the resulting CONSBOX (which was
> tagged as being LAZY, and had a saved environment hung on it).

Just for the record, what you did is not full lazy evaluation. But
as I noted earlier, defering the evaluation of a CONS is probably
the most important 'lazy deferal' for practical purposes.

There's a book that explains an implementation of lazy evaluation
pretty well, called _Functional Programming, Application and Implementation_,
by Peter Henderson, Prentice-Hall 1980. I don't know if it's still in
print or not.