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From: grover@brahmand.Sun.COM (Vinod Grover)
Newsgroups: comp.lang.misc
Subject: Re: What is Lazy Evaluation?
Keywords: expression evaluation, lazy evaluation
Message-ID: <131929@sun.Eng.Sun.COM>
Date: 16 Feb 90 02:50:02 GMT
References: <3109@caesar.cs.montana.edu> <6081@bd.sei.cmu.edu>
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Reply-To: grover@sun.UUCP (Vinod Grover)
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In article <6081@bd.sei.cmu.edu> firth@sei.cmu.edu (Robert Firth) writes:
>
>Example:
>
>	munge(1/x)
>
>greedy evaluation will evaluate 1/x and then call munge().  lazy
>evaluation will call munge(), and evaluate 1/x only when the body
>of munge referenced its formal parameter.
>
>As the example shows, lazy evaluation "works" in cases where greedy
>evaluation does not - in this case, if x=0 but munge doesn't reference
>its parameter.

Lazy Evaluation differs fromn call-by-name in that the expression is
evaluated at-most-once. If there are multiple refrences to 1/x, in the above
example, only one of them will be evaluated if needed.