code in scala   def unfold[A, S](z: S)(f: S => Option[(A, S)]): LazyList[A] = f(z) match { case Some((h, s)) => h #:: unfold(s)(f) case None => LazyList() }

Database System Concepts
7th Edition
ISBN:9780078022159
Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Chapter1: Introduction
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code in scala

 

def unfold[A, S](z: S)(f: S => Option[(A, S)]): LazyList[A] = f(z) match { case Some((h, s)) => h #:: unfold(s)(f) case None => LazyList() }

 

A positive integer is perfect if it equals the sum of all of its factors, excluding the number itself. For example, 6, 28, 496, and so on. Define a LazyList to generate an infinite list of perfect numbers.  Use higher-order functions whenever possible.  [Hint: One way to do this is by (1) having one function construct a list of factors (use unfold and filter for this), (2) having another function which folds the list of factors into their sum, and (3) creating a LazyList using unfold, filter and the previously constructed functions.] 

e number itself. For example, 6, 28, 496, and so on. Define a LazyList to generate an infinite list of perfect

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