Scala Stream call-by-need (lazy) vs call-by-name
Solution 1:
For example the Fibonacci series, implemented by adding the previous two elements to form the successor. Without memoization, that would have a linear slowdown (and stack growth) in the length of the sequence:
scala> lazy val fib: Stream[Int] = Stream.cons(0,
| Stream.cons(1, fib.zip(fib.tail).map(p => p._1 + p._2)))
fib: Stream[Int] = Stream(0, ?)
Example lazily (-sic-) copied from this blog