08-streams-and-lazy-evaluation.md

Streams and Lazy Evaluation

Streams

• A stream is a list whose tail is evaluated only on demand.
  • can be infinite or finite (don't care)

List vs Streams

• Are basically same in structure
• Differences :

type 'a list = Nil | Cons of 'a * 'a list
type 'a stream = Nil | Cons of 'a * (unit -> 'a stream)

Computation is delayed by introducing a closure

Lazy initialization in Scala

lazy val x = expr

Like call-by-need.
It is powerful in scala because it is thread-safe.

Lazy initialization in Java

• How many lines of Java code you need to implement lazy eval in Java? => 10+ lines
  • Needs double-locking design pattern + volatile class => Because Test-and-set in JAVA is not atomic.
• Concurrent programming requires deep understanding of memory model of that language.

Infinite Streams