Functional programming

• Pure functions, no side effects like
  • reassigning a variable
  • modifying a data structure in place
  • Setting a field on an object
  • throwing an exception or halting with an error
  • printing to the console or reading user input
  • reading from or writing to a file
  • drawing on the screen eg: addition + on 2 integers is a pure function

Referential Transparency:

• An expression e is referential transparent if for all programs p, all occurneces of e in p can be replaced by the result of evaluating e, without affecting the observable behaviour of p.

Annotations:

• In java and scala Annotation are metadata that the compiler and runtime can use to infer how a method or class should behave.In a @tailrec annotation method, the Scala compiler will throw an error if our method was programmed to not be tail recursive, and thus make our code safer.

• throwing an exception breaks referential transparency. *