functional programming is a way of writing code by means of pure functions

benefits of functional programming:

1. Immutability

   • All values derived from old values

2. Testability

   • Pure functions are easy to test

difficulties of functional programming:

1. unintuivive

   • many people learn programming either imperatively or in an object-oriented manner

2. impractical?

   • interfacing with "the real world" is challenging