functional.md

goto is to structural programming assignment is to functional programming

Functions with no side-effects

• functions have to be pure - don't have side-effect
  1. does not change anything
  2. does not depend on anything that changes

Object orientation

• we can pass objects to function
• we can create objects within function
• we can return objects from function

Higher-Order function - functions are first class citizens

• we can pass function to function
• we can create function within function
• we can return function from function

What are the benefits?

Functional style vs Purely functional

• java - functional style
• haskel - Purely functional - doesn't allow mutability

What does it really mean to code in functional style?

• state transformation instead of state mutation
• method is a function which belongs to a class or to an object
• a function has 4 things
  1. name
  2. return type
  3. parameter list
  4. body
• lambda expression - constraint only two items from above
  • (parameter list) -> body
  • return type is inferred based on the context
  • name - who cares - anonymous
• Re-factoring from external to internal iterator
• internal iterator is polymorphic - applies on the collection/list passed
• type is inferred at compile time
• lambdas which receives the data and simply passes it -- office space pattern => change to method references

Fundamental shift: from imperative to functional style

Mapping operations - eliminating mutability

Declarative is expressive

• tell me what, not how

Imperative vs Declarative