Functional Programming

• Functional programming is a style of building the structure and elements of computer programs — that treats computation as the evaluation of mathematical functions and avoids changing-state and mutable data .

• pure functions is :
  • It returns the same result if given the same arguments (it is also referred as deterministic).
  • It does not cause any observable side effects.

• If our function reads external files, it’s not a pure function .

• Pure functions are stable, consistent, and predictable.

• Pure functions benefits is that the code’s definitely easier to test.

• Functions as first-class entities can:
  • refer to it from constants and variables.
  • pass it as a parameter to other functions.
  • return it as result from other functions.
• Higher-order functions:
  • When we talk about higher-order functions, we mean a function that either:
    • takes one or more functions as arguments, or
    • returns a function as its result
• The doubleOperator function we implemented above is a higher-order function because it takes an operator function as an argument and uses it.
• Map : The idea of map is to transform a collection.

• The map method transforms a collection by applying a function to all of its elements and building a new collection from the returned values.

• Filter: Given a collection, we want to filter by an attribute.
• The filter function expects a true or false value to determine if the element should or should not be included in the result collection.

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