Functional Programming

Jul 28, 2023

• OOP

• OCaml
• Scheme
• Rust
• C++
• ReactJS

Programming in a functional style often includes using functions as values by passing them in arguments, returning them from other functions, assigning them to variables for later execution, and so forth.
Adapting to that perspective requires letting go of old ideas: assignment statements, loops, classes and objects, among others. That won’t be easy.

A function maps an input to an output; for the same input, it always produces the same output. That is, mathematical functions are stateless: they do not maintain any extra information or state that persists between usages of the function.
Functions are first-class: you can use them as input to other functions, and produce functions as output. Expressing everything in terms of functions enables a uniform and simple programming model that is easier to reason about than the procedures and methods found in other families of languages.

• No mutable data (no side effect).
• No state (no implicit, hidden state).
• All state is bad? No, the hidden, implicit state is bad.
• Functional programming does not eliminate state, it just makes it visible and explicit (at least when programmers want it to be).
• Functions are pure functions in the mathematical sense: their output depend only on their inputs, there is no “environment”.
• The same result returned by functions called with the same inputs.

• Pattern Matching
• Closures, a function-like construct you can store in a variable
• Iterators, a way of processing a series of elements

let rec fast_fib n =
  let rec helper i pp p = 
    if i = 0 then pp
    else helper (i - 1) (pp + p) p
  in
  if n = 0 then 0 
  else helper n 0 1

• Rust Functional Programming
• Higher Order
• Monad