Why Functional Programming?

@volpegabriel87

@gvolpe

Paradox of programming

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@volpegabriel87

  • Local perspective
  • Progress oriented
  • Detail
  • Vast memory
  • Pretty reliable
  • Machine language

Machine / Human impedance mismatch

@gvolpe

"A crash course in Category Theory" by Bartosz Milewski (2017)

  • Global perspective
  • Goal oriented
  • Idea
  • Limited memory
  • Error prone
  • Mathematics

λ-calculus

@volpegabriel87

@gvolpe

"A set of postulates for the foundation of logic" by Alonzo Church (1932)

 

A universal model of computation that can be used to simulate any Turing Machine

 

A formal system for expressing a computation based on function abstraction and application

LISP

@volpegabriel87

@gvolpe

"LISP specification" by John McCarthy (1958)

 

Originally created as a practical mathematical notation for computer programs, influenced by the Lambda Calculus system

 

He also invented garbage collection (implemented in LISP)

Erlang

@volpegabriel87

@gvolpe

Developed by Ericsson ( Joe Armstrong, Robert Virding, and Mike Williams) in 1986

 

Distributed, fault-tolerant and highly available

 

Open Telecom Platform (OTP)

@volpegabriel87

@gvolpe

Haskell committee at FPCA (1987)

 

Haskell 1.0 (1990)

 

First versions didn't support I/O

 

"Escape from the ivory tower: the Haskell journey" by Simon P. Jones

Functional Programming

Functional Programming

@volpegabriel87

@gvolpe

"Why functional programming matters" by John Hughes (1990)

 

- Higher-order functions

- Lazy evaluation

 

Leads to better modularity

Functional Programming

@volpegabriel87

@gvolpe

"Comprehending Monads" by Philip Wadler (1990)

 

- Maybe Monad

- List Monad

 

Sequential computations

Functional Programming

@volpegabriel87

@gvolpe

Monads

foo :: Maybe Int
foo = Just 1

bar :: Maybe Int
bar = Just 2

sum :: Maybe Int
sum = foo >>= \x -> bar >>= \y -> return (x + y)

sum' :: Maybe Int
sum' = do
  x <- foo
  y <- bar
  return (x + y)

Functional Programming

@volpegabriel87

@gvolpe

"Imperative functional programming" by Simon P. Jones and Philip Wadler (1992)

 

- IO Monad

- Connecting I/O operations

 

Ability to mix imperative and purely functional programming, without ruining either

Functional Programming

@volpegabriel87

@gvolpe

IO Monad

toUpper :: Char -> Char
getChar :: IO Char
putChar :: Char -> IO ()
(>>=) :: IO a -> (a -> IO b) -> IO b
return :: a -> IO a
getChar >>= (\a -> putChar a)

@volpegabriel87

@gvolpe

Haskell & PureScript & Scala

Console program

main :: IO ()
main = do
  putStrLn "Enter your name:"
  n <- readLn
  putStrLn ("Welcome " <> n)
val program: IO[Unit] =
  for {
    _ <- IO(println("Enter your name:"))
    n <- IO(StdIn.readLine)
    _ <- IO(println(s"Welcome $n"))
  } yield ()

main :: Effect Unit
main = log "Hello, World!"

Functional Programming

@volpegabriel87

@gvolpe

  • Haskell
  • PureScript
  • Scala
  • ELM
  • OCaml
  • Nix

 

DevOps industry is choosing Nix for its reproducible builds and immutability

Languages

Functional Programming

@volpegabriel87

@gvolpe

https://nixos.org/releases/nix/nix-1.9/manual/#chap-quick-start

Nixpkgs

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 Advanced issue found
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$ curl https://nixos.org/nix/install | sh
$ nix-env -i hello
$ which hello
/home/user/.nix-profile/bin/hello
$ hello
Hello, world!
$ nix-env -e hello
$ nix-shell -p hello

Functional Programming

@volpegabriel87

@gvolpe

FP languages can be reasoned about mathematically

Functional Programming

@volpegabriel87

@gvolpe

  • Facebook (spam filter in Haskell)
  • Twitter (built on Scala)
  • Google (IT infrastructure in Haskell)
  • Microsoft (serialization system in Haskell)
  • New York Times (image processing in Haskell)

Industry adoption

@volpegabriel87

@gvolpe

https://leanpub.com/pfp-scala 

@volpegabriel87

@gvolpe

pfpscala@gmail.com

<<SCALA MVD>>

https://leanpub.com/pfp-scala 

Gracias totales!

@volpegabriel87

@gvolpe

https://slides.com/volpegabriel/why-fp

why-fp

By Gabriel Volpe

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why-fp

Why Functional Programming?

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