marcosh

A monad is a particular construction that emerges in the branch of mathematics called category theory. Despite category theory being one of the most abstract field in mathematics, monads are heavily used in functional programming as a design pattern that allows, for example, to manage side-effects. Why should such a powerful design pattern be used only in functional programming languages? Is it possible to apply it also in an Object Oriented paradigm?

In this talk we will try to answer these questions, exploring in parallel the notion of monad in category theory, in functional programming and in object oriented programming, with the help of various examples taken from all the three different worlds.

marcosh

<?php

final class Country
{
    private string $countryCode;
    
    private function __construct(string $countryCode)
    {
        $this->countryCode = $countryCode;
    }

marcosh

PDO::FETCH_FUNC without validation

10: 	0.001568078994751
	0.00071001052856445
	0.00085306167602539
	0.00087618827819824
	0.00083112716674805

100:	0.0012631416320801
	0.0014598369598389

marcosh

{-# LANGUAGE AllowAmbiguousTypes     #-}
{-# LANGUAGE MultiParamTypeClasses   #-}
{-# LANGUAGE FlexibleInstances       #-}
{-# LANGUAGE ScopedTypeVariables     #-}
{-# LANGUAGE TypeApplications        #-}

module NamedTypeclass where

import Prelude hiding (Monoid, mempty, (<>))

marcosh

<?php

declare(strict_types=1);

/**
 * @template F
 * @template A
 * @extends Functor<F,A>
 */
interface Apply extends Functor

marcosh

<?php

declare(strict_types=1);

namespace Marcosh\PhpValidationDSL;

final class Boolean
{
    /** @var Bool */
    private $isTrue;

marcosh

{-# LANGUAGE LambdaCase             #-}
{-# LANGUAGE FunctionalDependencies #-}
{-# LANGUAGE MultiParamTypeClasses  #-}

module Graph where

import Control.Comonad

-- we need to separate `a` and `b` because `a` is covariant while `b` is contravariant => this is actually a profuctor
data PointedGraph moves b a = PointedGraph

marcosh

module Application where

import Data.Profunctor

newtype Application request response =  Application {unApplication :: request -> IO response}

instance Profunctor Application where
    dimap actOnRequest actOnResponse application = Application $ (fmap actOnResponse) . (unApplication application) . actOnRequest

marcosh

Characterize recursable data structures

Recursion

Recursion is a procedure that allows us to iterate through certain data structure. For example we can iterate through lists

sum : List Nat -> Nat
sum list =

marcosh

module Hanoi

import Data.Vect

data Peg
    = First
    | Second
    | Third

-- TODO : can we do better here?