Monads in PHP

Hi, I'm Chris

Based on the work of

Tom Stuart

Monads are an ordinary

data type...

...you're probably

already using them.

What is a stack?

Operations and rules

Operations

 

Stack→push(mixed $value): Stack

Stackpop(): Stack

Stacktop(): mixed

StackisEmpty(): bool

Rules

 

$stack→push($value)→top() == $value

$stack→push($value)→pop() == $stack

$stack→push($value)→isEmpty() == false

(new Stack)→isEmpty() == true

We can implement these however we like...

ArrayStack

LinkedListStack

We can define

more operations...

Stack Size Method

Stack is a specification

common interface

shared functionality

What is a Collection?

Operations and rules

Operations

 

Collection→each(callable $func)

Rules

 

$collection→each($func)

calls $func zero or more times,
in sequence, with a value each time

We can (again) implement these however we like...

ArrayCollection

RangeCollection

We can (again) define

more operations...

Collection Filter Method

Collection is a

specification

common interface

shared functionality

What are stack and collection?

They are

Abstract Data Types

Let's refactor...

Handling null

Handling null

Handling many

Handling many

Why are we doing this?

Similar things

Maybe and Many

are Monads

They are an

Abstract Data Type

Operations and rules

Operations

 

Monad→then(callable $func)

 

Monad→create(...$params)

Rules

 

$monad→then(callable $func)

calls $func zero or more times, always returns instance of same monad

 

$monad→create(mixed $value)

Doesn't alter the value

Monad is a

specification

common interface

shared functionality

We use then to connect multiple operations...

Maybe: do the next thing

if value is not null

Many: do the next thing

for each value

We can (again) define

more operations...

Monad Within Method

Where are we

already using this?

$(".cart")
  .filter(".checkout")
  .on("click", onCheckoutClick);
DB::table("users")
    →where("name", "=", "John")
    →orWhere(function($query) {
        $query
            →where("votes", ">", 100)
            →where("title", "!=", "Admin");
    });

Monads are good for

repeated operations

Maybe: repeat the

null-checking

Many: repeat the

flatMap

Promise: repeatedly add functions to be called

with eventual values

jQuery: repeatedly filter

and modify elements

in the DOM

Fluent: repeatedly change

a query

When you see yourself repeating operations...

...think how you could be using a Monad-like thing

...try to use Monads

...and tell your friends

about them

Thanks

twitter.com/assertchris

slides.com/assertchris

Monads in PHP

By Christopher Pitt

Monads in PHP

Many developers get lost in the hype of object-oriented design. They miss how expressive and succinct their code could be if they tried functional programming. Take Monads, for instance. Many developers have not even heard the name, much less have the ability to describe what Monads are and how they can be useful in every-day code. In this talk, we will gain a clear, simple understanding of what Monads are and how they can help us refactor our code to be clear and concise.

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