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

Stack→pop(): Stack

Stack→top(): mixed

Stack→isEmpty(): 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

chaining operations

Maybe: chain the

null-checking

Many: chain

flatMap

Promise: chain

 functions to be called

with eventual values

jQuery: chain filter

and modify elements

in the DOM

Fluent: chain

changes to a query

When you see yourself chaining operations...

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

...try to use Monads

...and tell your friends

about them

Thanks

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