Functional 

Programming

The sexy way to code!

Imperative

Line by line

Input: values

Output: values

Modify memory registers/RAM

Functional

Definitions

Substitutions

  e.g y(x) = x + 1

  then y(y(x)) = (x + 1) + 1

Immutable values

State and Change

Do this, then that..

Line by line code

This was a great improvement on the

machine code that preceded it !

Bugs come from the assumption :

lines above the current one have done things in RAM that are needed 

How Bugs Happen..

Pattern Matching

The 'Declarative' Way

Declare the substitutions that can occur..

let secondElementFunction (a:(b:_)) = b

> [1..]  

1,2,3,4,5,6,7,8,9,10,11,12,13......

Infinite Sequences!

> secondElement ( [1..] ) 

2

Can our function handle infinity?!

Lazy Evaluation

• Just make one code substitution
• Dont have to evaluate everything!

Functional Composition

Life after 'line-by-line'

'First-Class' Functions

or 'Lambdas'

Just means to be able to

pass functions as parameters

Functional Composition

asyncCall()
.then(function(data1){
    // do something...
    return anotherAsyncCall();
})
.then(function(data2){
    // do something...  
    return oneMoreAsyncCall();    
})
.then(function(data3){
   // the third and final async response
})
.fail(function(err) {
   // handle any error resulting from any of the above calls    
})
.done();

The alternative to line by line control flow

Declare how functions feed into each other rather than using: shared memory, parameters and return values

Immutability

No mutants allowed!

• Have to copy/patch to change
• Garbage collection
• What about I/O?! (argh MONADS!)

Pros

Cons

• No "Side effects"
• Threadsafe / parallelisable
• Well defined contracts

No Memory Modifications

Streaming

To Infinity and Beyond!

Substitution vs Iteration

Because we can substitute a list with 

its head and then 'the rest' we can reason

about INFINITE data structures!

Reactive

Sorry!

I wanted to give more examples in PHP

Here are some references..

Sorry!

Most of the ladies in this presentation are transexuals 

PHP References

• http://code.tutsplus.com/tutorials/functional-programming-in-php--net-35043
• http://www.php5dp.com/php-functional-programming-part-ii-oop-immutable-objects/
• http://www.garfieldtech.com/blog/functional-php-tour
• https://www.palantir.net/madison-php-2014
• http://www.sitepoint.com/functional-programming-and-php/
• http://www.garfieldtech.com/presentations/dcmunich2012-fp/#1