In search of good design...

transcript

// When I wrote this code, only God and I understood what I was doing// Now, God only knows

Monday, October 8, 12

ABOUT ME

TWITTER.COM/FAUST45GITHUB.COM/FAUST45

Goal of program convert input to reasonable output.

We calculate something and storing temp results in vars, until we can produce complete result.

What is programing about?

Calculates Calculates Calculates

temp results

complete result

temp results

complete result

Program State

temp results

complete result

Program State

Layer control order of calculations

temp results

complete result

Program State

Layer manages access to program state

Looks simple?

temp results

complete result

Program State

Lets add some complexity

Lets make control order layer hard to understand

Let’s split control order layer

and hide in Calculate units

Who can help us?

Lets do the same with state manages layer

Lets makestate manages layer hard to understand

Lets split state manages layer

and hide in Calculate units

Example

Will never happens

Happy debugging suckers

Any part of the program can rewrite state, and it's not easy to

tell where it's happening.

Unit tests don’t save us

Unit test passed success.

Only when you run all program you can touch the bug

Thats most popular programing style, for

today.Imperative

Where the answer?

Functional Programming

Functional model

temp results

complete result

Program State

You construct program from units of pure

calculations

Units of pure calculations have no direct access to

program state

You pass a pice of state in params

function send_money(sender_account, receiver_account, amount_to_send)

and return result of calculations, some new pice of state

function send_money(sender_account, ...) return how_sender_account_looks_after_money_was_send

Calculations depends only from params you passed,

nothing hidden

Calculate

Pice of program state

return result

Program state

Functional

Calculate

Pice of program state

return result

Program state

Imperative

direct access

Rich Hickey

Creator of clojure, language with immutable data by default.

Dialect of Lisp on top of Java Virtual Machine

He was inspired by paper “Out of the Tar Pit”

Model where you don’t rewrite values but

produce new values

Clojure introduce fast immutable data

structures

Implemented with Binary trees

and structure sharing

Mutable data

Resources

★ “Out of the Tar Pit”★ “The Art of Unix Programming”★ “Functional programming is a ghetto” (blog bost by Michael O.Church)★ Rich Hickey videos★ Stuart Holloway videos - “Simplicity Ain't Easy”

In search of good design...

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