FP

Всем, кто начал вникать в functional programming, смотреть и слушать обязательно:

https://youtu.be/E8I19uA-wGY

Основные принципы объясняются настолько доступно, что даже я всё понял.

О чём речь, собственно:

Core Principles of FP design

– functions, types, composition

Functions as parameters

– functions as interface

– partial application & dependency injection

– continuations, chaining & the pyramid of doom

Monads

– error handling, async

Maps

– dealing with wrapped data

– functors

Monoids

– aggregating data and operations

types are not classes (more like sets, valid input/output values)

types separate data from behaviour, can compose types

algebraic types; product types; sum types (choice/union)

totality, total/partial functions

for composition you need functions with one parameter:

currying – every function is a one parameter function

currying/partial application – dependency injection, continuations

chaining continuations takes us to monads: monadic bind;

use bind to chain error handlers, Railway Oriented Programming

Mappable types are 'functors':

Option.map: lifting operations to Option world / List, Future, … other monads and wrapped types

monoid: math term: closure + 'zero' (identity element) + associativity

semigroup = monoid – zero

any combination of monoids = monoid; define a combinator and get aggregation for free (reduce);

incremental updates, parallelizm, missing data handling

convert non-monoid (customer) to a monoid (customerStats), using map;

… reduce // 'Hadoop make me a sandwich'

convert expensive monoids to cheap monoids: map blocks to aggregated data, incremental updates;

monoid homomorphism

monoid from functions? input type == output type: endomorphism (remember monoid closure?);

all endomorphisms are monoids, you can aggregate them

example: Event Sourcing

monads are monoids: monoid in the category of endofunctors.

Hadoop make me a sandwich:

оригинал ищите в твиттере

Отсмотрено по наводке http://thedeemon.livejournal.com/112356.html

original post http://vasnake.blogspot.com/2016/07/fp.html