Seoh Char seoh

Applied Functional Programming with Scala - Notes

1. Mastering Functions

A function is a mapping from one set, called a domain, to another set, called the codomain. A function associates every element in the domain with exactly one element in the codomain. In Scala, both domain and codomain are types.

val square : Int => Int = x => x * x

This document has moved!

It's now here, in The Programmer's Compendium. The content is the same as before, but being part of the compendium means that it's actively maintained.

Functor and monad examples in plain Java

원문: http://www.nurkiewicz.com/2016/06/functor-and-monad-examples-in-plain-java.html
작성자: Tomasz Nurkiewicz

이 글은 우리가 쓴 책, 'Reactive Programming with RxJava' 의 부록이었다. Reactive programming과 관련이 깊은 주제긴 하지만 모나드를 소개한다는 게 책과 썩 어울리지는 않았다. 그래서 나는 따로 블로그에 올리기로 했다. 프로그래밍을 다루는 블로그에서 *"반은 맞고 반은 틀릴 지 모르는 나만의 모나드 설명"*이란 것이 새로운 *"Hello World"*라는 점을 나도 잘 안다. 하지만 이 글은 펑터(functor)와 모나드(monad)를 자바 자료 구조와 라이브러리라는 각도에서 바라보고 있으며, 이는 공유할 정도의 가치는 있을거라 생각했다.

Explaining Miles's Magic

Miles Sabin recently opened a pull request fixing the infamous SI-2712. First off, this is remarkable and, if merged, will make everyone's life enormously easier. This is a bug that a lot of people hit often without even realizing it, and they just assume that either they did something wrong or the compiler is broken in some weird way. It is especially common for users of scalaz or cats.

But that's not what I wanted to write about. What I want to write about is the exact semantics of Miles's fix, because it does impose some very specific assumptions about the way that type constructors work, and understanding those assumptions is the key to getting the most of it his fix.

For starters, here is the sort of thing that SI-2712 affects:

def foo[F[_], A](fa: F[A]): String = fa.toString

Directly from CLI

alias x='exit'
funcsave x

or create a file in

~/.config/fish/functions

with name

System Design Cheatsheet

Picking the right architecture = Picking the right battles + Managing trade-offs

Basic Steps

Clarify and agree on the scope of the system

User cases (description of sequences of events that, taken together, lead to a system doing something useful)
- Who is going to use it?
- How are they going to use it?

These links no longer work. Springer have pulled the free plug.

Graduate texts in mathematics

duplicates = multiple editions

A Classical Introduction to Modern Number Theory, Kenneth Ireland Michael Rosen

	-- http://conscientiousprogrammer.com/blog/2014/08/07/understanding-cloure-transducers-through-types/

	-- Transducer의 자료형을 만들기 위해서는 Rank-2 type이 필요하다.
	{-# LANGUAGE RankNTypes #-}

	-- 함수형 프로그래밍에서 함수는 1급 시민이다. 함수를 조합하고 변환하는 것은 매우 평범한 것이다.
	-- h = (f . g)라면 f (g x) = h x 이다.
	-- reducer는 reduce에서 사용되는 함수에서 다양한 how를 제거하고 일반화하여 정의한 것이다.
	-- 그리고 transducer는 reduce를 새로운 reducer로 변환시키는 함수이다.
	-- haskell의 type system은 새로운 것에 대한 명확한 이해에 도움을 준다.

	// Observable is an Union Type, with the following variants
	const Empty = () => ['EMPTY']
	const Cons = (head, tail) => ['CONS', head, tail]
	const Future = promise => ['FUTURE', promise]

	// race between 2 promises; each promise will resolve to a lazy value
	const lazyRace = (p1, p2) => Promise.race([p1,p2]).then(lazy => lazy())

	// function composition
	const compose = (...fns) => (arg) => fns.reduceRight((res, f) => f(res), arg)

	const daggy = require('daggy');
	const {foldMap} = require('pointfree-fantasy')
	const {concat, toUpper, prop, identity, range, compose} = require('ramda');

	// Contravariant functors usually have this shape F(a -> ConcreteType).
	// In other words, some type holding a function which is parametric on its input, but not output.
	// They don't always have that shape, but it's a good intuition
	// Covariant functors are what we're used to, which are parametric in their output
	//================================================================