SeungUkLee

SeungUkLee

Profiling in Haskell

Do not get bogged down in microoptimizations before you've assessed any macro optimizations that are available. IO and the choice of algorithm dominate any low level changes you may make. In the end you have to think hard about your code!

Before starting to optimize:

1. Is the -O2 flag on ?
2. Profile: which part of the code is the slow one.
3. Use the best algorithm in that part.
4. Optimize: implement it in the most efficient way.

SeungUkLee

In this tutorial we're going to build a set of parser combinators.

What is a parser combinator?

We'll answer the above question in 2 steps

1. what is a parser?
2. and.. what is a parser combinator?

So first question: What is parser?

SeungUkLee

SOLID is FP!

So, I decided to write a little thing, only to practice writing, it's about SOLID being compared between class-based-OO and FP, and there will be grammar errors and there will be a lot of formatting errors, 'bear' with me as I type this as fast as I can. Also correct if I'm wrong. Warning, wall of text in English.

Single responsibility principle

" a class should have only a single responsibility "

A pure function is something with a single responsibility, turning its input into an output. What could be simpler?.

SeungUkLee

// Sorry for poor naming, this example was intented to explain how to use skolem capturing in practise.

interface Stateful<S, A> {
  (state: S): [A, S] 
}

function fmap<S, A, B>(f: (a: A) => B): (stateful: Stateful<S, A>) => Stateful<S, B> {
  return stateful => state => {
    const [a, nextState] = stateful(state);

SeungUkLee

import java.util.Arrays;

public class HashCodeFunctions
{
    private final static short DEFAULT_PRIME_NUMBER = 31;
    
    private HashCodeFunctions()
    {
        throw new AssertionError("Could not be instantiated.");
    }

SeungUkLee

@Override
public boolean equals(Object o) {
  if (this == o) return true;
  if (!(o instanceof Product)) return false;
  Product that = (Product) o;
  //that 이 proxyObject 일 수도 있으므로 getter 로 들고온다.
  return Objects.equals(this.id, that.getId()) &&
         Objects.equals(this.name, that.getName()) &&
         Objects.equals(this.price, that.getPrice());
}

SeungUkLee

    @Override
    public String toString() {
        return new StringBuilder("Product{")
                    .append("id=").append(id)
                    .append(", name='").append(name).append('\'')
                    .append(", price=").append(price)
                    .append('}').toString();
    }

SeungUkLee

GIT을 기반으로 한 프로젝트 개발프로세스

깃을 사용합시다. 깃을 쓰자. 깃을 쓰란 말야!!

• SVN은 변경이력이 많아질수록 속도가 느리지.

  • 커밋 및 처리속도가 빠르다. 변경이력이 많이 축적되어 있어도 속도저하가 거의 없다.

• 커밋찍기가 어렵다.

SeungUkLee

-- likelion
-- haskell 함수를 구현

-- fst
fst' :: (a,b) -> a
fst' (a, _) = a

-- snd
snd' :: (a,b) -> b
snd' (_, b) = b