dewey92

interface RemoteData<T> {
  data: T;
  status: 'IDLE' | 'FETCHING' | 'SUCCESS' | 'ERROR'
}

const createRemoteData = <T>(data: T): RemoteData<T> => ({
  data,
  status: 'IDLE',
});

dewey92

-- Data
data Shape
  = Rectangle Number Number -- length, height
  | Triangle Number Number -- base, height
  | Circle Number -- radius
  | Square Number -- length

-- Behaviour
area :: Shape -> Number
area (Rectangle l h) = l * h

dewey92

-- Boolean teridiri dari dua buah value: True dan False
data Bool = True | False

-- List (atau Array) bisa diekspresikan dengan 2 buah data: Nil dan Cons.
-- @example
-- ["Jihad", "Waspada"] == Cons "Jihad" (Cons "Waspada" Nil)
data List a = Nil | Cons a (List a)

-- Beberapa Functor..
data Maybe = Just a | Nothing

dewey92

-- | Instance Array
-- | String is in fact an Array of Char
instance Semigroup [a] where
  (<>) = (++)
instance Monoid [a] where
  mempty = []
  
-- | Instance Num under addition
newtype Sum n = Sum n
instance Num n => Semigroup (Sum n) where

dewey92

const func = createMonoid({
  indentity: x => x,

  // The code below can't run but conceptually valid
  // In Haskell or Purescript, it's easier to write Monoid instance
  semigroup: (f, g) => x => f(x).append(f(g)),
});

// toStr :: Int -> String
const toStr = x => parseInt(x)

dewey92

import React from 'react';

const fragment = children => React.createElement.apply(
  null,
  [React.Fragment, {}].concat(children)
);

const jsx = createMonoid({
  indentity: null,
  semigroup: (a, b) => fragment([a, b]),

dewey92

const endoFunc = createMonoid({
  indentity: x => x,
  semigroup: compose,
});

const incr = x => x + 1;
const square = x => x * x;

log(endoFunc.id) // x => x
log(endoFunc.append(square, incr)(9)) // => 100

dewey92

const cssColor = createMonoid({
  indentity: 'transparent',
  semigroup(a, b) {
    if (a === this.identity) return b;
    if (b === this.identity) return a;
    
    // entah gimana implementasinya
    // ...

    return result;

dewey92

const obj = createMonoid({
  indentity: {},
  semigroup: (a, b) => { ...a, ...b }, // Object.assign({}, a, b)
});

log(obj.id) // => {}
log(obj.append({ a: 1 }, { b: 2 })) // => { a: 1, b: 2 }
log(obj.append({ a: 1 }, obj.id)) // => { a: 1 }

dewey92

// OR
const boolOr = createMonoid({
  indentity: false,
  semigroup: (a, b) => a || b,
});

log(boolOr.id) // => false
log(boolOr.append(true, boolOr.id)) // => true
log(boolOr.append(false, boolOr.id)) // => false