[Functional Programming] Draw Items from One JavaScript Array to Another using a Pair ADT

We want to be able to pick nine random cards from an array of twelve cards, but can run into problems of keeping both the cards already draw and the cards left to draw from. Tracking two bits of state like this can create some hard to maintain argument gymnastics when creating our functions. Luckily we have a datatype Pair at our disposal that allows us to combine two values in to one value.

We will use this Pair type to model both a draw pile and a remaining pile, and take advantage of a couple special properties of Pair that will allow us to combine two Pair instances in a meaningful way by chaining. Just like we have done time and time again with the State ADT.

 

We have generated array of cards:

[ 
  { id: 'orange-square', color: 'orange', shape: 'square' },
  { id: 'orange-triangle', color: 'orange', shape: 'triangle' },
  { id: 'orange-circle', color: 'orange', shape: 'circle' },
  { id: 'green-square', color: 'green', shape: 'square' },
  { id: 'green-triangle', color: 'green', shape: 'triangle' },
  { id: 'green-circle', color: 'green', shape: 'circle' },
  { id: 'blue-square', color: 'blue', shape: 'square' },
  { id: 'blue-triangle', color: 'blue', shape: 'triangle' },
  { id: 'blue-circle', color: 'blue', shape: 'circle' },
  { id: 'yellow-square', color: 'yellow', shape: 'square' },
  { id: 'yellow-triangle', color: 'yellow', shape: 'triangle' },
  { id: 'yellow-circle', color: 'yellow', shape: 'circle' } ]

 

By the following code:

const {prop,assoc, pick, State, identity, omit, curry, filter, fanout, converge,map, composeK, liftA2, equals, constant,option, chain, mapProps, find, propEq, isNumber, compose, safe} = require('crocks');
const  {get, modify, of} = State; 

// #region generateCards
const state = {
    colors: [ 'orange', 'green', 'blue', 'yellow' ],
    shapes: [ 'square', 'triangle', 'circle' ]
};

const getState = key => get(prop(key))
const getColors = () => getState('colors').map(option([]))
const getShapes = () => getState('shapes').map(option([]))
const buildCard = curry((color, shape) => ({
    id: `${color}-${shape}`,
    color,
    shape
}));
const buildCards = liftA2(buildCard)
const generateCards = converge(
    liftA2(buildCards),
    getColors,
    getShapes
)
// #endregion

 

Now what we want to do is split cards array into a Pair,

on the left side pair is the selected card array,

on the rigth side pair is the unselected cards array.

// Splite Cards into two pars
//[Selected Cards] - [UnSelected Cards]

const getAt = index => array => array[index];
const unsetAt = index => array => ([...array.slice(0, index), ...array.slice(index + 1)]);
// Deck :: Pair [Card] [Card]
// drawCardAt :: Integer -> [Card] -> Deck
const drawCardAt = index => fanout(
    getAt(index),
    unsetAt(index)
)

console.log(
    generateCards()
        .map(drawCardAt(0))
        .evalWith(state).fst() 
) // { id: 'orange-square', color: 'orange', shape: 'square' }

console.log(
    generateCards()
        .map(drawCardAt(0))
        .evalWith(state).snd()
    
)
/** 
[ { id: 'orange-triangle', color: 'orange', shape: 'triangle' },
  { id: 'orange-circle', color: 'orange', shape: 'circle' },
  { id: 'green-square', color: 'green', shape: 'square' },
  { id: 'green-triangle', color: 'green', shape: 'triangle' },
  { id: 'green-circle', color: 'green', shape: 'circle' },
  { id: 'blue-square', color: 'blue', shape: 'square' },
  { id: 'blue-triangle', color: 'blue', shape: 'triangle' },
  { id: 'blue-circle', color: 'blue', shape: 'circle' },
  { id: 'yellow-square', color: 'yellow', shape: 'square' },
  { id: 'yellow-triangle', color: 'yellow', shape: 'triangle' },
  { id: 'yellow-circle', color: 'yellow', shape: 'circle' } ]
*/

Here we use 'fanout' to generate a Pair.

 

Notice that the left side pair is an object, not an array, we need to use 'bimap' to lift left side pair into Array. To do that,. we use 'bimap'

const drawCardAt = index => compose(
    bimap(Array.of, identity),
    fanout(
        getAt(index),
        unsetAt(index)
    )
)

console.log(
    generateCards()
        .map(drawCardAt(0))
        .evalWith(state).fst() 
) // [{ id: 'orange-square', color: 'orange', shape: 'square' }]

 

---

const {prop,assoc, pick, bimap, State, identity, omit, curry, filter, fanout, converge,map, composeK, liftA2, equals, constant,option, chain, mapProps, find, propEq, isNumber, compose, safe} = require('crocks');
const  {get, modify, of} = State; 

// #region generateCards
const state = {
    colors: [ 'orange', 'green', 'blue', 'yellow' ],
    shapes: [ 'square', 'triangle', 'circle' ]
};

const getState = key => get(prop(key))
const getColors = () => getState('colors').map(option([]))
const getShapes = () => getState('shapes').map(option([]))
const buildCard = curry((color, shape) => ({
    id: `${color}-${shape}`,
    color,
    shape
}));
const buildCards = liftA2(buildCard)
const generateCards = converge(
    liftA2(buildCards),
    getColors,
    getShapes
)
// #endregion

// Splite Cards into two pars
//[Selected Cards] - [UnSelected Cards]

const getAt = index => array => array[index];
const unsetAt = index => array => ([...array.slice(0, index), ...array.slice(index + 1)]);
// Deck :: Pair [Card] [Card]
// drawCardAt :: Integer -> [Card] -> Deck
const drawCardAt = index => compose(
    bimap(Array.of, identity),
    fanout(
        getAt(index),
        unsetAt(index)
    )
)

console.log(
    generateCards()
        .map(drawCardAt(0))
        .map(chain(drawCardAt(2)))
        .map(chain(drawCardAt(3)))
        .map(chain(drawCardAt(4)))
        .evalWith(state).fst() 
) /**
[ { id: 'orange-square', color: 'orange', shape: 'square' },
  { id: 'green-square', color: 'green', shape: 'square' },
  { id: 'green-circle', color: 'green', shape: 'circle' },
  { id: 'blue-triangle', color: 'blue', shape: 'triangle' } ]
*/

console.log(
    generateCards()
        .map(drawCardAt(0))
        .map(chain(drawCardAt(2)))
        .map(chain(drawCardAt(3)))
        .map(chain(drawCardAt(4)))
        .evalWith(state).snd()
    
)
/** 
[ { id: 'orange-triangle', color: 'orange', shape: 'triangle' },
  { id: 'orange-circle', color: 'orange', shape: 'circle' },
  { id: 'green-triangle', color: 'green', shape: 'triangle' },
  { id: 'blue-square', color: 'blue', shape: 'square' },
  { id: 'blue-circle', color: 'blue', shape: 'circle' },
  { id: 'yellow-square', color: 'yellow', shape: 'square' },
  { id: 'yellow-triangle', color: 'yellow', shape: 'triangle' },
  { id: 'yellow-circle', color: 'yellow', shape: 'circle' } ]
*/