Lens with Const and Identity Functors

const Const = require("./Const")
const Identity = require("./Identity")

const pipe = (...arr) => arr.reduce(
    (acc, next) => x => next(acc(x))
  , x => x
)

const compose = (...arr) => pipe(...arr.reverse());



const lens = (getter, setter) => toFunctorFn =>
    target => {
        
        const functor = toFunctorFn(getter(target))
        
        return functor.map(focus => setter(focus, target))
    };


const view = (lens, x) => lens(Const.pure)(x).run()
  

const over = (lens, f) => x => lens(y => Identity.pure(f(y)))(x).run()

const set = (lens, v) => over(lens, () => v)

const prop = name => lens(x => x[name], (a, x) => ({...x, [name]: a}))

const xLens = lens(x => x.x, (a, s) => {
    return {...s, x: a}
});

const yLens = prop('y')

console.log(
    'view', view(xLens, {x: 12, y: 32})

)

console.log(
    'over', over(xLens, x => x * 2)({x: 12, y: 32})    
)

console.log(
    'set', set(xLens, 42)({x: 12, y: 32})    
)


console.log(
    'set', set(yLens, 42)({x: 12, y: 32})    
)

console.log(
    'set', set(compose(prop('x'), prop('y')), 42)({x: {y: 71, z: 61}, w: 81})    
)

console.log(
    pipe(
        set(prop('x'), 87)
      , over(prop('y'), y => y + 3)
      , over(prop('x'), x => x / 3)
    )({x: 7, y: 1})    
)

console.log(
    'view', view(compose(prop('x'), prop('y')),{x: {y: 71, z: 61}, w: 81})    
)