basic lift

basic-lift.js

// code incomplete, example only

Just.prototype.ap = function(m) {
  
  return m.map(this.value);
};

Nothing.prototype.ap = () => { return this }

function lift2(f, a1, a2){
  
  return a1.map(f).ap(a2)
}


// Maybe -> Number
const a1 = Maybe(2) // Just { value: 2 }

// T -> U -> T
const f = x => fn => fn(x)

// Number -> Number
const sqr = y => y * y

// Maybe -> T -> T -> Maybe -> T
const liftN = lift2(f, a1) 

 // Maybe -> Number -> Number
const boxSquare = Maybe(sqr)

// Maybe -> Number
const squared = liftN(boxSquare) // Just { value: 4 }