maybe-vs-either.js

const Maybe = {
  Just: value => ({
    value,
    map: f => Just(f(value)),
    toString: () => `Just(${value})`
  }),
  Nothing: (value = null) => ({
    value: null,
    map: f => Nothing(null),
    toString: () => `Nothing(${value})`
  })
}
const Either = {
  Right: value => ({
    value,
    map: f => Right(f(value)),
    toString: () => `Right(${value})`
  }),
  Left: value => ({
    value, 
    map: f => Left(value),
    toString: () => `Left(${value})`
  }),
}


const{ Just, Nothing } = Maybe;
const { Left, Right } = Either;

/**
 * 
 */


const maybeTotal = (x) => (x === 'total' ? Just(x) : Nothing());
const eitherTotal = x => x === 'total' ? Right(x) : Left('Input is not valid');